NCHurricane2009's Blog

2015 Atlantic Hurricane Season Birdseye Discussion #102

By: NCHurricane2009, 5:06 AM GMT on September 30, 2015

...WEDNESDAY SEPTEMBER 30 2015 1:07 AM EDT...
Alert! Tropical Storm Joaquin (pronounced "Wah-keen") continues to regenerate southward toward the Bahamas into its thunderstorm core and therefore a hurricane watch has been raised for parts of the Bahamas. Preperations in the central and western Bahamas for strong hurricane conditions should immediately begin in case this trend continues for the next 48 hours. Interests in the mid-Atlantic and northeastern US should continue to carefully monitor Joaquin as this storm has the potential to strike these regions as a large-sized and strong hurricane and or non-tropical remnant gale. Continue to visit www.nhc.noaa.gov for up-to-the-minute latest information on Joaquin.

A shortwave upper trough over the northwestern Atlantic has amplified into an upper vortex while continuing to dive southeastward. This upper vortex will reach the waters northeast of the remnants of Ida in the next 24 hours. Upper divergence on the east side of the upper vortex has the potential to trigger a surface trough to the east of the remnants of Ida and to the southeast of Bermuda in about 48 hours. After that time upper winds will become increasingly favorable for tropical development as the upper vortex dissipates. If tropical cyclone formation occurs in this scenario...it is not clear yet if this system will be a seperate entity from the remnants of Ida...or will be Ida itself. See second special feature section below for additional details on this situation. Interests in Bermuda should monitor this situation as this disturbance has potential to move northwestward toward the island.

As mentioned in previous discussions #100 and #101...a deep-layered cyclonic gale has formed in the northeastern Atlantic in the vicinity of the Azores. Even though sea-surface tempeatures in the Azores are only in the 22 deg C range...instability provided by cold temps of the upper layers of the deep-layered gale could cause the gale to evolve into a subtropical cyclone. Currently there are no signs of this occuring. After 72 hours...the upper trough associated with the 995 mb eastern Canada frontal cyclone will amplify into a major upper vortex that will pull the gale northwestward from the Azores...with potential for rough weather to continue as the gale remains strong with the support of the major upper vortex.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1926Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM JOAQUIN...
Current Prognosis...Joaquin is doing well under northerly shear as its surface center has reformed southward into its highly-organized thunderstorm structure...and as a result the tropical storm is on the verge of becoming a hurricane. As of 0000Z earlier this evening the center was located at 26.5N-71.5W.

Atmospheric Outlook for the Forecast Period...Joaquin in the short-term is most likely to continue westward toward the western Bahamas while pushed by the 1029 mb Atlantic surface ridge and 1026 mb surface ridge building over eastern Canada supported by convergence on the back side of the upper trough associated with the 995 mb eastern Canada frontal cyclone. In the next 24 to 48 hours...Joaquin will be sliding directly below the upper ridge axis expanding into the western Atlantic (marked by blue-zig-zag line to the left of Joaquin in the above atmospheric features chart)...which will provide a low shear/enhanced upper outflow environment that will increase the chances of Joaquin strengthening into a significant hurricane. The upper trough currently over eastern North America (marked by blue-dashed line) will fracture...with Joaquin interacting with the southern fracture of the upper trough by 72 hours and beyond. Northerly winds on the west side of Joaquin is expected to induce southward cool air advection that will cause the southern fracture to amplify into a northwest-southeast tilt...a configuration which will create massive upper air divergence ahead of the southern fracture that will cause Joaquin to transition into a strong non-tropical remnant gale while moving into the mid-Atlantic or northeastern US.

Thermodynamic Outlook for the Forecast Period...Joaquin is currently over 30 deg C waters very favorable for tropical development. However by 72 to 96 hours Joaquin will have crossed the 26 deg C isotherm into cooler waters that will aid in the transition of Joaquin to non-tropical.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Oct 1)...90 mph maximum sustained wind hurricane centered east of the northwestern Bahamas at 26.5N-73W

48 Hr Forecast (0000Z Oct 2)...110 mph maximum sustained wind hurricane centered near the northwestern Bahamas at 27.5N-76W

72 Hr Forecast (0000Z Oct 3)...105 mph maximum sustained wind hurricane centered offshore of the southeastern US at 31N-76W

96 Hr Forecast (0000Z Oct 4)...85 mph maximum sustained wind hurricane centered over the North Carolina/Virginia Border at 37N-76W

120 Hr Forecast (0000Z Oct 5)...60 mph maximum sustained wind non-tropical remnant gale centered over far eastern Pennsylvania at 41.5N-76W

Track Forecast...Many of the dynamical computer models continue to shift the short-term track forecast southward...perhaps due to the fact the models expect Joaquin's surface center to continue to regenerate southward into its well-organized thunderstorm structure in the short-term. Therefore my updated forecast track is essentially a southward adjustment from my previous while showing a slower and more gradual progression to the north. My previous forecast track philosophy was that the cold front of the 995 mb eastern Canada frontal cyclone (wedged between the 1026 mb surface ridge building in eastern Canada and 1029 mb Atlantic surface ridge) would help initialize the turn to the north...but now with Joaquin expected to stay further to the south interaction with this front is no longer expected and therefore my updated forecast track is also a slight west adjustment over my previous while delaying when Joaquin turns north.

Intensity Forecast...Joaquin is once again stronger than my previous intensity forecast...and so I have once again bumped up my updated intensity forecast. By 72 hours and beyond I show weakening due to cooler waters and increasing shear as Joaquin interacts with the southern fracture of an upper trough...but this interaction (detailed in the above atmospheric outlook section) will cause Joaquin to only slowly weaken.

Impact Forecast...In anticipation of additional strengthening...my impact swath shows growth of the current 11 PM EDT NHC tropical storm wind field along my forecast track. I keep the swath lopsided to the east due to interaction with the southern fracture of an upper trough that will keep storm activity suppressed to the west of the center in the later part of the forecast. Even though I show weakening at 72 to 96 hours...I still expand the size of the swath as Joaquin's wind field could grow due to a large area of surface pressure falls associated with widespread upper divergence ahead of the southern fracture of the upper trough. If a large wind field such as this materializes...a significant storm surge event would occur on the coasts of North Carolina to parts of New England. On a final note...a hurricane watch has just been raised for parts of the Bahamas for a scenario that I did not show in my updated forecast...which is a scenario where Joaquin in the short-term continues to regenerate southward into its thunderstorm core while bombing out into a strong hurricane. Therefore residents in the western and central Bahamas should immediately prepare for strong hurricane conditions in case this scenario unfolds.

...SPECIAL FEATURE...REMNANTS OF IDA (INVEST 90-L)...
Current Prognosis...The remnant surface low of former Tropical Storm Ida is located at 25N-57.5W with disorganied showers and thudnerstorms. Currently treating this situation as if the remnant of Ida will continue westward and away under the influence of the 1029 mb Atlantic surface ridge while the thunderstorms remain stationary while becoming supported by upper divergence on the east side of a northwest Atlantic upper vortex (marked by blue L to the north of Invest 90-L in the above atmospheric features chart) to dig south during the next 24 hours.

Atmospheric Outlook for the Forecast Period...Over the next 72 hours expecting the formation of a surface low near 25N-57.5W in an upper divergence maximum to develop at the boundary between the northwest Atlantic upper vortex digging southward and northeast Atlantic upper vortex associated with the deep-layered 1005 mb gale currently over the Azores. After 72 hours the western Atlantic upper vortex is currently forecast to weaken into a northwest-southeast tilted upper trough with its upper divergence maximum shifting northward and hence causing the surface low to drift northward with the maximum. After 96 hours the dissipating upper trough will be weak enough to no longer influence the track of this system...but perhaps still be applying some light westerly shear (which is why I only currently forecast tropical depression status at 120 hours). By 96 to 120 hours...current expectation is that Joaquin will have evolved into a massive circulation in the western Atlantic/eastern US with the 1026 mb surface ridge currently over eastern Canada moving into the north-central Atlantic. Therefore I currently forecast some northwestward motion in the southeasterly flow between Joaquin and the ridge during that time.

Thermodynamic Outlook for the Forecast Period...This system will be over 28 to 30 deg C waters that will be supportive of tropical cyclone formation.

24 Hr Forecast (0000Z Oct 1)...Disorganized thunderstorms to the east of the remnants of Ida along 25N latitude

48 Hr Forecast (0000Z Oct 2)...Surface trough to the east of the remnants of Ida near 25N-57.5W

72 Hr Forecast (0000Z Oct 3)...Surface trough with surface low centered at 25N-57.5W

96 Hr Forecast (0000Z Oct 4)...Surface low centered at 27.5N-57.5W

120 Hr Forecast (0000Z Oct 5)...35 mph maximum sustained wind tropical depression centered at 30N-60W

2015 Atlantic Hurricane Season Birdseye Discussion #101 (2nd Release)

By: NCHurricane2009, 6:52 AM GMT on September 29, 2015

**This is a second release of this blog update which now includes updated atmospheric and thermodynamics charts**

...TUESDAY SEPTEMBER 28 2015 2:51 AM EDT...
Tropical depression Eleven midway between the Bahamas and Bermuda has become Tropical Storm Joaquin (pronounced "Wah-keen"). The long-range outlook on Joaquin has changed and now Joaquin has a high chance to strike the northeastern United States within the next five days...see special feature section below for additional details on this developing situation. Interests in the mid-Atlantic and northeastern United States should pay strong attention to Joaquin...visit www.nhc.noaa.gov for up to the minute latest information on this storm.

Surface trough low Invest 99-L in the eastern Gulf of Mexico...supported by upper divergence on the east side of the western Gulf of Mexico/Texas upper vortex...has not become better organized in part due to wind shear from the upper vortex. This system has run out of time to become a tropical cyclone before it makes landfall in the southeastern US. The remnants of 99-L will bring heavy rain with flash flooding potential across Florida and the southeastern US...especially over grounds that have already been soaked by previous tropical disturbance 97-L that recently moved into the southeastern US.

A shortwave upper trough over the northwestern Atlantic (marked by blue-dashed line north of Joaquin in the atmospheric features chart below) continues to dive southeastward. This shortwave upper trough will become amplified while reaching the waters to the northeast of the remnants of Ida by 24 to 48 hours. Upper divergence on the east side of the shortwave has the potential to trigger a surface trough to the east of the remnants of Ida and to the southeast of Bermuda in about 48 to 72 hours. Depending on how much upper ridging developes to the east of the shortwave...this surface trough could evolve into yet another tropical disturbance during that time. It is not clear yet if such a tropical disturbance will be a seperate entity from the remnants of Ida...or will be Ida itself.

Stormy weather in the north-central Atlantic and over the Azores islands with potential for subtropical cyclone development possible over the next few days. The strong 1030 mb Atlantic surface ridge is teaming up with upper ridging amplifying due to warm air advection ahead of the frontal cyclone currently over central Canada...which will result in a deep-layered ridge that will pass north of the Azores and into Europe. This deep-layered ridge is cuting-off a portion of the surface front and upper trough extending from the frontal cyclone east of Greenland into a deep-layered cyclonic gale in the vicinity of the Azores. Even though sea-surface tempeatures in the Azores are only in the 22 deg C range...instability provided by cold temps of the upper layers of the deep-layered gale could cause the gale to evolve into a subtropical cyclone. After 96 hours...the upper trough associated with the 984 mb central Canada frontal cyclone will amplify into a major upper vortex that will pull the gale northwestward from the Azores...with potential for rough weather to continue as the gale remains strong with the support of the major upper vortex.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1929Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM JOAQUIN...
Current Prognosis...Tropical depression eleven has intensified further into the tenth named storm of the Atlantic Hurricane Season...Tropical Storm Joaquin (pronounced "Wah-keen"). The newly-named tropical storm remains under northerly vertical shear on the east side of an upper ridge expanding into the western Atlantic (marked by blue-zig-zag line to the left of Joaquin in the above atmospheric features chart). This northerly shear is keeping the well-organized thunderstorm bands biased to the south of the center...but visible satellite frames just before sunset and nighttime infrared satellite imagery suggested the swirl center of Joaquin has made a recent southward jump while reforming toward its sheared off storms. As of 0000Z earlier this evening the southward jumping center was located at 27N-70W.

Atmospheric Outlook for the Forecast Period...With the exception of some southward short-term jogging due to the center reforming as noted in the above current prognosis...Joaquin is expected to move northwestward and then northward around the west side of the 1030 mb surface ridge that has recently entered the Atlantic from eastern North America. With the updated forecast track...Joaquin will be directly below the upper ridge expanding into the western Atlantic by 48 hours...which will provide a low shear/enhanced upper outflow environment that will increase the chances of Joaquin strengthening into a hurricane. During this time the upper trough associated with the 984 mb central Canada frontal cyclone will have merged with the upper vortex over the southeastern US associated with disturbance Invest 99-L. But immediately after 48 hours the merged upper trough will split...with the northern fracture passing Joaquin to the north and delivering a strong surface ridge over eastern Canada (supported by upper convergence on the back side of the northern fracture) that will prevent Joaquin from going out to sea. Meanwhile Joaquin itself will interact with the remaining southern fracture of the upper trough...with northerly winds on the west side of Joaquin creating southward cool air advection that will cause the southern fracture to amplify into a northwest-southeast tilt...a configuration which will create massive upper air divergence ahead of the southern fracture that will cause Joaquin to transition into a strong non-tropical remnant gale while moving into the northeastern US.

Thermodynamic Outlook for the Forecast Period...Joaquin is currently over 30 deg C waters very favorable for tropical development. However by 96 hours Joaquin will have crossed the 26 deg C isotherm into cooler waters that will aid in the transition of Joaquin to non-tropical.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 30)...60 mph maximum sustained wind tropical storm centered at 25.7N-72W

48 Hr Forecast (0000Z Oct 1)...75 mph maximum sustained wind hurricane centered at 29N-73W

72 Hr Forecast (0000Z Oct 2)...70 mph maximum sustained wind tropical storm centered just offshore of North Carolina at 33N-73W

96 Hr Forecast (0000Z Oct 3)...70 mph maximum sustained wind tropical storm transitioning to non-tropical centered just offshore of southern New Jersey...centered at 39N-73W

120 Hr Forecast (0000Z Oct 4)...50 mph non-tropical remnant gale crossing the New York/Canada border...centered at 45N-73W

Track Forecast...Due to the current observations of Joaquin reforming to the south...I have adjusted all my early forecast points southward accordingly. The later part of my forecast track is adjusted westward to account for a forecast eastern Canada surface ridge and forecast interaction with a southern fracture of an upper trough (all mentioned in the above atmospheric outlook section) that will now prevent Joaquin from going out to sea.

Intensity Forecast...Joaquin is stronger than my previous intensity forecast. I now forecast some brisk development in the next 24 hours with anticipation that Joaquin continues to reform southward into its highly-organized thunderstorm structure. I then forecast intensification into a hurricane by 48 hours after Joaquin arrives directly below the western Atlantic upper ridge axis which will reduce shear and enhance its upper outflow. Beyond 48 hours I show weakening due to cooler waters and increasing shear as Joaquin interacts with the southern fracture of an upper trough...but this interaction (detailed in the above atmospheric outlook section) will cause Joaquin to only slowly weaken.

Impact Forecast...Impact swath shows growth of the current 11 PM EDT NHC tropical storm wind field along my forecast track. I keep the swath lopsided to the east due to interaction with the southern fracture of an upper trough that will keep storm activity suppressed to the west of the center in the later part of the forecast. Even though I show weakening on Thursday and Friday...I still expand the size of the swath as Joaquin's wind field could grow due to a large area of surface pressure falls associated with widespread upper divergence ahead of the southern fracture of the upper trough.

2015 Atlantic Hurricane Season Birdseye Discussion #101

By: NCHurricane2009, 6:14 AM GMT on September 29, 2015

**Currently dealing with technical difficulties updating the atmospheric and thermodynamic outlook charts from my previous update. I am releasing this blog update now without updated charts due to the changes with Tropical Storm Joaquin which now increases the threat to the northeastern United States**

...TUESDAY SEPTEMBER 29 2015 2:12 AM EDT...
Tropical depression Eleven midway between the Bahamas and Bermuda has become Tropical Storm Joaquin (pronounced "Wah-keen"). The long-range outlook on Joaquin has changed and now Joaquin has a high chance to strike the northeastern United States within the next five days...see special feature section below for additional details on this developing situation. Interests in the mid-Atlantic and northeastern United States should pay strong attention to Joaquin...visit www.nhc.noaa.gov for up to the minute latest information on this storm.

Surface trough low Invest 99-L in the eastern Gulf of Mexico...supported by upper divergence on the east side of the western Gulf of Mexico/Texas upper vortex...has not become better organized in part due to wind shear from the upper vortex. This system has run out of time to become a tropical cyclone before it makes landfall in the southeastern US. The remnants of 99-L will bring heavy rain with flash flooding potential across Florida and the southeastern US...especially over grounds that have already been soaked by previous tropical disturbance 97-L that recently moved into the southeastern US.

A shortwave upper trough over the northwestern Atlantic (marked by blue-dashed line north of Joaquin in the atmospheric features chart below) continues to dive southeastward. This shortwave upper trough will become amplified while reaching the waters to the northeast of the remnants of Ida by 24 to 48 hours. Upper divergence on the east side of the shortwave has the potential to trigger a surface trough to the east of the remnants of Ida and to the southeast of Bermuda in about 48 to 72 hours. Depending on how much upper ridging developes to the east of the shortwave...this surface trough could evolve into yet another tropical disturbance during that time. It is not clear yet if such a tropical disturbance will be a seperate entity from the remnants of Ida...or will be Ida itself.

Stormy weather in the north-central Atlantic and over the Azores islands with potential for subtropical cyclone development possible over the next few days. The strong 1030 mb Atlantic surface ridge is teaming up with upper ridging amplifying due to warm air advection ahead of the frontal cyclone currently over central Canada...which will result in a deep-layered ridge that will pass north of the Azores and into Europe. This deep-layered ridge is cuting-off a portion of the surface front and upper trough extending from the frontal cyclone east of Greenland into a deep-layered cyclonic gale in the vicinity of the Azores. Even though sea-surface tempeatures in the Azores are only in the 22 deg C range...instability provided by cold temps of the upper layers of the deep-layered gale could cause the gale to evolve into a subtropical cyclone. After 96 hours...the upper trough associated with the 984 mb central Canada frontal cyclone will amplify into a major upper vortex that will pull the gale northwestward from the Azores...with potential for rough weather to continue as the gale remains strong with the support of the major upper vortex.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1929Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM JOAQUIN...
Current Prognosis...Tropical depression eleven has intensified further into the tenth named storm of the Atlantic Hurricane Season...Tropical Storm Joaquin (pronounced "Wah-keen"). The newly-named tropical storm remains under northerly vertical shear on the east side of an upper ridge expanding into the western Atlantic (marked by blue-zig-zag line to the left of Joaquin in the above atmospheric features chart). This northerly shear is keeping the well-organized thunderstorm bands biased to the south of the center...but visible satellite frames just before sunset and nighttime infrared satellite imagery suggested the swirl center of Joaquin has made a recent southward jump while reforming toward its sheared off storms. As of 0000Z earlier this evening the southward jumping center was located at 27N-70W.

Atmospheric Outlook for the Forecast Period...With the exception of some southward short-term jogging due to the center reforming as noted in the above current prognosis...Joaquin is expected to move northwestward and then northward around the west side of the 1030 mb surface ridge that has recently entered the Atlantic from eastern North America. With the updated forecast track...Joaquin will be directly below the upper ridge expanding into the western Atlantic by 48 hours...which will provide a low shear/enhanced upper outflow environment that will increase the chances of Joaquin strengthening into a hurricane. During this time the upper trough associated with the 984 mb central Canada frontal cyclone will have merged with the upper vortex over the southeastern US associated with disturbance Invest 99-L. But immediately after 48 hours the merged upper trough will split...with the northern fracture passing Joaquin to the north and delivering a strong surface ridge over eastern Canada (supported by upper convergence on the back side of the northern fracture) that will prevent Joaquin from going out to sea. Meanwhile Joaquin itself will interact with the remaining southern fracture of the upper trough...with northerly winds on the west side of Joaquin creating southward cool air advection that will cause the southern fracture to amplify into a northwest-southeast tilt...a configuration which will create massive upper air divergence ahead of the southern fracture that will cause Joaquin to transition into a strong non-tropical remnant gale while moving into the northeastern US.

Thermodynamic Outlook for the Forecast Period...Joaquin is currently over 30 deg C waters very favorable for tropical development. However by 96 hours Joaquin will have crossed the 26 deg C isotherm into cooler waters that will aid in the transition of Joaquin to non-tropical.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 30)...60 mph maximum sustained wind tropical storm centered at 25.7N-72W

48 Hr Forecast (0000Z Oct 1)...75 mph maximum sustained wind hurricane centered at 29N-73W

72 Hr Forecast (0000Z Oct 2)...70 mph maximum sustained wind tropical storm centered just offshore of North Carolina at 33N-73W

96 Hr Forecast (0000Z Oct 3)...70 mph maximum sustained wind tropical storm transitioning to non-tropical centered just offshore of southern New Jersey...centered at 39N-73W

120 Hr Forecast (0000Z Oct 4)...50 mph non-tropical remnant gale crossing the New York/Canada border...centered at 45N-73W

Track Forecast...Due to the current observations of Joaquin reforming to the south...I have adjusted all my early forecast points southward accordingly. The later part of my forecast track is adjusted westward to account for a forecast eastern Canada surface ridge and forecast interaction with a southern fracture of an upper trough (all mentioned in the above atmospheric outlook section) that will now prevent Joaquin from going out to sea.

Intensity Forecast...Joaquin is stronger than my previous intensity forecast. I now forecast some brisk development in the next 24 hours with anticipation that Joaquin continues to reform southward into its highly-organized thunderstorm structure. I then forecast intensification into a hurricane by 48 hours after Joaquin arrives directly below the western Atlantic upper ridge axis which will reduce shear and enhance its upper outflow. Beyond 48 hours I show weakening due to cooler waters and increasing shear as Joaquin interacts with the southern fracture of an upper trough...but this interaction (detailed in the above atmospheric outlook section) will cause Joaquin to only slowly weaken.

Impact Forecast...Impact swath shows growth of the current 11 PM EDT NHC tropical storm wind field along my forecast track. I keep the swath lopsided to the east due to interaction with the southern fracture of an upper trough that will keep storm activity suppressed to the west of the center in the later part of the forecast. Even though I show weakening on Thursday and Friday...I still expand the size of the swath as Joaquin's wind field could grow due to a large area of surface pressure falls associated with widespread upper divergence ahead of the southern fracture of the upper trough.

2015 Atlantic Hurricane Season Birdseye Discussion #100A (Special Update)

By: NCHurricane2009, 4:00 AM GMT on September 28, 2015

...MONDAY SEPTEMBER 28 2015 12:00 AM EDT...
This special update is to update the status of Tropical Depression Ida and tropical disturbance Invest 98-L.

Ida has dissipated into a remnant low while moving westward toward the western Atlantic. This is my final statement on Ida on this blog unless the remnants later show signs of regeneration.

Tropical disturbance Invest 98-L midway between the Bahamas and Bermuda has become tropical depression eleven. As such I have updated my special feature section on Invest 98-L as shown below.

See full discussion #100 for an update on the rest of the Atlantic tropics...including an update on tropical disturbance Invest 99-L moving into the eastern Gulf of Mexico.

...SPECIAL FEATURE...TROPICAL DEPRESSION ELEVEN...
Current Prognosis...Surface low Invest 98-L midway between Bermuda and the Bahamas has strengthened into the eleventh tropical depression of the 2015 Atlantic Hurricane Season. The new tropical depression is under northerly vertical shear on the east side of an upper ridge expanding into the western Atlantic. This northerly shear is keeping the well-organized thunderstorm bands biased to the southeast of the center (located at 27.5N-68.7W as of 0000Z).

Atmospheric Outlook for the Forecast Period...Tropical depression eleven is expected to move northwestward and then northward around the west side of the 1034 mb surface ridge emerging from North America. With the updated forecast track...the tropical depression will be directly below the upper ridge expanding into the western Atlantic by 72 hours...which will provide a low shear/enhanced upper outflow environment that will increase the chances of the depression strengthening into a tropical storm. By 96 hours the cold front of the frontal cyclone currently over western Canada will have moved offshore and absorb this tropical cyclone...causing its transition to a non-tropical frontal depression supported by upper divergence on the east side of the upper trough associated with the front.

Thermodynamic Outlook for the Forecast Period...Eleven is currently over 30 deg C waters very favorable for tropical development. However by 96 hours Eleven will be approaching the 26 deg C isotherm which will aid in the transition of Eleven into non-tropical status.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 29)...35 mph maximum sustained wind tropical depression centered at 27.6N-70W

48 Hr Forecast (0000Z Sep 30)...35 mph maximum sustained wind tropical depression centered at 29N-72W

72 Hr Forecast (0000Z Oct 1)...45 mph maximum sustained wind tropical storm centered at 33N-73W

96 Hr Forecast (0000Z Oct 2)...Remnant non-tropical low centered at 37.5N-70W

Track Forecast...I am showing the same track forecast line as shown in my previous forecasts...but I am showing a much slower progress along that line due to the fact the tropical depression has essentially been stationary and has not started moving yet.

Intensity Forecast...I still show this tropical cyclone reaching tropical storm intensity...but now show this occuring at a later timeframe as the updated forecast track makes it take longer for Eleven to reach the more favorable lower shear/enhanced upper outflow directly beneath the western Atlantic upper ridge axis.

Impact Forecast...With my impact swath in the above graphic I show a brief period of tropical storm force winds developing in accordance with my updated track and intensity forecast.

2015 Atlantic Hurricane Season Birdseye Discussion #100

By: NCHurricane2009, 6:45 PM GMT on September 27, 2015

...SUNDAY SEPTEMBER 27 2015 2:45 PM EDT...
Tropical Depression Ida becomes poorly organized and is now expected to become a remnant low while heading westward toward the western Atlantic. See first special feature section below for an update on Ida.

Surface trough Invest 99-L intensifies into a cloud swirl surface low while moving from the Yucatan Peninsula of southeastern Mexico and into the southern Gulf of Mexico. However the associated thunderstorms are much less organized compared to 24 hours ago and therefore chances for tropical cyclone formation have reduced. However interests in the eastern Gulf of Mexico should continue to monitor 99-L in case it develops into a tropical depression or weak tropical storm in the next 48 hours. See third special feature section below for an update on 99-L. Regardless of tropical cyclone formation...99-L will bring heavy rain with flash flooding potential across Florida and the southeastern US...especially over grounds that have already been soaked by previous tropical disturbance 97-L that moved into the southeastern US over the last couple of days.

Surface trough Invest 98-L south of Bermuda and north of the Dominican Republic has become better organized while intensifying into a surface low. Tropical cyclone formation appears likely...see second special feature section below for additional details on 98-L. It should be noted that 98-L is likely to dodge all land areas while moving between Bermuda and the east coast of North America.

A shortwave upper trough over the coast of the northeastern US has developed on the back side of the longwave upper trough over the north-central Atlantic...associated with the 987 mb frontal cyclone centered over southern Greenland. This shortwave upper trough will become amplified while diving southeastward on the back side of the longwave...and reach the waters to the northeast of Ida by 48 to 72 hours. Upper divergence on the east side of the shortwave has the potential to trigger a surface trough to the east of Ida and to the southeast of Bermuda in about 72 to 96 hours. Depending on how much upper ridging developes to the east of the shortwave...this surface trough could evolve into yet another tropical disturbance during that time.

Stormy weather in the north-central Atlantic and over the Azores islands with potential for subtropical cyclone development possible over the next few days. The strong 1034 mb surface ridge currently emerging from eastern North America will team up with upper ridging amplifying due to warm air advection ahead of the frontal cyclone currently over western Canada...resulting in a deep-layered ridge that will pass north of the Azores and into Europe. This deep-layered ridge will cut-off a portion of the surface front and upper trough extending from the 987 mb southern Greenland cyclone into a deep-layered cyclonic gale to the east of the Azores by 48 hours...which will then move westward into the Azores by 72 to 120 hours while steered by the south side of the deep-layered ridge. Even though sea-surface tempeatures in the Azores are only in the 22 deg C range...instability provided by cold temps of the upper layers of the deep-layered gale could cause the gale to evolve into a subtropical cyclone. By 120 hours...the cold front of the western Canada frontal cyclone will have absorbed tropical disturbance Invest 98-L in the western Atlatnic...with either the remnants of 98-L or another depression to develop along that front to bomb out into an intense frontal cyclone in the north-central Atlantic as its associated supporting upper trough amplifies into a major upper vortex. This intense north-central Atlantic frontal cyclone will pull the gale northwestward from the Azores and absorb it...but the existence of this intense frontal cyclone will prolong rough weather in the north Atlantic and over the Azores after the gale is gone.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z and 0729Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL DEPRESSION IDA...
Current Prognosis...Ida remains a sheared tropical depression with its low-level cloud swirl center displaced westward from its thundertorm activity (source of the shear mentioned in atmospheric outlook below). Recently the thunderstorms have weakened due to dry air (source of dry air mentioned in thermodynamic outlook below). As of 1200Z earlier this morning the center of Ida passed over 24.8N-48.2W and was moving slowly toward the west.

Atmospheric Outlook for the Forecast Period...The eastern Atlantic upper trough that was shearing Ida has continued to weaken...and the only thing left of this upper trough is a small upper vortex to the east (as marked by a blue L to the east of Ida in the above atmospheric features chart). As such Ida is no longer being sheared by the eastern Atlantic upper trough. However...westerly shear remains unexpectedly high as the upper trough of the 987 mb north-central Atlantic frontal cyclone has joined a cut-off upper vortex to the southwest and therefore I now forecast that Ida will dissipate in the next 24 hours. Ida will continue on a west to west-southwest heading as the 1034 mb eastern North America surface ridge moves offshore and steers Ida.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take Ida across favorable 28 to 30 deg C waters. The above thermodynamics chart shows dry air immediately northwest of Ida...leftover from upper-level convergence and resulting sinking motion of the air on the back side of the eastern Atlantic upper trough that was shearing Ida. With the observation of Ida's thunderstorms weakening in the above current prognosis...it appears this dry air is helping to weaken Ida. This is another reason I now forecast Ida to dissipate in the next 24 hours.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (1200Z Sep 28)...Remnant low centered at 24.5N-51W

Track Forecast...Based on the 1200Z center fix in the above current prognosis Ida is northwest of my previous track forecast...and therefore my updated track forecast is only a westward adjustment over my previous. The reason I have not adjusted the forecast track northward is the 1034 mb ridge emerging from eastern North America is strong enough that Ida will be pushed back southward to at least 24.5N latitude.

Intensity Forecast...Ida is below my previous intensity forecast and I now forecast Ida to dissipate in the next 24 hours due to the observations of weakened storm activity...the unexpectedly higher westerly shear noted in the above atmospheric outlook section...and due to the dry air mentioned in the above thermodynamic outlook section.

Impact Forecast...With Ida likely to weaken to a remnant low...no signficant impacts are expected.

...SPECIAL FEATURE...SURFACE LOW INVEST 98-L...
Current Prognosis...Surface low Invest 98-L located south of Bermuda and north of the Dominican Republic in the western Atlantic remains supported by upper divergence at the boundary between two cells of upper vorticity (one marked by a blue-dashed line immediately over 98-L in the above atmospheric features chart...the other marked by a blue L to the southeast of 98-L). This upper vorticity is shifting southeastward...placing 98-L under some northerly vertical shear between the west side of the upper vorticity and east side of the upper ridge expanding into the western Atlantic (marked by blue-zig-zag line to the left of 98-L). This northerly shear is keeping the well-organized thunderstorm bands biased to the southeast of the center (located at 27N-69W as of 1200Z). This northerly shear is not too bad at the moment due to a couple of upper-level features deflecting some of the northerly upper winds...specifically the upper vorticity immediately over 98-L and an upper ridge axis between the two cells of upper vorticity...marked by blue-zig-zag line immediately east of 98-L. However I still prefer to forecast tropical cylcone formation at 48 hours as upper wind forecasts indicate that 98-L will still be under some northerly vertical shear in the next 24 hours.

Atmospheric Outlook for the Forecast Period...98-L is expected to move northwestward and then northward around the west side of the 1034 mb surface ridge emerging from North America. By 48 hours 98-L will be directly below the upper ridge expanding into the western Atlantic...which will provide a low shear/enhanced upper outflow environment that will increase the chances of tropical cyclone formation. By 96 hours 98-L will turn northeastward in the northwestern Atlantic ahead of the upper trough currently over western North America...with 98-L transitioning into a non-tropical remnant low supported by upper divergence on the east side of the upper trough. I have significantly slowed 98-L's forecast northeast speed for this timeframe as the surface ridge to build in the upper convergence on the back side of the upper trough is forecast to be stronger and block the northeast progress of 98-L.

Thermodynamic Outlook for the Forecast Period...98-L is currently over 30 deg C waters very favorable for tropical development. However by 72 hours 98-L will be crossing the 26 deg C isotherm into cooler waters that will aid in the transition of 98-L into non-tropical status.

24 Hr Forecast (1200Z Sep 28)...Surface low centered at 29N-72w

48 Hr Forecast (1200Z Sep 29)...45 mph maximum sustained wind tropical storm centered at 33N-73W

72 Hr Forecast (1200Z Sep 30)...50 mph maximum sustained wind tropical storm centered at 37.5N-70W

96 Hr Forecast (1200Z Oct 1)...Remnant non-tropical low centered at 39N-66W

...SPECIAL FEATURE...SURFACE TROUGH INVEST 99-L...
Current Prognosis...Surface trough Invest 99-L over the Yucatan peninsula of southeastern Mexico...supported by upper divergence on the east side of an upper vortex over the western Gulf of Mexico/Texas...has intensified into a well-defined cloud swirl surface low that has recently moved offshore into the southern Gulf of Mexico. Visible satellite animation suggested that the surface low was centered at 21.5N-87.8W as of 1200Z earlier this morning just prior to moving offshore. This indicates that their is some eastward component of motion relative to yesterday's 1200Z fix...and therefore I have adjusted my forecast track eastward. All associated thunderstorms with this system are biased to the east of the center and are located mostly over the western Caribbean Sea...far eastern Gulf of Mexico...and the Florida peninsula...due to southwesterly vertical shear induced by the aformentioned upper vortex. All associated thunderstorms are less organized relative to 24 hours ago...and therefore I have significantly lowered my intensity forecast on this system.

Atmospheric Outlook for the Forecast Period...Invest 99-L will continue north-northeast across the eastern Gulf of Mexico over the next 48 hours while in a southerly steering current between the east side of the western Gulf/Texas upper vortex and on the west side of the 1034 mb eastern North America surface ridge. 99-L will remain structured as lopsided tropical system...with the east half of the circulation remaining active while taking advantage of lower shear and enhanced outflow beneath an upper ridge over the eastern Gulf and western Atlantic (marked by blue-zig-zag line to the right of 99-L in the above atmospheric features chart) while the west half remains suppressed by the upper vortex. After 48 hours...I currently forecast that 99-L will quickly weaken to a remnant low moving into the Florida panhandle as the upper vortex in the western Gulf shifts eastward (while opening into an upper trough that merges with the upper trough currenlty over western North America) and seperates all thunderstorms from 99-L.

Thermodynamic Outlook for the Forecast Period...Thermodynamic parameters are favorable for tropical development of 99-L as 99-L moves northward across a moist air mass and 29 to 30 deg C waters covering much of the Gulf of Mexico.

24 Hr Forecast (1200Z Sep 28)...Surface low centered at 24.5N-87W

48 Hr Forecast (1200Z Sep 29)...35 mph maximum sustained wind tropical depression centered in the northeastern Gulf of Mexico at 27.5N-86W

72 Hr Forecast (1200Z Sep 30)...Remnant low centered over the Florida Panhandle at 30.5N-85W

2015 Atlantic Hurricane Season Birdseye Discussion #99

By: NCHurricane2009, 6:33 PM GMT on September 26, 2015

...SATURDAY SEPTEMBER 26 2015 2:33 PM EDT...
Tropical Depression Ida continues to hang on and is expected to turn and accelerate westward toward the western Atlantic ocean over the next five days. See first special feature section below for an update on Ida.

The large area of low surface pressures extending from the remnants of disturbance Invest 97-L over the southeastern US...across the eastern Gulf of Mexico...and into the western Caribbean and Central America has organized into a surface trough over the Yucatan Peninsula over southeastern Mexico supported by the upper divergence maximum of the upper vortex moving into the western Gulf of Mexico from Texas. Due to the organization of the thunderstorms associated with the surface trough...the surface trough has been upgraded to tropical disturbance Invest 99-L. 99-L has a high chance of tropical cyclone formation while moving northward across the Gulf of Mexico over the next 72 hours...see third special feature section below for additional details on this developing situation. Interests in the Gulf of Mexico should continue to monitor 99-L.

Another organizing surface trough has developed in the western Atlantic to the north of the Dominican Republic and south of Bermuda and has been designated as trpoical disturbance Invest 98-L. Upper-level winds could become more conducive for 98-L to organize into a tropical cyclone as 98-L moves northward across the western Atlantic...see second special feature below for additional details on 98-L. It should be noted that 98-L is likely to dodge all land areas while moving between Bermuda and the east coast of North America.

The large upper trough over the north-central Atlantic...associated with the 995 mb frontal cyclone centered just south of Greenland...will deliver a southward diving and amplified shortwave upper trough to the northeast of Ida by 72 and 96 hours. Upper divergence on the east side of the shortwave has the potential to trigger a surface trough to the east of Ida in about 96 to 120 hours. Depending on how much upper ridging developes to the east of the shortwave...yet another tropical disturbance could emerge during that time.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z and 0724Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL DEPRESSION IDA...
Current Prognosis...Ida remains a sheared tropical depression with its low-level cloud swirl center displaced westward from its heavy thundertorm activity (source of the shear mentioned in atmospheric outlook below). As of 1200Z earlier this morning the center of Ida passed over 24N-46W and was moving slowly toward the west to west-northwest.

Atmospheric Outlook for the Forecast Period...Ida continues to be sheared by an upper trough in the eastern Atlantic (this upper trough is marked by a blue-dashed line just northeast of Ida in the above atmospheric features chart). However conditions for Ida have the potential to improve as the upper trough is forecast to weaken. Any re-strengthening of Ida in the improved environment will be gradual as Ida will still be under some light westerly shear due to a belt of weak upper westerlies between the upper trough of the 995 mb north-central Atlantic frontal cyclone and tropical upper ridging to the south. A burst of northwesterly shear will be possible at 72 hours as the upper trough associated with the 995 mb north-central Atlantic frontal cyclone dumps a southward-diving shortwave. By 96 and 120 hours Ida could be rewarded by a favorable low shear and enhanced upper outflow environment while moving below a western Atlantic upper ridge to build in the wake of the 995 mb north-central Atlantic frontal cyclone. Through the forecast period Ida will turn and accelerate westward as the strong 1035 mb North America surface ridge moves into the ocean. By 120 hours Ida will likely bend northward in track while moving toward a ridge weakness created by western Atlantic tropical disturbance Invest 98-L interacting with the upper trough currently over western North America.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take Ida across favorable 28 to 30 deg C waters. The above thermodynamics chart shows dry air immediately northwest of Ida due to upper-level convergence and resulting sinking motion of the air on the back side of the eastern Atlantic upper trough shearing Ida. As the upper trough weakens...it remains to be seen if the residual amounts of this dry air ultimatley kills Ida...or do the warm waters supply enough instability for Ida to fire thunderstorms and moisten out the dry air as atmospheric conditions improve in the wake of the weakening eastern Atlantic upper trough. As shown by my intensity forecast below...I continue to go with the latter scenario.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (1200Z Sep 27)...35 mph maximum sustained wind tropical depression centered at 24.5N-48W

48 Hr Forecast (1200Z Sep 28)...40 mph maximum sustained wind tropical storm centered at 24.5N-50.5W

72 Hr Forecast (1200Z Sep 29)...45 mph maximum sustained wind tropical storm centered at 24.5N-54.5W

96 Hr Forecast (1200Z Sep 30)...50 mph maximum sustained wind tropical storm centered at 24.5N-58.5W

120 Hr Forecast (1200Z Oct 1)...60 mph maximum sustained wind tropical storm centered at 25.5N-61.5W

Track Forecast...Based on the 1200Z center fix in the above current prognosis Ida is east of my previous track forecast...and therefore my updated track forecast is an eastward adjustment over my previous (with my 1200Z forecast points basically being at my 0000Z forecast points shown in my previous forecast).

Intensity Forecast...Ida is below my previous intensity forecast...and so I have lowered my intensity forecast. Intensity forecast philosphy is to show re-strengthening at a gradual rate in lighter westerly shear from 24 to 72 hours...followed by a faster strengthening rate at 96 and 120 hours with Ida expected to move below a favorable low shear/enhanced upper outflow environment beneath a western Atlantic upper ridge as mentioned in the above atmospheric outlook section.

Impact Forecast...Impact swath shows the re-development of a tropical storm wind field with the assumption that Ida re-develops into a tropical storm.

...SPECIAL FEATURE...SURFACE TROUGH INVEST 98-L...
Current Prognosis...A surface trough has developed in the western Atlantic over the last 24 hours to the south of Bermuda and north of the Dominican Republic due to a large upper vortex in the eastern Caribbean and western Atlantic splitting into two upper vortices (marked by pair of blue Ls in the above atmopsheric features chart to the northwest and southeast of 98-L)...with upper divergence at the boundary between the two upper vortices supporting the formation of the surface trough. Visible satellite imagery just after 1200Z suggested that the surface trough was developing a surface spin at 26.5N-68.5W.

Atmospheric Outlook for the Forecast Period...98-L is expected to move northwestward and then northward around the west side of the 1035 mb surface ridge to emerge from North America. As this occurs...the parent upper vorticity is expected to shift southeastward as the western Atlantic upper ridge (marked by blue-zig-zag line to the left of 98-L in the above atmopsheric features chart) expands. This will initially place 98-L under unfavorable northerly vertical shear on the back side of the departing upper vorticity and ahead of the expanding upper ridge...but then by 72 hours 98-L will be directly below the upper ridge which will provide a low shear/enhanced upper outflow environment which will increase the chances of tropical cyclone formation. By 120 hours 98-L will be accelerating rapidly northeastward in the northwestern Atlantic ahead of the upper trough currently over western North America...with 98-L transitioning into a non-tropical remnant low supported by upper divergence on the east side of the upper trough.

Thermodynamic Outlook for the Forecast Period...98-L is currently over 30 deg C waters very favorable for tropical development. However by 96 hours 98-L will be crossing the 26 deg C isotherm into cooler waters that will aid in the transition of 98-L into non-tropical status.

24 Hr Forecast (1200Z Sep 27)...Surface low under northerly vertical shear centered at 27.5N-69W

48 Hr Forecast (1200Z Sep 28)...Well-organized surface low centered at 29N-72w

72 Hr Forecast (1200Z Sep 29)...45 mph maximum sustained wind tropical storm centered at 33N-73W

96 Hr Forecast (1200Z Sep 30)...50 mph maximum sustained wind tropical storm centered at 37.5N-70W

120 Hr Forecast (1200Z Oct 1)...Remnant non-tropical low centered at 41N-58W

...SPECIAL FEATURE...SURFACE TROUGH INVEST 99-L...
Current Prognosis...A surface trough over the Yucatan peninsula of southeastern Mexico is being supported by upper divergence on the east side of an upper vortex moving into the western Gulf of Mexico from Texas. Visible satellite animation suggested that the surface trough is developing a surface rotation that was over the Belize/Mexico border at 18.5N-88.5W as of 1200Z earlier this morning. The well-organized thunderstorms associated with this system are biased to the east of the surface rotation and are located mostly over the western Caribbean Sea due to southwesterly vertical shear induced by the aformentioned upper vortex.

Atmospheric Outlook for the Forecast Period...Surface trough Invest 99-L has a high chance of tropical cyclone formation as it moves northward across the Gulf of Mexico over the next 72 hours while in a southerly steering current between the east side of the upper vortex moving into the western Gulf of Mexico and on the west side of the 1035 mb eastern North America surface ridge. 99-L will remain structured as lopsided tropical system...with the east half of the circulation remaining active while taking advantage of lower shear and enhanced outflow beneath an upper ridge over the eastern Gulf and western Atlantic (marked by blue-zig-zag line to the right of 99-L in the above atmospheric features chart) while the west half remains suppressed by the upper vortex moving into the western Gulf. After 72 hours...I currently forecast that 99-L will quickly weaken while approaching the US Gulf coast as the upper vortex in the western Gulf shifts eastward (while opening into an upper trough that merges with the upper trough currenlty over western North America) and seperates all thunderstorms from 99-L. By 120 hours I forecast that 99-L will have de-generated into a westward drifting remnant low just inland from the US Gulf coast steered by a strengthening surface ridge supported by upper convergence on the back side on what is now the upper trough over western North America.

Thermodynamic Outlook for the Forecast Period...Thermodynamic parameters are favorable for tropical development of 99-L as 99-L moves northward across a moist air mass and 29 to 30 deg C waters covering much of the Gulf of Mexico.

24 Hr Forecast (1200Z Sep 27)...Surface low centered on the North coast of the Yucatan peninsula...at 21.5N-88.5W

48 Hr Forecast (1200Z Sep 28)...45 mph maximum sustained wind tropical storm centered at 24.5N-88.5W

72 Hr Forecast (1200Z Sep 29)...60 mph maximum sustained wind tropical storm centered at 27.5N-88.5W

96 Hr Forecast (1200Z Sep 30)...35 mph maximum sustained wind tropical depression centered over southwestern Alabama at 30.5N-88.5W

120 Hr Forecast (1200Z Oct 1)...Remnant low centered over the Louisiana/Mississippi border at 30.5N-89.8W

2015 Atlantic Hurricane Season Birdseye Discussion #98

By: NCHurricane2009, 6:47 AM GMT on September 25, 2015

...FRIDAY SEPTEMBER 25 2015 2:50 AM EDT...
Tropical Storm Ida expected to move erratically in the central tropical Atlantic over the next few days. See special feature section below for an update on Ida.

An unusually large area of low surface pressures extends from the remnants of disturbance Invest 97-L offshore of the southeastern US...across the eastern Gulf of Mexico...and into the western Caribbean and Central America. This large area of low surface pressure is being induced by widespread upper divergence on the east side of the southeastern US cut-off upper vortex which extends into the Gulf of Mexico. The most active area in this surface low pressure field is over Central America and the western Caribbean...featuring a surface trough just east of Nicaragua (this surface trough continues to be mentioned in the National Hurricane Center tropical weather outlook). Over the next four days...the southeastern US cut-off upper vortex will become replaced by the shortwave upper trough currently over the central US...which will amplify into an upper vortex while sliding eastward into the western Gulf of Mexico due to warm air advection and resulting amplification of an upper ridge to its northwest in advance of a frontal cyclone moving into western Canada. Therefore this large surface low pressure field is expected to organize into a tropical disturbance toward the upper divergence maximum on the east side of the forecast upper vortex...in the central Gulf of Mexico...in about four days. Some significant development of this tropical disturbance is possible in favorable equally amplified upper ridging to develop to the east of the upper vortex and interests in the Gulf of Mexico should monitor this situation carefully over the next few days.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1930Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL DEPRESSION IDA...
Current Prognosis...Ida has weakened to a tropical depression due to vertical wind shear...and remains structured as a sheared cyclone with its low-level cloud swirl center displaced westward from its heavy thundertorm activity (source of the shear mentioned in atmospheric outlook below). As of 0000Z earlier this evening the center of Ida passed over 21.2N-45.2W and was nearly stationary with a slight west or northwest drift.

Atmospheric Outlook for the Forecast Period...Ida continues to be sheared by an upper trough in the eastern Atlantic (this upper trough is marked by a blue-dashed line just north of Ida in the above atmospheric features chart). However conditions for Ida have the potential to improve as the upper trough is forecast to weaken. Ida is drifting northwestward toward the current break between the 1022 mb eastern Atlantic surface ridge and 1037 mb North America surface ridge...but by 96 and 120 hours should accelerate westward as the strong North America surface ridge will have moved offshore.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take Ida across favorable 28 to 30 deg C waters. The above thermodynamics chart shows dry air has increased immediately northwest of Ida due to upper-level convergence and resulting sinking motion of the air on the back side of the upper trough shearing Ida. As the upper trough weakens...it remains to be seen if the residual amounts of this dry air ultimatley kills Ida...or do the warm waters supply enough instability for Ida to fire thunderstorms and moisten out the dry air as atmospheric conditions improve in the wake of the weakening upper trough.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 26)...40 mph maximum sustained wind tropical storm centered at 22.5N-46.5W

48 Hr Forecast (0000Z Sep 27)...45 mph maximum sustained wind tropical storm centered at 23.5N-47.5w

72 Hr Forecast (0000Z Sep 28)...50 mph maximum sustained wind tropical storm centered at 24.5N-49W

96 Hr Forecast (0000Z Sep 29)...50 mph maximum sustained wind tropical storm centered at 24.5N-54W

120 Hr Forecast (0000Z Sep 30)...60 mph maximum sustained wind tropical storm centered at 24.5N-59W

Track Forecast...With current observations of Ida no longer getting dragged eastward by the shearing upper trough (perhaps because she has weakened to a shallow cyclone no longer tall enough to be influenced by the upper trough)...I have adjusted the early part of my updated forecast track westward and show Ida drifting northwestward for the first 72 hours toward the break in the Atlantic surface ridigng mentioned in the above atmospheric outlook section...but then the later part of my forecast track (96 to 120 hours) is similar to my previous while showing Ida accelerating westward as the strong North America surface ridge moves offshore and steers Ida.

Intensity Forecast...Even though Ida is so far following my previous intensity forecast...the fact that the National Hurricane Center and some computer models now predict Ida to soon dissipate beckens the question of whether Ida will or will not survive the dry air (mentioned in the above thermodynamic outlook section) and vertical shear (mentioned in the atmospheric outlook section) in the short term. For the sake of continuity from my previous intensity forecast...I still show Ida surviving as the eastern Atlantic upper trough inducing both the shear and dry air is still forecast to weaken. My intensity forecast shows slow re-strengthening as Ida will still be under some light westerly shear after the eastern Atlantic upper trough dissipates...as the strong upper trough associated with the current 998 mb frontal cyclone moving into the North Atlantic from Canada will have moved into the ocean...with Ida situated in a belt of weak upper-level westerlies to the south of the upper trough and to the north of tropical upper ridging. However I have slightly lowered my intensity forecast as the latest GFS upper-level wind forecast is slower to dissipate the eastern Atlantic upper trough...and now shows the upper trough associated with the 998 mb frontal cyclone dumping a southward-diving shortwave that could induce a burst of northwesterly shear on Ida at 96 hours. However if Ida survives that...she will be rewarded by a favorable low shear/enhanced upper outflow environment at 120 hours under a western Atlantic upper ridge to build in the wake of the 998 mb frontal cyclone.

Impact Forecast...Impact swath shows the re-development of a tropical storm wind field with the assumption that Ida re-develops into a tropical storm.

2015 Atlantic Hurricane Season Birdseye Discussion #97

By: NCHurricane2009, 5:17 AM GMT on September 24, 2015

...THURSDAY SEPTEMBER 24 2015 1:18 AM EDT...
Tropical Storm Ida expected to move erratically in the central tropical Atlantic over the next few days. See special feature section below for an update on Ida.

An unusually large area of low surface pressures extends from the remnants of disturbance Invest 97-L offshore of the southeastern US...across the eastern Gulf of Mexico...and into the western Caribbean and Central America. This large area of low surface pressure is being induced by widespread upper divergence on the east side of the southeastern US cut-off upper trough which extends into the Gulf of Mexico. The most active area in this surface low pressure field is over Central America and the southern Caribbean...featuring a surface trough just east of Nicaragua showing light rotation (this surface trough has become introduced into the National Hurricane Center tropical weather outlook). Over the next five days...the southeastern US cut-off upper trough will become replaced by the shortwave upper trough currently over the southwestern US...which will amplify into an upper vortex while sliding eastward into the Gulf of Mexico due to warm air advection and resulting amplification of an upper ridge to its northwest in advance of a frontal cyclone moving into western Canada. Therefore this large surface low pressure field is expected to organize into a tropical disturbance toward the upper divergence maximum on the east side of the forecast upper vortex...in the southern Gulf of Mexico...in about five days. Some significant development of this tropical disturbance will be possible in very favorable equally amplified upper ridging to develop to the east of the upper vortex and interests in the Gulf of Mexico should monitor this situation carefully over the next few days.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1918Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM IDA...
Current Prognosis...Tropical Storm Ida remains structured as a sheared cyclone tonight...with its low-level cloud swirl center displaced westward from its heavy thundertorm activity (source of the shear mentioned in atmospheric outlook below). As of 0000Z earlier this evening the center of Ida passed over 19.8N-46W and was drifting eastward.

Atmospheric Outlook for the Forecast Period...Ida continues to be sheared and dragged eastward by an upper trough in the eastern Atlantic (this upper trough is marked by blue-dashed line just north of Ida in the above atmospheric features chart). This upper trough is forecast to decay into a dissipating upper vortex...and as such Ida is expected to move counter-clockwise around the southern periphery of the upper vortex for the first 48 hours. The current break between the 1023 mb eastern Atlantic surface ridge and 1032 mb North America surface ridge is expected to last for the next few days...and so after the upper vortex dissipates Ida is expectd to move northwestward at 72 and 96 hours toward the break in the ridge. Then by 120 hours the North America surface ridge will have moved offshore which will cause Ida to accelerate westward.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take Ida across favorable 28 to 30 deg C waters.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 25)...35 mph maximum sustained wind tropical depression centered at 19.8N-44W

48 Hr Forecast (0000Z Sep 26)...40 mph maximum sustained wind tropical storm centered at 20.3N-42W

72 Hr Forecast (0000Z Sep 27)...45 mph maximum sustained wind tropical storm centered at 22.3N-45w

96 Hr Forecast (0000Z Sep 28)...50 mph maximum sustained wind tropical storm centered at 24.3N-48W

120 Hr Forecast (0000Z Seo 29)...60 mph maximum sustained wind tropical storm centered at 24.3N-53W

Track Forecast...My previous track forecast is doing excellent...with the 0000Z fix in the current prognosis only being 0.3N latitude off. As such my updated track forecast is the same as my previous with a 0.3N latitude adjustment of all points.

Intensity Forecast...Ida has not weakened to a tropical depression as I previously forecasted...and so the early part of my forecast is slightly raised. I still show weakening under the current shear for the first 24 hours...after which time the shear-inducing upper trough will have weakened into a dissipating upper vortex and so I begin to show slow re-strengthening at 48 hours and beyond. For now I am keeping the re-strengthening rate only gradual as Ida will be under some light westerly shear as the strong upper trough associated with the current 986 mb eastern Canada frontal cyclone will have moved into the ocean...with Ida situated in a belt of weak upper-level westerlies to the south of the upper trough and to the north of tropical upper ridging.

Impact Forecast...Impact swath is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track...with dissipation of the swath where I forecast Ida will weaken below storm force.

2015 Atlantic Hurricane Season Birdseye Discussion #96

By: NCHurricane2009, 7:15 AM GMT on September 23, 2015

...WEDNESDAY SEPTEMBER 23 2015 3:15 AM EDT...
Tropical Storm Ida expected to move erraticaly in the central tropical Atlantic over the next few days. See special feature section below for an update on Ida.

Satellite imagery suggests a vigorous and somewhat organized tropical wave is emerging from the west coast of Africa and into the eastern tropical Atlantic. However additional development of this tropical wave is not likely as dry Saharan air has increased behind Ida and in the path of this tropical wave (as seen in the lower-right corner of the thermodynamics chart below)...and as upper wind forecasts suggest an eastern fragment of the unfavorable upper trough currently shearing Ida will amplify as it moves toward Africa.

The surface frontal boundary low offshore of the Carolinas has been upgraded to tropical disturbance Invest 97-L over the last 24 hours...but is no longer showing signs of organization while struggling in the southwesterly shear induced by the cut-off upper trough over the southeastern US (marked by blue-dashed line to the left of 97-L in the atmospheric features chart below). Therefore I have cancelled this system as a special feature on this blog.

Over the next six days...the shortwave upper trough currently over the southwestern US will be sliding eastward toward the Gulf of Mexico. As it does so...warm air advection ahead of a frontal cyclone moving into western Canada will amplify upper ridging to the northwest of the shortwave upper trough...causing the upper trough to amplifying into a cut-off upper vortex over the western Gulf of Mexico. The GFS...Euro...and CMC computer models suggest upper divergence on the east side of the forecast cut-off upper vortex could trigger a southern Gulf of Mexico disturbance in about six days which could undergo tropical development in equally amplified and favorable upper ridging to the east of the cut-off upper vortex. Plenty of time to watch this unfold over the next days...stay tuned...

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1930Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM IDA...
Current Prognosis...Tropical Storm Ida remains structured as a sheared cyclone tonight...with its low-level cloud swirl center displaced northwestward from its heavy thundertorm activity (source of the shear mentioned in atmospheric outlook below). As of 0000Z earlier this evening the center of Ida passed over 21N-47W.

Atmospheric Outlook for the Forecast Period...Over the previous 24 hours a shortwave upper trough in the north-central Atlantic has dived southward toward Ida (this upper trough is marked by blue-dashed line just north of Ida in the above atmospheric features chart). This upper trough has induced a burst of northwesterly shear and has caused Ida to stall...as the upper trough tries to drag Ida eastward while the 1027 mb Atlantic surface ridge simultaneously tries to drag Ida westward. Albeit...Ida has been drifting southeastward perhaps as she transitions to a cyclone supported by the upper divergence maximum on the southeast side of the upper trough. This upper trough is forecast to decay into a dissipating upper vortex...and as such Ida is now expected to move counter-clockwise around the southern periphery of the upper vortex for the first 72 hours. The current break between the 1027 mb eastern Atlantic surface ridge and 1029 mb eastern North America surface ridge is expected to last for the next few days...and so after the upper vortex dissipates Ida is likely to move northwestward at 96 and 120 hours toward the break in the ridge.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take Ida across favorable 29 deg C waters.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 24)...35 mph maximum sustained wind tropical depression centered at 19.5N-46W

48 Hr Forecast (0000Z Sep 25)...30 mph maximum sustained wind tropical depression centered at 19.5N-44W

72 Hr Forecast (0000Z Sep 26)...35 mph maximum sustained wind tropical depression centered at 20N-42W

96 Hr Forecast (0000Z Sep 27)...45 mph maximum sustained wind tropical storm centered at 22N-45w

120 Hr Forecast (0000Z Sep 28)...50 mph maximum sustained wind tropical storm centered at 24N-48W

Track Forecast...My previous forecast philosophy was that Ida would de-generate into a shallow cyclone under the current shear and turn westward under the influence of the Atlantic surface ridge while no longer being tall enough to be dragged by the shear-inducing upper trough. Clearly this is not the case...with Ida's surface low pressure center moving southeastward toward the upper divergence maximum of the upper trough while becoming supported by the divergence maximum like a mid-latitude subtropical or non-tropical system. Thus my updated track forecast is a significant eastward shift from my previous while showing a clockwise loop toward the east for the first 72 hours...afterwards showing a northwest track at 96 and 120 hours (see above atmospheric outlook section for the logic behind selecting this track). The latest 0000Z GFS showed Ida essentially moving more east than south for the first 24 hours...but recent infrared satellite animation suggests the low-level center of Ida is instead moving more south and less east and therefore my updated track forecast is based on having Ida to the southwest of the GFS for the first 48 hours...and then building the rest of the forecast from there.

Intensity Forecast...Ida has been slowly weakening due to the shear over the last 24 hours...and so I show Ida continuing to slowly weaken for the first 48 hours. After that time...the shear-inducing upper trough will have weakened into a dissipating upper vortex and so I begin to show slow re-strengthening at 72 hours and beyond. For now I am keeping the re-strengthening rate only gradual as Ida will be under some light westerly shear as the strong upper trough associated with the current 972 mb eastern Canada frontal cyclone will have moved into the ocean...with Ida situated in a belt of weak upper-level westerlies to the south of the upper trough and to the north of tropical upper ridging.

Impact Forecast...Impact swath is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track...with dissipation of the swath where I forecast Ida will weaken below storm force.

2015 Atlantic Hurricane Season Birdseye Discussion #95

By: NCHurricane2009, 4:45 AM GMT on September 22, 2015

...TUESDAY SEPTEMBER 22 2015 12:45 AM EDT...
Tropical Storm Ida expected to move slowly in the central tropical Atlantic over the next few days. See special feature section below for an update on Ida.

Surface trough Invest 96-L offshore of the southeastern United States has transitioned into a frontal boundary dividing the cooler air mass associated with the 989 mb frontal cyclone that has moved offshore from North America from the warmer marine air ahead of the frontal cyclone. The northern part of the surface trough has transitioned into a 1007 mb frontal depression accelerating northeastward offshore of the northeastern US and will remain non-tropical for the duration of its life. Meanwhile the remaining southern portion of the surface trough has intensified into a 1009 mb surface frontal boundary low supported by split flow upper divergence between a dissipating cut-off upper vortex to the south (left behind by the upper trough of the aforementioned frontal cyclone) and mainstream upper southwesterlies in the wake of the upper trough of the frontal cyclone. This new 1009 mb surface low is already showing signs of some tropical development while developing some organizing thunderstorm activity in the north half of its circulation and interests on the coastal Carolinas and Georgia should monitor the progress of this circulation over the next couple of days. See second special feature section below for additional details on this situation.

Over the next seven days...the shortwave upper trough offshore of California that has steered eastern Pacific tropical depression sixteen-E into northwestern Mexico will be sliding eastward toward the Gulf of Mexico. As it does so...warm air advection ahead of a frontal cyclone moving into western Canada will amplify upper ridging to the northwest of the shortwave upper trough...causing the upper trough to amplifying into a cut-off upper vortex over the western Gulf of Mexico. The GFS...Euro...and CMC computer models suggest upper divergence on the east side of the forecast cut-off upper vortex could trigger a southern Gulf of Mexico disturbance in about seven days which could undergo tropical development in equally amplified and favorable upper ridging to the east of the cut-off upper vortex. Plenty of time to watch this unfold over the next days...stay tuned...

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1917Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM IDA...
Current Prognosis...Tropical Storm Ida remains structured as a sheared cyclone tonight...with its low-level cloud swirl center displaced northwestward from its heavy thundertorm activity (source of the shear mentioned in intensity forecast section below). As of 0000Z earlier this evening the center of Ida passed over 22N-49W.

Atmospheric Outlook for the Forecast Period...Over the next 24 hours...a shortwave upper trough in the north-central Atlantic (marked by blue-dashed line in the top-center of the above atmospheric features chart) will dive southward toward Ida. This upper trough will induce a burst of unfavorable northwesterly shear and cause Ida to stall...as the upper trough tries to drag Ida eastward while the 1030 mb Atlantic surface ridge simultaneously tries to drag Ida westward. My current forecast philosophy assumes Ida will resume a westward motion under the influence of the Atlantic surface ridge between 48 and 72 hours after the northwesterly shear causes Ida to weaken to a shallow cyclone that no longer feels the drag of the upper trough. By the end of the forecast period (120 hours)...I forecast Ida will begun to bend northward in track due to the ridge weakness associated with the surface front/troughing currently stalled offshore of the southeastern US and expected to remain quasi-stationary through the forecast period. Ida will encounter another bout of shear during this time while moving westward into upper southwesterly winds on the east side of the TUTT (Tropical Upper Tropospheric Trough) upper vortex currently located just north of Puerto Rico (marked by blue L to the left of Ida in the above atmospheric features chart).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take Ida across very favorable 29 to 30 deg C waters.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 23)...35 mph maximum sustained wind tropical depression centered at 23N-49.5W

48 Hr Forecast (0000Z Sep 24)...Remnant low centered at 23N-50.5W

72 Hr Forecast (0000Z Sep 25)...Remnant low centered at 23N-53W

96 Hr Forecast (0000Z Sep 26)...35 mph maximum sustained wind tropical storm centered at 23N-55.5W

120 Hr Forecast (0000Z Sep 27)...40 mph maximum sustained wind tropical storm centered at 25N-57.5w

Track Forecast...Last night I adjusted my forecast track northward as Ida was catapulting northward...but tonight it is clear Ida has slowed down her northward progress and is south of my previous track forecast. Therefore I have adjusted my track forecast southward accordingly.

Intensity Forecast...Ida has been under westerly shear...because she is on the northwest side of the eastern tropical Atlantic upper ridge (marked by blue H to the southeast of Ida in the above atmospheric features chart) instead of being directly below the center of the upper ridge. Because Ida has not strengthened as much as I forecasted during discussion #94...and in fact has begun to weaken according to the 11 PM EDT NHC advisory...she is now just below my weaker intensity forecast shown in discussion #93 and so my updated intensity forecast is slightly below the intensity forecast in discussion #93. This means I now forecast Ida to de-generate into a remnant low for a time. I still showing weakening for the timeframe that is now at 24 to 48 hours due to the forecast burst of northwesterly shear mentioned in the above atmospheric outlook section...followed by a re-genesis/re-strengthening trend at 72 and 96 hours after the forecast westward track allows the circulation to slide away from the upper trough inducing the northwesterly shear. Then at 120 hours I slow the strengthening rate as Ida moves into less favorable southwesterly shear on the east side of the TUTT upper vortex mentioned at the end of the above atmospheric outlook section.

Impact Forecast...Impact swath is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track...with dissipation of the swath where I forecast Ida will weaken below storm force.

...SPECIAL FEATURE...FRONTAL BOUNDARY SURFACE LOW...
Current Prognosis...A 1009 mb surface low...centered at 32.5N-72.5W...has devleoped offshore of the Carolinas this evening along a surface trough recently turned frontal boundary. This surface low was spawned by split flow upper divergence between a dissipating cut-off upper vortex to the south (marked by blue-dashed line to the south of the 1009 mb low in the above atmospheric features chart) and mainstream mid-latitude upper southwesterlies. Semi-organized thunderstorms are currently flaring in the north half of the circulation.

Atmospheric Outlook for the Forecast Period...In the upper-layers...an upper ridge over the central US is expected to amplify due to low-level warm air advection ahead of a large frontal cyclone currently moving across Canada. In turn...the amplified upper ridge will cause a shortwave upper trough that has been moving across the southern tier of the US (currently located over the southeastern US as marked by a blue-dashed line in the above atmospheric features chart) to amplify into a cut-off upper vortex over the southeastern US. In turn...relatively higher upper atmospheric pressures east of the cut-off upper vortex will result in some favorable upper ridging over the surface low that will reduce...but not entirely eliminate...the current southwesterly vertical shear. Therefore with some shear expected thru the forecast period...I currently have a conservative intensity forecast. The 1026 mb surface ridge currently over the northeastern US will be re-enforced by another surface ridge that builds behind the Canadian frontal cyclone...with the ridge steering this surface low westward into South Carolina or Georgia. However the westward track is expected to be slow as a southwestern lobe of the surface ridge (supported by convergence on the back side of the forecast southeastern US cut-off upper vortex) will extend into the southeastern US and somewhat block the westward progress. I predict weakening as this system moves ashore as this surface low will be entering unfavorable southwesterly shear on the east side of the forecast southeastern US cut-off upper vortex.

Thermodynamic Outlook for the Forecast Period...Favorable Gulf stream waters with temps as high as 30 deg C will help aid any tropical development of this surface low.

24 Hr Forecast (0000Z Sep 23)...Surface low offshore of the Carolinas...centered at 32.5N-74W

48 Hr Forecast (0000Z Sep 24)...45 mph maximum sustained wind tropical storm centered just offshore of South Carolina...at 32.5N-76W

72 Hr Forecast (0000Z Sep 25)...45 mph maximum sustained wind tropical storm centered just offshore of South Carolina...at 32.5N-78.5W

96 Hr Forecast (0000Z Sep 26)...Remnant low over southern South Carolina...centered at 32.5N-81W

2015 Atlantic Hurricane Season Birdseye Discussion #94

By: NCHurricane2009, 5:45 AM GMT on September 21, 2015

...MONDAY SEPTEMBER 21 2015 1:45 AM EDT...
Tropical Storm Ida expected to move slowly in the central tropical Atlantic over the next few days. See special feature section below for an update on Ida.

Surface trough Invest 96-L offshore of the southeastern United States is encountering unfavorable westerly vertical shear associated with the 999 mb frontal cyclone and its upper trough emerging from North America. The north part of this surface trough will become absorbed by the frontal cyclone and upper trough. A southern part of this surface trough could be left behind which later on could allow for some tropical development offshore of the southeastern US when upper-level winds become more favorable when the frontal cyclone and upper trough move away by 24 to 72 hours.

An open ocean widespread area of showers and thunderstorms is being supported by split flow upper divergence between a TUTT (Tropical Upper Tropospheric Trough) upper vortex (marked by a blue L to the northeast of the Lesser Antilles in the atmospheric features chart below) and eastern tropical Atlantic upper ridge (marked by blue H and blue-zig-zag line in the lower-right of the chart). Tropical Storm Ida will be moving northwestward into this area of showers and thunderstorms and dominate the area...and therefore formation of another seperate tropical cyclone from these showers and thunderstorms is not expected.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1917Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM IDA...
Current Prognosis...Tropical Storm Ida remains structured as a sheared cyclone tonight...with its low-level cloud swirl center displaced westward from its heavy thundertorm activity. However the heavy thunderstorm activity has recently intensified and become impressive while expanding partly over the exposed center. As of 0000Z earlier this evening the center of Ida passed over 19N-46.5W...and 3 hours prior (at 2100Z) the center was at 18.2N-46.1W.

Atmospheric Outlook for the Forecast Period...Additional strengthening of Ida is possible in the early part of the forecast due to the low shear/enhanced upper outflow of the eastern tropical Atlantic upper ridge (marked by blue H in the lower-right of the above atmopsheric features chart). Even though Ida is south of the 1030 mb Atlantic surface ridge...Ida has turned northward due to dropping surface pressures south of the ridge induced by upper divergence on the east sides of a cut-off upper trough that has moved offshore from the southeastern US and a TUTT (Tropical Upper Tropospheric Trough...marked by blue L to the left of Ida in the above chart). Currently a shortwave upper trough southeast of Newfoundland (marked by blue-dashed line) will dive southeastward and reach Ida by 48 to 72 hours. This upper trough will induce a burst of unfavorable northwesterly shear and cause Ida to stall...as the upper trough tries to drag Ida eastward while the Atlantic surface ridge simultaneously tries to drag Ida westward. My current forecast philosophy assumes Ida will resume a westward motion under the influence of the Atlantic surface ridge between 72 and 96 hours after the northwesterly shear causes Ida to weaken to a shallow cyclone that no longer feels the drag of the upper trough.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take Ida across very favorable 29 to 30 deg C waters.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 22)...60 mph maximum sustained wind tropical storm centered at 25N-49W

48 Hr Forecast (0000Z Sep 23)...50 mph maximum sustained wind tropical storm centered at 26N-49.5W

72 Hr Forecast (0000Z Sep 24)...45 mph maximum sustained wind tropical storm centered at 26N-50.5W

96 Hr Forecast (0000Z Sep 25)...60 mph maximum sustained wind troipcal storm centered at 26N-53W

120 Hr Forecast (0000Z Sep 26)...70 mph maximum sustained wind tropical storm centered at 26N-55.5W

Track Forecast...Based on the 0000z center fix in the above current prognosis...Ida is well northeast of my previous forecast track...and therefore the first 24 hours of my updated forecast track is adjusted accordingly and is based on the observed 3-hourly motion in the above current prognosis. After 24 hours...my updated forecast track shows Ida stalling...afterwards moving westward by 96 hours and beyond in accordance with the philosophy in the above atmospheric outlook section.

Intensity Forecast...Ida has been under westerly shear...perhaps because she is on the northwest side of the eastern tropical Atlantic upper ridge instead of directly below the center of the upper ridge. However Ida is producing a very impressive thunderstorm burst tonight and therefore my updated intensity forecast is raised. I still showing weakening for the timeframe that is now at 48 to 72 hours due to the forecast burst of northwesterly shear mentioned in the above atmospheric outlook section...followed by a re-strengthening trend at 96 and 120 hours after the forecast westward track allows the circulation to slide away from the upper trough inducing the northwesterly shear.

Impact Forecast...Impact swath is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track.

2015 Atlantic Hurricane Season Birdseye Discussion #93

By: NCHurricane2009, 5:12 AM GMT on September 20, 2015

...SUNDAY SEPTEMBER 20 2015 1:15 AM EDT...
Tropical depression nine dissipates in the central tropical Atlantic due to vertical wind shear. This is my final statement on nine on this blog.

Tropical Storm Ida expected to move slowly in the central tropical Atlantic over the next few days. See special feature section below for an update on Ida.

Surface trough Invest 96-L offshore of the southeastern United States will soon encounter unfavorable westerly vertical shear associated with the 994 mb frontal cyclone and its upper trough currently over eastern North America. It is also possible that this frontal cyclone and upper trough absorbs the surface trough. Or alternatively a portion of this surface trough could be left behind which later on could allow the devlopment of a tropical cyclone offshore of the southeastern US when upper-level winds become favorable again after the frontal cyclone and upper trough move away by 48 to 96 hours.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1930Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM IDA...
Current Prognosis...Tropical Storm Ida is structured as a sheared cyclone tonight...with its low-level cloud swirl center displaced westward from its heavy thundertorm activity. See intensity forecast section below for the source of the vertical shear. As of 0000Z earlier this evening the center of Ida passed over 15.5N-41.8W.

Atmospheric Outlook for the Forecast Period...Some strengthening of Ida is possible in the early part of the forecast if Ida finds a low shear/enhanced upper outflow spot below the eastern tropical Atlantic upper ridge (marked by blue H in the lower-right of the above atmopsheric features chart). Ida will initially be steered westward by the 1026 mb Atlantic surface ridge...with the track bending increasingly northward as the south side of the ridge becomes eaten away due to dropping surface pressures south of the ridge from the Gulf of Mexico to the western Atlantic. This large region of surface pressure falls will be induced by upper divergence on the east sides of a southeastern US cut-off upper trough and a mid-ocean TUTT (Tropical Upper Tropospheric Trough...marked by blue L to the left of Ida in the above chart). Currently an upper trough over Nova Scotia (marked by blue-dashed line) has seperated from the southeastern US cut-off upper trough...and will dive southeastward and reach Ida by 72 to 96 hours. This upper trough will induce a burst of unfavorable northwesterly shear and cause Ida to stall...as the upper trough tries to drag Ida eastward while the Atlantic surface ridge simultaneously tries to drag Ida westward. My current forecast philosophy assumes Ida will resume a westward motion under the influence of the Atlantic surface ridge by 120 hours after the northwesterly shear causes Ida to weaken to a shallow cyclone that no longer feels the drag of the upper trough.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take Ida across favorable 28 to 29 deg C waters.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 21)...45 mph maximum sustained wind tropical storm centered at 17N-48.2W

48 Hr Forecast (0000Z Sep 22)...50 mph maximum sustained wind tropical storm centered at 20N-49.7W

72 Hr Forecast (0000Z Sep 23)...40 mph maximum sustained wind tropical storm centered at 21N-50.2W

96 Hr Forecast (0000Z Sep 24)...30 mph maximum sustained wind tropical depression centered at 21N-51.2W

120 Hr Forecast (0000Z Sep 25)...35 mph maximum sustained wind troipcal depression centered at 21N-53.7W

Track Forecast...Based on the 0000z center fix in the above current prognosis...Ida is a bit northwest of my previous forecast track...and therefore the first part of my updated forecast track is adjusted accordingly and is based on the currently observed 0.8W longitude progress per 3 hours (or 6.4W longitude progress per 24 hours). The later part of the forecast track is adjusted southwestward from my previous in accordance with the latest GFS computer model run.

Intensity Forecast...Ida is apparently under westerly shear...perhaps because she is on the northwest side of the eastern tropical Atlantic upper ridge instead of directly below the center of the upper ridge. Therefore she is below my previous intensity forecast...and I have lowered my intensity forecast while now showing very slow strengthening under the upper ridge. Then by 72 to 96 hours I show weakening due to the forecast burst of northwesterly shear mentioned in the above atmospheric outlook section. I show some recovery of Ida by 120 hours after the forecast westward track allows the circulation to slide away from the upper trough inducing the northwesterly shear...but it is possible that Ida could dissipate early if she does not strengthen before the arrival of the burst of northwesterly shear expected in 72 to 96 hours.

Impact Forecast...Impact swath is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track...with dissipation of the swath for the part of the forecast track where I think Ida will weaken below storm force.

2015 Atlantic Hurricane Season Birdseye Discussion #92

By: NCHurricane2009, 4:03 AM GMT on September 19, 2015

...SATURDAY SEPTEMBER 19 2015 12:10 AM EDT...
Tropical depression nine turns west-northwest in the central tropical Atlantic while currently surviving hostile westerly vertical shear. However the tropical depression is still expected to soon dissipate into a remnant low. See first special feature section below for additional details.

Eastern Atlantic tropical low Invest 95-L strengthens into Tropical Storm Ida. Atmospheric and thermodynamic conditions are quiet favorable for additional development and Ida could become a hurricane within the next few days. See second special feature section below for additional details on newly-formed Ida.

A large area of showers and thunderstorms persists offshore of the southeastern United States...all in association with a surface trough supported by upper divergence on the east side of a cut-off upper trough over the southeastern US. Because the associated showers and thunderstorms have become better organized around the surface trough...the surface trough has been upgraded to tropical disturbance Invest 96-L tonight. While there is some potential for additional development in the near term due to favorable upper ridging ahead of the cut-off upper trough...the surface trough is currently so large and diffuse that it is unlikely it will consolidate into a tropical cyclone before 48 hours...when less favorable westerly vertical shear associated with the 992 mb frontal cyclone and its upper trough currently over central North America hits this surface trough. It is also possible that this frontal cyclone and upper trough absorbs the surface trough during that time. Or alternatively a portion of this surface trough could be left behind which later on could allow the devlopment of a tropical cyclone offshore of the southeastern US when upper-level winds becoming favorable again after the frontal cyclone and upper trough move away by 72 to 120 hours.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1929Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL DEPRESSION NINE...
Current Prognosis...Tropical depression nine is surving in an unfavorable environment of westerly vertical shear while firing pockets of strong thunderstorms near the surface center (source of shear mentioned in atmospheric outlook section below). As of 0000Z infrared satellite imagery suggested the center of nine was located at 18N-48W while moving west-northwestward at a current rate of 1W longitude per 6 hours (or 4W longitude per 24 hours).

Atmospheric Outlook for the Forecast Period...The 980 mb frontal cyclone previously in the northwest Atlantic has lifted northward and away while currently passing southeast of Greenland...with the track of tropical depression nine bending westward as it comes under the steering influence of the 1022 mb Atlantic surface ridge building in the wake of the frontal cyclone. Nine remains under unfavorable westerly shear on the southeast side of a TUTT (Tropical Upper Troposhperic Trough) marked by a blue L to the northwest of the tropical depression in the above atmospheric features chart. Perhaps the reason Nine is currently surving the shear is due to the fact that the TUTT is currenlty in a weakening phase. However the current west-northwest pace of Nine will eventually cause Nine to move into unfavorable upper convergence directly below the center of the TUTT which should cause its dissipation.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across very favorable 29 to 30 deg C waters. However with Nine forecast to move into an environment of unfavorable upper convergence (as mentioned in the above atmospheric outlook)...these warm waters are not expected to help Nine survive.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 20)...30 mph maximum sustained wind tropical depression centered at 19N-52W

48 Hr Forecast (0000Z Sep 21)...Remnant low centered at 20N-56W

Track Forecast...Track forecast is based on continuing the west-northwest pace observed in the current prognosis with the 1022 mb Atlantic surface ridge remaining in place due north of the depression through the forecast period.

Intensity Forecast...Due to the weakening of the westerly shear noted in the above atmospheric outlook section...I have delayed dissipating this system until 0000Z September 21...when the depression will arrive into an unfavorable environment of upper convergence directly below the TUTT (Tropical Upper Tropospheric Trough).

Impact Forecast...No signficant impacts are expected during the forecast period.

...SPECIAL FEATURE...TROPICAL STORM IDA...
Current Prognosis...The low pressure circulation of eastern Atlantic tropical low Invest 95-L has finally intensified into the tenth tropical depression of the 2015 Atlantic Hurricane Season. Very recently...the depression has strengthened to Tropical Storm Ida. As of 0000Z earlier this evening the center of newly-named Ida passed over 13.5N-37W.

Atmospheric Outlook for the Forecast Period...For the first part of the forecast period...upper-level winds will be very favorable for development due to the low shear and enhanced upper outflow of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag line in the lower-right of the above atmopsheric features chart). Ida will be steered westward by the 1024 to 1022 mb Atlantic surface ridge through the forecast period...with the track bending increasingly northward as the south side of the ridge becomes eaten away due to dropping surface pressures south of the ridge from the Gulf of Mexico to the western Atlantic. This large region of surface pressure falls will be induced by upper divergence on the east sides of a southeastern US cut-off upper trough and a mid-ocean TUTT (Tropical Upper Tropospheric Trough). Currently an upper vortex over Massachusetts (marked by blue L in the above chart) is separating from the southeastern US cut-off upper trough...and will dive southeastward and reach this system by the end of the forecast period. This upper vortex will induce a burst of unfavorable northwesterly shear and cause Ida to stall...as the upper vortex tries to drag Ida eastward while the weakened Atlantic surface ridge simultaneously tries to drag Ida westward.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take Ida across favorable 28 to 29 deg C waters.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 20)...60 mph maximum sustained wind tropical storm centered at 15N-40.5W

48 Hr Forecast (0000Z Sep 21)...75 mph maximum sustained wind tropical stormcentered at 16.5N-44W

72 Hr Forecast (0000Z Sep 22)...95 mph maximum sustained wind hurricane centered at 20N-45W

96 Hr Forecast (0000Z Sep 23)...70 mph maximum sustained wind tropical storm centered at 23.5N-46W

120 Hr Forecast (0000Z Sep 24)...60 mph maximum sustained wind tropical storm centered at 23.5N-46W

Track Forecast...Based on the 0000z center fix in the above current prognosis...Ida is 1 longitude east of my previous forecast track and therefore all my updated points are adjusted accordingly. My new 120 hr forecast point shows Ida stalling due to the conflicting steering currents that are expected...as mentioned at the end of the above atmospheric outlook section.

Intensity Forecast...Ida is on par with my previous intensity forecast and therefore I have made no changes. Forecast philosophy is to show strengthening for the first part of the forecast due to the favorable low shear/enhanced outflow mentioned in the first part of the atmospheric outlook...followed by weakening in the second part of the forecast due to the unfavorable burst of northwesterly shear mentioned toward the end of the atmospheric outlook.

Impact Forecast...Impact swath is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track with some growth in anticipation that Ida strengthens further.

2015 Atlantic Hurricane Season Birdseye Discussion #91

By: NCHurricane2009, 4:18 AM GMT on September 18, 2015

...FRIDAY SEPTEMBER 18 2015 12:18 AM EDT...
Tropical depression nine is drifting northward in the central tropical Atlantic...and is expected to dissipate into a remnant low due to unfavorable westerly vertical shear in the next 24 hours. See first special feature section below for additional details.

Satellite imagery also shows vigorous eastern Atlantic tropical low Invest 95-L remains well-organized. Atmospheric and thermodynamic conditions are quiet favorable for additional development of this tropical wave...and therefore there is potential for 95-L to become a strong tropical cyclone within the next five days. See second special feature section below for additional details on this system.

The vigorous tropical wave behind Invest 95-L that recently emerged from western Africa appears to have accelerated westward while becoming absorbed into the broad...large-sized circulation of 95-L. Therefore not expecting this tropical wave to develop.

A large area of showers and thunderstorms currently spans the Florida Peninsula...the northwestern Bahamas...and the western Atlantic waters offshore of the southeastern US...all in association with a surface trough supported by by upper divergence on the east side of a cut-off upper trough over the southeastern US. Some favorable upper ridging has developed ahead of (south and east of) the cut-off upper trough...with potential for tropical development once the surface trough moves across the Florida peninsula and slides below the favorable upper ridging while entering the waters offshore of the southeastern US by 24 to 48 hours. However this broad surface trough may not have enough time to consolidate into a tropical cyclone before 48 hours...when less favorable westerly vertical shear associated with the 1001 mb frontal cyclone and its upper trough currently over the northwestern US hits this surface trough. It is also possible that this frontal cyclone and upper trough absorbs the surface trough during that time. Or alternatively a portion of this surface trough could be left behind which later on could allow the devlopment of a tropical cyclone offshore of the southeastern US when upper-level winds becoming favorable again after the frontal cyclone and upper trough move away.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1930Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL DEPRESSION NINE...
Current Prognosis...Tropical depression nine remains structured as a sheared tropical cyclone...with the surface center remaining decoupled from its heavy thunderstorms (source of shear mentioned in atmospheric outlook section below). As of 0000Z infrared satellite imagery suggested the center of nine was located at 17N-45W while moving northward at a current rate of 0.5N every 3 hours (or 4N every 24 hours).

Atmospheric Outlook for the Forecast Period...Tropical depression nine is continuing northward due to a large area of surface pressure falls to the south of the 1019 mb Atlantic surface ridge (from the Gulf of Mexico all the way into the western Atlantic)...which has caused the tropical depression to enter unfavorable westerly shear on the south side of a TUTT (Tropical Upper Troposhperic Trough) marked by a blue-dashed line to the northwest of the tropical depression in the above atmospheric features chart. This large region of surface pressure falls is being induced by upper divergence on the east side of a southeastern US cut-off upper trough...and as the aforementioned TUTT has recently become re-energized with an injection of vorticity from the passing 988 mb deep-layered frontal cyclone in the northwest Atlantic (with eastern divergence of the re-energized TUTT also contributing to the pressure falls).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across favorable 28 to 29 deg C waters.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 19)...Remnant low centered at 19.5N-46W

Track Forecast...Track forecast philosophy is to show a bend toward the west later in the forecast period because the 988 mb deep-layered northwest Atlantic frontal cyclone will soon pull out which will cause the Atlantic surface ridge to rebuild a bit and push the track more westward. Even though the initial motion in the current prognosis is straight north at a rate of 4N latitude per 24 hours....my 24 hour forecast point is not a 4N translation from the current position...but instead shows a westward deflection from the current straight north motion as the 988 mb frontal cyclone will be pulling out in the next 24 hours.

Intensity Forecast...Tropical depression nine is following the previous intensity forecast...and therefore there are no changes tonight. Therefore tropical depression nine is expected to dissipate into a remnant in the next 24 hours due to the unfavorable westerly shear.

Impact Forecast...No signficant impacts are expected during the forecast period.

...SPECIAL FEATURE...TROPICAL LOW INVEST 95-L...
Current Prognosis...The low pressure circulation of eastern Atlantic tropical low Invest 95-L remains well defined and well-organized and tropical cyclone formation is possible at any time. However it appears the circulation has grown in size and is now a broad system that will take more time to consolidate and strengthen...which is why I have slightly lowered my intensity forecast. As of 0000Z the broad center appeared to pass near 12N-34.5W which is on par with the previous track forecast...and therefore I have made no changes to the track forecast.

Atmospheric Outlook for the Forecast Period...For the first part of the forecast period...upper-level winds will be very favorable for the development of this tropical wave due to the low shear and enhanced upper outflow of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag line in the lower-right of the above atmopsheric features chart). This system will be steered westward by the 1019 mb Atlantic surface ridge through the forecast period...with the track bending increasingly northward as the south side of the ridge becomes eaten away due to dropping surface pressures south of the ridge from the Gulf of Mexico to the western Atlantic. This large region of surface pressure falls will be induced by upper divergence on the east sides of a southeastern US cut-off upper trough and a mid-ocean TUTT (Tropical Upper Tropospheric Trough). By the end of the forecast period...the north fragment of the southeastern US cut-off upper trough will have moved across the ocean and will hit this system with less favorable westerly vertical shear that should cause weakening.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across favorable 28 to 29 deg C waters.

24 Hr Forecast (0000Z Sep 19)...40 mph maximum sustained wind tropical storm centered at 13.5N-38W

48 Hr Forecast (0000Z Sep 20)...60 mph maximum sustained wind tropical storm centered at 15N-41.5W

72 Hr Forecast (0000Z Sep 21)...75 mph maximum sustained wind hurricane centered at 16.5N-45W

96 Hr Forecast (0000Z Sep 22)...95 mph maximum sustained wind hurricane centered at 20N-46W

120 Hr Forecast (0000Z Sep 23)...70 mph maximum sustained wind tropical storm centered at 23.5N-47W

2015 Atlantic Hurricane Season Birdseye Discussion #90

By: NCHurricane2009, 4:21 AM GMT on September 17, 2015

...THURSDAY SEPTEMBER 17 2015 12:21 AM EDT...
Central Atlantic tropical wave Invest 93-L has finally intensified into tropical depression nine. See first special feature section below for more details on this new tropical depression.

Satellite imagery also shows vigorous eastern Atlantic tropical wave Invest 95-L remains well-organized. Atmospheric and thermodynamic conditions are quiet favorable for additional development of this tropical wave...and therefore there is potential for 95-L to become a strong tropical cyclone within the next five days. See second special feature section below for additional details on this system.

Yet another vigorous tropical wave behind Invest 95-L is emerging from the west coast of Africa into the Atlantic tropics. As is the case with 95-L...atmospheric and thermodynamic conditions are quiet favorable for additional development of this tropical wave and this wave will be upgraded to a special feature on this blog should it become better organized in the next 24 hours. However there is a possiblity that conditions later on become less favorable for this tropical wave should 95-L develop into a strong tropical cylcone...in which case less favorable northerly shear induced by the warm core upper anticyclone over 95-L will hit this tropical wave.

A large area of showers and thunderstorms currently spans the eastern Gulf of Mexico..Florida Peninsula...the northwestern Bahamas...southeastern US...and western Atlantic...all in association with the tail end of a decaying surface front enhanced by upper divergence on the east side of a cut-off upper trough over the southeastern US. Recently the decaying surface front has organized into a surface trough in the eastern Gulf of Mexico. Some favorable upper ridging has developed ahead of (south and east of) the cut-off upper trough...with potential for tropical development once the surface trough moves across the Florida peninsula and slides below the favorable upper ridging while entering the waters offshore of the southeastern US by 48 to 72 hours. Therefore if this surface trough becomes better organized over the next 24 hours...I will be upgrading it to a special feature on this blog. After 72 hours the situation will become more interesting due to interaction with the 1001 mb frontal cyclone and its upper trough currently over the northwestern US. It is possible that this frontal cyclone and upper trough absorbs the surface trough during that time...or alternatively a portion of this surface trough could be left behind which will prolong the amount of time this surface trough could become a stalled tropical cyclone offshore of the southeastern US.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1926Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL DEPRESSION NINE...
Current Prognosis...The low pressure circulation of central Atlantic tropical wave Invest 93-L has intensified into the ninth tropical depression of the Atlantic Hurricane Season. Just after forming into a tropical cyclone...the surface center of nine has become seperated from its heavy thunderstorms while entering westerly vertical shear (source of shear mentioned in atmospheric outlook section below). As of 0000Z satellite imagery suggested the center of nine was located at 16N-45W while moving north-northwestward.

Atmospheric Outlook for the Forecast Period...Tropical depression nine is continuing northward due to a large area of surface pressure falls to the south of the 1019 mb Atlantic surface ridge (from the Gulf of Mexico all the way into the western Atlantic)...which has caused the tropical depression to enter unfavorable westerly shear on the south side of an upper vortex (marked by blue L to the north of the tropical depression in the above atmospheric features chart). This large region of surface pressure falls is being induced by upper divergence on the east side of a southeastern US cut-off upper trough...and as the aforementioned upper vortex is about to get re-energized while phasing with the 988 mb deep-layered frontal cyclone in the northwest Atlantic (with eastern divergence of the re-energized upper vortex also contributing to the pressure falls).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across favorable 28 to 29 deg C waters.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 18)...30 mph maximum sustained wind tropical depression centered at 19N-45.5W

48 Hr Forecast (0000Z Sep 19)...Remnant low centered at 21.5N-47.5W

Track Forecast...Because the 0000Z center fix in the above current prognosis is southwest of my previous forecast track...my updated forecast track is adjusted southwestward. Track forecast philosophy is to show a bend toward the west later in the forecast period because the 988 mb deep-layered northwest Atlantic frontal cyclone will pull out which will cause the Atlantic surface ridge to rebuild a bit and push the track more westward.

Intensity Forecast...Tropical depression nine is below my previous intensity forecast and therefore my updated intensity forecast is slightly lower than my previous. I continue to forecast that tropical depression nine will dissipate into a remnant low by 48 hours due to the unfavorable westerly shear.

Impact Forecast...No signficant impacts are expected during the forecast period.

...SPECIAL FEATURE...TROPICAL WAVE INVEST 95-L...
Current Prognosis...The low pressure circulation of eastern Atlantic tropical wave Invest 95-L remains well defined and well-organized and tropical cyclone formation is possible at any time. As of 0000Z 95-L was centered at 11N-30.5W...which is slightly southwest of my previous forecast track and therefore my forecast track is adjusted accordingly.

Atmospheric Outlook for the Forecast Period...Upper-level winds will be very favorable for the development of this tropical wave due to the low shear and enhanced upper outflow of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag line in the lower-right of the above atmopsheric features chart). This system will be steered westward by the 1019 mb Atlantic surface ridge through the forecast period. However the westward track will be bending increasingly northward as the south side of the ridge becomes eaten away due to dropping surface pressures south of the ridge from the Gulf of Mexico to the western Atlantic. This large region of surface pressure falls will be induced by upper divergence on the east side of a southeastern US cut-off upper trough...and as a cut-off upper vortex (marked by blue L north of tropical depression nine) gets re-energized while phasing with the 988 mb northwest Atlantic deep-layered cyclone (with eastern divergence of the re-energized upper vortex also contributing to the pressure falls).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across favorable 28 to 29 deg C waters.

24 Hr Forecast (0000Z Sep 18)...40 mph maximum sustained wind tropical storm centered at 12N-34.5W

48 Hr Forecast (0000Z Sep 19)...60 mph maximum sustained wind tropical storm centered at 13.5N-38W

72 Hr Forecast (0000Z Sep 20)...80 mph maximum sustained wind hurricane centered at 15N-41.5W

96 Hr Forecast (0000Z Sep 21)...100 mph maximum sustained wind hurricane centered at 16.5N-45W

120 Hr Forecast (0000Z Sep 22)...105 mph maximum sustained wind hurricane centered at 20N-46W

2015 Atlantic Hurricane Season Birdseye Discussion #89

By: NCHurricane2009, 9:04 AM GMT on September 16, 2015

...WEDNESDAY SEPTEMBER 16 2015 5:05 AM EDT...
Satellite imagery shows that vigorous central Atlantic tropical wave Invest 93-L has re-gained thunderstorms and is becoming better organized...and therefore tropical cyclone formation is possible in the next 24 hours. See first special feature section below for more details. Any tropical cyclone that develops from this tropical wave will turn northward and avoid the Caribbean Sea.

Satellite imagery also shows vigorous eastern Atlantic tropical wave Invest 95-L remains well-organized. Atmospheric and thermodynamic conditions are quiet favorable for additional development of this tropical wave...and therefore there is potential for 95-L to become a strong tropical cyclone within the next five days. See second special feature section below for additional details on this system.

Yet another vigorous tropical wave behind Invest 95-L is emerging from the west coast of Africa into the Atlantic tropics this early morning. As is the case with 95-L...atmospheric and thermodynamic conditions are quiet favorable for additional development of this tropical wave and this wave will be upgraded to a special feature on this blog should it become better organized in the next 24 hours. However there is a possiblity that conditions become less favorable for this tropical wave by 96 and 120 hours (4 and 5 days) should 95-L develop into a strong tropical cylcone...in which case less favorable northerly shear induced by the warm core upper anticyclone over 95-L will hit this tropical wave.

A large area of showers and thunderstorms currently spans the Gulf of Mexico..Florida Peninsula...the northwestern Bahamas...and western Atlantic...all in association with the tail end of a decaying surface front enhanced by upper divergence on the east side of a cut-off upper trough over the southeastern US. Some favorable upper ridging has developed ahead of (south and east of) the cut-off upper trough...with potential for tropical development if some of this activity organizes below some of the favorable upper ridging. The most likely location for organzing tropical activity will be offshore of the southeastern US in the next 72 hours...after which time the cut-off upper trough and decaying surface front will merge with what is currently the 996 mb frontal cyclone and its upper trough over the northwestern US. Therefore will watch the activity offshore of the southeastern US over the next 72 hours.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1923Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL WAVE INVEST 93-L...
Current Prognosis...The low pressure circulation of central Atlantic tropical wave Invest 93-L has been slowly regaining thunderstorms while becoming increasingly re-organized...and therefore tropical cyclone formation from this system appears likely. As of 0000Z satellite imagery suggested the center of 93-L was located at 13.8N-43W while turning northward.

Atmospheric Outlook for the Forecast Period...The TUTT (Tropical Upper Tropospheric Trough) that sheared apart Grace a few days ago (marked by pair of blue L and blue-dashed line north of 93-L in the above atmospheric features chart) has weakened and lifted northward...allowing the favorable low shear/enhanced upper outflow envionment of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag line in the lower-right of the above atmopsheric features chart) to expand in its wake. Therefore upper-level winds are going to be quiet favorable for tropical development early in the forecast period. 93-L is turning northward due to a large area of surface pressure falls to the south of the 1022 mb Atlantic surface ridge (from the Gulf of Mexico all the way into the western Atlantic)...which will later cause 93-L to weaken from peak intensity while entering unfavorable westerly shear on the southeast side of the TUTT. This large region of surface pressure falls is being induced by upper divergence on the east side of a southeastern US cut-off upper trough and decaying surface frontal boundary...and as the TUTT is about to get re-energized as the main bulk of the upper trough in the northwest Atlantic phases with the TUTT in the next 24 hours (with eastern divergence of the re-energized TUTT also contributing to the pressure falls). My updated forecast track is initially adjusted eastward to account for the initial position and motion being to the right of my previous track...but is later adjusted southwestward from my previous as the 1009 mb frontal cyclone associated with the northwest Atlantic upper trough is shown in models to pull out faster than shown before which will cause the ridge to rebuild a bit and push the track more westward.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across favorable 28 to 29 deg C waters.

24 Hr Forecast (0000Z Sep 17)...45 mph maximum sustained wind tropical storm centered at 17.5N-43.5W

48 Hr Forecast (0000Z Sep 18)...35 mph maximum sustained wind tropical storm centered at 21N-44W

72 Hr Forecast (0000Z Sep 19)...Remnant low centered at 24N-46W

...SPECIAL FEATURE...TROPICAL WAVE INVEST 95-L...
Current Prognosis...The low pressure circulation of eastern Atlantic tropical wave Invest 95-L has seen a decrease in thunderstorms over the last 24 hours but remains well-defined. I have lowered the intensity forecast due to the decrease in thunderstorms. As of 0000Z 95-L was centered at 10.2N-26.2W...which is slightly northwest of my previous forecast track and therefore my forecast track is adjusted accordingly.

Atmospheric Outlook for the Forecast Period...Upper-level winds will be very favorable for the development of this tropical wave due to the low shear and enhanced upper outflow of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag line in the lower-right of the above atmopsheric features chart). This system will be steered westward by the 1022 mb Atlantic surface ridge through the forecast period. However the westward track will be bending increasingly northward as the south side of the ridge becomes eaten away due to dropping surface pressures south of the ridge from the Gulf of Mexico to the western Atlantic. This large region of surface pressure falls will be induced by upper divergence on the east side of a southeastern US cut-off upper trough and decaying surface frontal boundary...and as a cut-off upper vortex (marked by blue L north of 93-L) gets re-energized when the main bulk of the upper trough over the northwest Atlantic and phases with the upper vortex (with eastern divergence of the re-energized upper vortex also contributing to the pressure falls).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across favorable 28 to 29 deg C waters.

24 Hr Forecast (0000Z Sep 17)...35 mph maximum sustained wind tropical storm centered at 11.5N-30.2W

48 Hr Forecast (0000Z Sep 18)...50 mph maximum sustained wind tropical storm centered at 12.5N-34.2W

72 Hr Forecast (0000Z Sep 19)...70 mph maximum sustained wind tropical storm centered at 14N-37.7W

96 Hr Forecast (0000Z Sep 20)...90 mph maximum sustained wind hurricane centered at 15.5N-41.2W

120 Hr Forecast (0000Z Sep 21)...100 mph maximum sustained wind hurricane centered at 17N-44.7W

2015 Atlantic Hurricane Season Birdseye Discussion #88

By: NCHurricane2009, 5:31 AM GMT on September 15, 2015

...TUESDAY SEPTEMBER 15 2015 1:35 AM EDT...
Satellite imagery shows that vigorous eastern Atlantic tropical wave Invest 93-L has lost thunderstorm activity while moving into the central tropical Atlantic. However still watching for possible tropical cyclone formation from this system...see first special feature section below for more details.

Satellite imagery also shows the vigorous tropical wave that recently emerged from Africa into the eastern tropical Atlantic has quickly organized into a tropical low pressure spin...which was upgraded to Invest 95-L on the Naval Research Laboratory site of the US Navy this past afternoon. Atmospheric and thermodynamic conditions are quiet favorable for additional development of this tropical wave...and therefore there is potential for 95-L to become a strong tropical cyclone within the next five days. See second special feature section below for additional details on this system.

A large area of showers and thunderstorms currently spans the Gulf of Mexico..Florida Peninsula...the northwestern Bahamas...and western Atlantic...all in association with the tail end of the surface cold front of the vigorous surface frontal system and upper trough moving offshore from North America. Currently a shortwave upper trough over the central US is diving southeastward on the back side of the upper trough...which over the next couple of days will be left behind as a cut-off southeastern US upper trough with some favorable upper ridging developing ahead of (south and east of) the cut-off. Therefore activity along the decaying tail end of the surface cold front is likely to linger in this region with the support of upper divergence on the east side of the forecast cut-off upper trough...with potential for some tropical development if some of this activity organizes below some of the favorable upper ridging. Indeed this was the case with Invest 94-L in the western Gulf of Mexico...but recently 94-L shows signs of struggling with westerly shear on the north side of the upper ridging and therefore is cancelled as a special feature on this blog. Outside of 94-L...will continue to watch the remainder of the decaying tail end of the front which extends into the western Atlantic.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1909Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL WAVE INVEST 93-L...
Current Prognosis...After appearing to almost become a tropical cyclone last night...over the last 24 hours the low pressure circulation of eastern Atlantic tropical wave Invest 93-L has lost a significant amount of thunderstorms. While it is not perfectly clear why the thunderstorms have weakened...my current best guess is that 93-L has ingested some of the dry Saharan air lingering to the north seen in the bottom-center of the above thermodynamics chart. As of 0000Z earlier this evening 93-L was centered at 12N-40W...which is 1E longitude of where I previously predicted for this evening. Therefore my updated forecast track is the same as previous with a 1E adjustment of all points.

Atmospheric Outlook for the Forecast Period...The TUTT (Tropical Upper Tropospheric Trough) that sheared apart Grace a few days ago (marked by pair of blue Ls to the northwest of 93-L in the above atmospheric features chart) has weakened and lifted northward...allowing the favorable low shear/enhanced upper outflow envionment of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag line in the lower-right of the above atmopsheric features chart) to expand in its wake. Therefore upper-level winds are going to be quiet favorable for tropical development early in the forecast period. 93-L is expected to track westward under the influence of the surface 1026 mb Atlantic subtropical ridge for the next 24 hours. Afterwards..a large area of surface pressure falls to the south of the surface ridge (from the Gulf of Mexico all the way into the western Atlantic) will turn 93-L northward...causing 93-L to weaken from peak intensity while entering unfavorable westerly shear on the southeast side of the TUTT. This large region of surface pressure falls will be induced by upper divergence on the east side of a southeastern US cut-off upper trough and decaying surface frontal boundary to be left behind by the large frontal system currently departing eastern North America...and as the TUTT gets re-energized when the main bulk of the upper trough over eastern North America moves into the ocean and phases with the TUTT by 48 hours (with eastern divergence of the re-energized TUTT also contributing to the pressure falls).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across very favorable 29 deg C waters. Even though the above current prognosis blames adjacent dry saharan air for the weakening of 93-L's thunderstorms...current assumption is that the instability provided by the warm waters will allow 93-L to re-fire thunderstorms that overcome the dry air.

24 Hr Forecast (0000Z Sep 16)...35 mph maximum sustained wind tropical depression centered at 13.5N-44W

48 Hr Forecast (0000Z Sep 17)...45 mph maximum sustained wind tropical storm centered at 16N-46W

72 Hr Forecast (0000Z Sep 18)...35 mph maximum sustained wind tropical storm centered at 21N-46W

96 Hr Forecast (0000Z Sep 19)...Remnant low centered at 25N-46W

...SPECIAL FEATURE...TROPICAL WAVE INVEST 95-L...
Current Prognosis...The vigorous tropical wave that has recently entered the Atlantic from western Africa has become better organized into a tropical low pressure spin with spiral thunderstorm bands...on schedule with my previous forecast. The tropical low was upgraded to Invest 95-L on the Naval Research Laboratory site of the US Navy this past afternoon. As of 0000Z 95-L was centered at 9N-21.5W...which is southeast of my previous forecast track and therefore my forecast track is adjusted accordingly. Satellite animation from 1800Z to 0000Z showed the center move from 20.5W to 21.5W...which is a rate of progression of 1W per 6 hours (or 4W per 24 hours). My updated forecast track is initialized based on this rate of progression.

Atmospheric Outlook for the Forecast Period...Upper-level winds will be very favorable for the development of this tropical wave due to the low shear and enhanced upper outflow of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag line in the lower-right of the above atmopsheric features chart). This system will be steered westward by the 1026 mb Atlantic surface ridge through the forecast period. However the westward track will be bending increasingly northward as the south side of the ridge becomes eaten away due to dropping surface pressures south of the ridge from the Gulf of Mexico to the western Atlantic. This large region of surface pressure falls will be induced by upper divergence on the east side of a southeastern US cut-off upper trough and decaying surface frontal boundary to be left behind by the large frontal system currently departing eastern North America...and as a cut-off upper vortex (marked by pair of blue Ls northwest of 93-L) gets re-energized when the main bulk of the upper trough over eastern North America moves into the ocean and phases with the upper vortex (with eastern divergence of the re-energized upper vortex also contributing to the pressure falls).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across favorable 28 to 29 deg C waters.

24 Hr Forecast (0000Z Sep 16)...Tropical low south-southwest of the Republic of Cabo Verde...centered at 10N-25.5W

48 Hr Forecast (0000Z Sep 17)...40 mph maximum sustained wind tropical storm centered at 11N-29.5W

72 Hr Forecast (0000Z Sep 18)...60 mph maximum sustained wind tropical storm centered at 12N-33.5W

96 Hr Forecast (0000Z Sep 19)...80 mph maximum sustained wind hurricane centered at 13.5N-37W

120 Hr Forecast (0000Z Sep 20)...100 mph maximum sustained wind hurricane centered at 15N-40.5W

2015 Atlantic Hurricane Season Birdseye Discussion #87

By: NCHurricane2009, 7:06 AM GMT on September 14, 2015

...MONDAY SEPTEMBER 14 2015 3:05 AM EDT...
Satellite imagery shows that the vigorous eastern Atlantic tropical wave has rapidly produced a well-organized tropical low pressure spin in the Intertropical Convergence Zone (ITCZ)...and this new low pressure spin has been upgraded to Invest 93-L on the Naval Research Laboratory site of the US Navy. The most recent satellite frames early this morning suggest a tropical cyclone maybe already forming..and therefore a tropical depression or tropical storm could be declared at any time today. See special feature section below for additonal details on 93-L. If the current rapid organization trends continue...it is possible that 93-L strengthens even more than shown in the forecast presented in the special feature section. In the long-range...93-L is expected to turn northward and avoid the Caribbean.

Satellite imagery also shows another vigorous tropical wave has emerged from western Africa and into the eastern tropical Atlantic...but has not become better organized relative to yesterday. However atmospheric and thermodynamic conditions are quiet favorable for additional development of this tropical wave...and there continues to be computer model support suggesting that this wave will develop. Therefore this tropical wave remains a special feature on this blog. See second special feature section below for additional details on this system.

A large area of showers and thunderstorms currently spans the Gulf of Mexico..Florida Peninsula...the northwestern Bahamas...and western Atlantic...all in association with the tail end of the surface cold front of the vigorous eastern North America surface frontal system and upper trough. Currently a shortwave upper trough over the central US is diving southeastward on the back side of the upper trough...which over the next three days will be left behind as a cut-off southeastern US upper trough with some favorable upper ridging developing ahead of (south and east of) the cut-off. Therefore activity along the decaying tail end of the surface cold front is likely to linger in this region with the support of upper divergence on the east side of the forecast cut-off upper trough...with potential for some tropical development if some of this activity organizes below some of the favorable upper ridging. Indeed this is already the case tonight where strong thunderstorms in the western Gulf of Mexico have organized into tropical surface low Invest 94-L below the upper ridging...see third special feature section below for more info on 94-L. Will also watch the remainder of the decaying tail end of the front which extends into the western Atlantic.

The 1016 mb surface low in the open ocean (located at 30N-42.5W during the previous discussion) has weakened into a disorganized surface trough. Therefore this feature no longer has potential for tropical development.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1932Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL WAVE INVEST 93-L...
Current Prognosis...The vigorous tropical wave in the eastern tropical Atlantic has rapidly developed a well-organized surface low pressure spin within the ITCZ (Intertropical Convergence Zone) in the last 24 hours...and as a result I have moved up the time of forecast tropical cyclone formation to 0000Z Sep 15 (tomorrow night). This surface low pressure spin has been upgraded to disturbance Invest 93-L on the Naval Research Laboratory (NRL) site of the US Navy. As of 0000Z earlier this evening 93-L was centered at 11N-36W...which is further west than I previously forecasted for tonight. This is not to suggest that the tropical wave is moving faster to the west than previously thought...but instead satellite animation simply showed the tropical wave formed a center of low pressure further to the west...with this low pressure moving about as fast as the parent tropical wave has been moving. Therefore my updated forecast track is initially a westward adjustment with the same approximate 5W longitude per day speed as shown in previous forecasts.

Atmospheric Outlook for the Forecast Period...The TUTT (Tropical Upper Tropospheric Trough) that sheared apart Grace a few days ago (marked by pair of blue Ls to the northwest of 93-L in the above atmospheric features chart) has weakened and lifted northward...allowing the favorable low shear/enhanced upper outflow envionment of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag line in the lower-right of the above atmopsheric features chart) to expand in its wake. Therefore upper-level winds are going to be quiet favorable for tropical development early in the forecast period. 93-L is expected to track westward under the influence of the surface 1027 mb Atlantic subtropical ridge for the first 48 hours. Afterwards..a large area of surface pressure falls to the south of the surface ridge (from the Gulf of Mexico all the way into the western Atlantic) will turn 93-L northward...causing 93-L to weaken from peak intensity while entering unfavorable westerly shear on the southeast side of the TUTT. This large region of surface pressure falls will be induced by upper divergence on the east side of a southeastern US cut-off upper trough and decaying surface frontal boundary to be left behind by the large frontal system currently over eastern North America...and as the TUTT gets re-energized when the main bulk of the upper trough over eastern North America moves into the ocean and phases with the TUTT by 72 hours (with eastern divergence of the re-energized TUTT also contributing to the pressure falls).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across very favorable 29 deg C waters.

24 Hr Forecast (0000Z Sep 15)...40 mph maximum sustained wind tropical storm centered at 12N-41W

48 Hr Forecast (0000Z Sep 16)...60 mph maximum sustained wind tropical storm centered at 13.5N-45W

72 Hr Forecast (0000Z Sep 17)...75 mph maximum sustained wind hurricane centered at 16N-47W

96 Hr Forecast (0000Z Sep 18)...50 mph maximum sustained wind tropical storm centered at 21N-47W

120 Hr Forecast (0000Z Sep 19)...35 mph maximum sustained wind tropical depression centered at 25N-47W

...SPECIAL FEATURE...TROPICAL WAVE EMERGING FROM AFRICA...
Current Prognosis...Meteosat-9 infrared satellite imagery suggests a vigorous tropical wave with a large field of cloudiness and thunderstorms has emerged from the west coast of Africa into the eastern tropical Atlantic...but has not become better organized. I estimate that as of 0000Z the tropical wave axis was approximately at 18W longitude...which is 2E longitude of where I predicted it would be tonight. Therefore all of my forecast points below have been adjusted by 2E. The forecast track shows an increasing slow down in the track and an increasing bend to the north due to the south side of the steering ridge becoming eaten away due to the forecast development of Invest 93-L to the west into a tropical cyclone coupled with dropping surface pressures south of the ridge from the Gulf of Mexico all the way toward 93-L (see atmospheric outlook section below for more details on the development of the dropping surface pressures).

Atmospheric Outlook for the Forecast Period...Upper-level winds will be very favorable for the development of this tropical wave due to the low shear and enhanced upper outflow of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag line in the lower-right of the above atmopsheric features chart). This system will be steered westward by the 1027 mb Atlantic surface ridge through the forecast period. However the westward track will be slowing and bending increasingly northward as the south side of the ridge becomes eaten away due to dropping surface pressures south of the ridge from the Gulf of Mexico to the western Atlantic. This large region of surface pressure falls will be induced by upper divergence on the east side of a southeastern US cut-off upper trough and decaying surface frontal boundary to be left behind by the large frontal system currently over eastern North America...and as a cut-off upper vortex (marked by pair of blue Ls northwest of 93-L) gets re-energized when the main bulk of the upper trough over eastern North America moves into the ocean and phases with the upper vortex (with eastern divergence of the re-energized upper vortex also contributing to the pressure falls).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across favorable 28 to 29 deg C waters.

24 Hr Forecast (0000Z Sep 15)...Tropical low south of the Republic of Cabo Verde centered at 11.5N-24.5W

48 Hr Forecast (0000Z Sep 16)...Tropical low centered at 12.5N-29.5W

72 Hr Forecast (0000Z Sep 17)...40 mph maximum sustained wind tropical storm centered at 13.5N-33.5W

96 Hr Forecast (0000Z Sep 18)...60 mph maximum sustained wind tropical storm centered at 14.5N-37.5W

120 Hr Forecast (0000Z Sep 19)...80 mph maximum sustained wind hurricane centered at 16N-41W

...SPECIAL FEATURE...TROPICAL LOW INVEST 94-L...
Current Prognosis...A stationary surface tropical low centered at 22N-97W has developed in the western Gulf of Mexico from strong thunderstorms that occurred at the tail end of the cold front of the eastern North America frontal system and associated upper trough. The thunderstorms in this new tropical low have weakened...but with this system expected to stay stationary over the next 48 hours in favorable atmospheric and thermodynamic conditions outlined below...there is a good chance of tropical cyclone formation and this system is upgraded to a special feature on this blog. I forecast tropical cyclone formation at 48 hours instead of in the next 24 hours to account for the current lack of thunderstorm activity.

Atmospheric Outlook for the Forecast Period...Upper wind forecasts indicate that 94-L will be on the north side of upper ridging (marked by blue-zig-zag line just south of 94-L in the above atmopsheric features chart) through the forecast period. Therefore 94-L will be in favorable low shear/enhanced outflow beneath the upper ridge...perhaps with periods of light westerly shear due to the zonal upper westerlies that are occuring on the north side of the upper ridge. Current assumption is the westerly shear will not be strong enough to stop this system from developing further. A 1021 mb surface ridge is present over the eastern US...which suggests that 94-L should be moving westward while steered by the ridge. However satellite animation shows 94-L is stationary...and the National Hurricane Center (NHC) tropical weather outlook states that 94-L should be stationary over the next 48 hours. The red-zig-zag line extending from the 1021 mb center in the above atmospheric features chart shows that a blocking lobe of this surface ridge extends into northeastern Mexico which is why 94-L is stationary. The NAVGEM model surface pressure animation lines up with the NHC tropical weather outlook statement...showing this blocking lobe finally moving out of the way after 48 hours (after 0000Z September 16...when the 1021 mb ridge...supported by upper convergence on the back side of the upper trough over eastern North America...moves eastward into the Atlantic with the upper trough). This will cause 94-L to move northwestward into northeastern Mexico on the southwest side of the 1021 mb ridge after 48 hours.

Thermodynamic Outlook for the Forecast Period...The above thermodynamic chart shows 94-L is in a very favorable thermodynamic picture for tropical development while in the midst of a moist air mass and over richly warm 30 to 31 deg C waters.

24 Hr Forecast (0000Z Sep 15)...Surface low centered at 22N-97W

48 Hr Forecast (0000Z Sep 16)...35 mph maximum sustained wind tropical depression centered at 22N-97W

72 Hr Forecast (0000Z Sep 17)...45 mph maximum sustained wind tropical storm approaching landfall in northeastern Mexico...centered at 22.5N-97.6W

96 Hr Forecast (0000Z Sep 18)...Remnant low centered inland but near the coast of northeastern Mexico...at 23.5N-98.1W

2015 Atlantic Hurricane Season Birdseye Discussion #86

By: NCHurricane2009, 4:35 AM GMT on September 13, 2015

...SUNDAY SEPTEMBER 13 2015 12:35 AM EDT...
The remnant tropical wave of former Tropical Storm Grace as expected has lost thunderstorms as it slides below unfavorable upper-level convergence below an upper vortex over the central Caribbean Sea (marked as a blue L to the left of Grace in the atmospheric features chart below). Therefore this tropical wave is likely to be dropped from the National Hurricane Center tropical weather outlook at any time.

Satellite imagery shows that the vigorous eastern Atlantic tropical wave is re-organizing along the Intertropical Convergence Zone (ITCZ). With atmospheric and thermodynamic conditions very favorable for development in this region over the next few days...this system is likely to become a tropical cyclone. See special feature section below for additional details. In the long-range...any tropical cyclone that develops from this tropical wave is more likely to turn north and avoid the Caribbean Sea.

Satellite imagery also shows another vigorous tropical wave currently over western Africa has become better organized while approaching the eastern tropical Atlantic. The GFS and European (ECMWF) models suggest potential for this tropical wave to develop. Given the model support and increasing organization of the wave...this tropical wave has been upgraded to a special feature on this blog. See second special feature section below for additional details on this tropical wave.

A large area of showers and thunderstorms currently spans the Gulf of Mexico..the southeastern US...and western Atlantic...all in association with the tail end of the surface cold front of the currently vigorous eastern North America surface frontal system and upper trough. Over the next four days...the upper trough is forecast to leave behind a cut-off upper trough over the southeastern US with some favorable upper ridging developing ahead of (south and east of) the cut-off. Therefore activity along the decaying tail end of the surface cold front is likely to linger in this region with the support of upper divergence on the east side of the forecast cut-off upper trough...with potential for some tropical development if some of this activity organizes below some of the favorable upper ridging. All previous computer models that previously showed western Gulf of Mexico development from this activity continue to no longer show such a solution...but will continue to watch the Gulf of Mexico and western Atlantic region over the next few days.

The 1016 mb surface low in the open ocean...currently located at 30N-42.5W...has not become better organized. As this surface low continues westward in the mid-latitudes on the south side of the 1026 mb Atlantic surface ridge...it certainly has potential for tropical cyclone formation even though none of the computer models currently predict this. This is because a high-latitude upper ridge (marked by blue H in the top-right of the atmopsheric features chart below) has developed over the last four days due to southerly warm air advection ahead of the strong frontal system over eastern North America...and this surface low will be in favorable low shear and enhanced outflow on the south and west sides of the high-latitude upper ridge over the next 72 hours. After that time...tropical cyclone formation will no longer be possible as the surface low becomes absorbed by the aformentioned frontal system as the frontal system moves into the north-central Atlantic by that time. If this surface low organizes further before my next full blog update...I will be issuing a special update on this blog to declare the surface low as a special feature.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1930Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...EASTERN ATLANTIC TROPICAL WAVE...
Current Prognosis...As of 0000Z the tropical wave was located along 27.5W longitude with the associated thunderstorms increasing but becoming part of a larger east-west band of thunderstorms along the intertropical convergence zone (ITCZ) that extends all the way toward 42.5W longitude. The increase in the tropical wave's thunderstorms and nearby ITCZ thunderstorms is due to enhanced poleward upper outflow supplied by upper ridging in the eastern tropical Atlantic (marked by blue zig-zag line in the lower-right of the above atmopsheric features chart). Because this tropical wave does not yet have a distinct low pressure circulation within the ITCZ...my updated forecast below delays tropical cyclone formation till 0000Z September 17 because this system will take some time to develop a circulation seperate from the broad and currently active ITCZ in the area. Then after that time I forecast brisk development in the favorable atmospheric and thermodynamic conditions outlined below.

Atmospheric Outlook for the Forecast Period...The TUTT (Tropical Upper Tropospheric Trough) that sheared apart Grace a few days ago (marked by blue L and blue-dashed line in the lower-right of the atmospheric features chart above) is in the process of weakening and lifting northward while the favorable low shear/enhanced upper outflow envionment of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag lines also in the lower-right of the above atmopsheric features chart) is expanding in its wake. Therefore upper-level winds are going to be quiet favorable for tropical development through the forecast period. This system is expected to track westward under the influence of the surface 1026 mb Atlantic subtropical ridge for the first 72 hours. By the end of the forecast period...a large area of surface pressure falls to the south of the surface ridge is expected to develop from the Gulf of Mexico all the way into the western Atlantic which will cause the track to bend more northwestward. This large region of surface pressure falls will be induced by upper divergence on the east side of a southeastern US cut-off upper trough and decaying surface frontal boundary to be left behind by the large frontal system currently over eastern North America...and as the aforementioned TUTT gets re-energized when the main bulk of the upper trough over eastern North America moves into the ocean and phases with the TUTT by 96 hours (with eastern divergence of the re-energized TUTT also contributing to the pressure falls).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across very favorable 29 deg C waters. Moreover...the most recent thermodynamic chart above suggests that the dry saharan air (seen in the bottom-center of the chart) has weakened relative to the timeframe of previous cyclones Fred and Grace. In addition...with the observations of this tropical wave organizing further south in the ITCZ (Intertropcal Convergence Zone)...this system during its formative stages is likely to stay south of whatever dry saharan air is left...and therefore the current assumption is that dry air will not be a problem for this system.

24 Hr Forecast (0000Z Sep 14)...Tropical wave at 32.5W longitude

48 Hr Forecast (0000Z Sep 15)...Tropical low centered at 10N-37.5W

72 Hr Forecast (0000Z Sep 16)...Tropical low centered at 11N-42.5W

96 Hr Forecast (0000Z Sep 17)...40 mph maximum sustained wind tropical storm centered at 12.5N-46.5W

120 Hr Forecast (0000Z Sep 18)...60 mph maximum sustained wind tropical storm centered at 15.5N-47.5W

...SPECIAL FEATURE...WESTERN AFRICA TROPICAL WAVE...
Current Prognosis...Satellite imagery suggests a tropical wave over interior western Africa has moved from 3W to 12.5W longitude over the last 24 hours while developing more thunderstorms and becoming better organized. The forecast track below is based on the initial rapid westward motion observed over the last 24 hours...followed by a slow down in the track as the steering easterlies on the south side of the Atlantic surface ridge weaken due to the forecast development of the adjacent eastern Atlantic tropical wave to the west into a tropical cyclone and due to dropping surface pressures south of the ridge from the Gulf of Mexico all the way toward the adjacent tropical cyclone (see atmospheric outlook section below for more details on the development of the dropping surface pressures).

Atmospheric Outlook for the Forecast Period...Upper-level winds will be favorable for the development of this tropical wave due to the low shear and enhanced upper outflow of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag line in the lower-right of the above atmopsheric features chart). This system will be steered westward by the 1026 mb Atlantic surface ridge through the forecast period. However the westward track will be slowing as the steering easterlies on the south side of the ridge weaken due to dropping surface pressures south of the ridge from the Gulf of Mexico to the western Atlantic. This large region of surface pressure falls will be induced by upper divergence on the east side of a southeastern US cut-off upper trough and decaying surface frontal boundary to be left behind by the large frontal system currently over eastern North America...and as a cut-off upper vortex gets re-energized when the main bulk of the upper trough over eastern North America moves into the ocean and phases with the upper vortex (with eastern divergence of the re-energized upper vortex also contributing to the pressure falls).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across favorable 28 to 29 deg C waters. It is currently assumed that the dry saharan air that lies ahead (seen in the bottom-center of the above thermodynamics chart) will be moistened out by the forecast development of the adjacent eastern Atlantic tropical wave. Therefore it is currently assumed dry air will not be a problem for this system.

24 Hr Forecast (0000Z Sep 14)...Tropical wave southeast of the Republic of Cabo Verde at 20.5W longitude

48 Hr Forecast (0000Z Sep 15)...Tropical low south-southwest of the Republic of Cabo Verde centered at 11.5N-26.5W

72 Hr Forecast (0000Z Sep 16)...Tropical low centered at 12.5N-31.5W

96 Hr Forecast (0000Z Sep 17)...40 mph maximum sustained wind tropical storm centered at 13.5N-35.5W

120 Hr Forecast (0000Z Sep 18)...60 mph maximum sustained wind tropical storm centered at 14.5N-39.5W

2015 Atlantic Hurricane Season Birdseye Discussion #85

By: NCHurricane2009, 8:21 AM GMT on September 12, 2015

...SATURDAY SEPTEMBER 12 2015 4:20 AM EDT...
Special statement: With the dissipation of Henri into a remnant low...there are currently no active tropical cyclones in the Atlantic basin. However there are several areas of interest and therefore the following introduction is split into two sections:

...SECTION 1: CONCERNING THE TROPICAL BELT OF THE ATLANTIC BASIN...
The remnant tropical wave of former Tropical Storm Grace has seen a significant increase in thunderstorms while moving across the Lesser Antilles...Puerto Rico...the Virgin Islands...and eastern Caribbean Sea. This is due to the remnant wave reaching an area of supportive upper-level divergence on the east side of an upper vortex over the central Caribbean (marked as a blue L to the left of Grace in the atmospheric features chart below). Over the next 24 to 48 hours...the remnant wave will be sliding directly below the upper vortex...which should cause the thunderstorms to weaken due to upper-level convergence and sinking motion of the air directly below and on the west side of the upper vortex.

Even though thunderstorms have dissipated in association with the vigorous tropical wave that has entered the eastern tropical Atlantic from western Africa...the most recent satellite frames early this morning suggest the tropical wave is re-organizing at a further southwest location along the Intertropical Convergence Zone (ITCZ). With atmospheric and thermodynamic conditions very favorable for development in this region over the next few days...this system still has potential for tropical cyclone formation. See special feature section below for additional details. In the long-range...any tropical cyclone that develops from this tropical wave is more likely to turn northwest and avoid the Caribbean Sea.

...SECTION 2: CONCERNING THE MID-LATITUDES OF THE ATLANTIC BASIN...
A large area of thunderstorms currently spans northeastern Mexico...the northern Gulf of Mexico..and the southeastern US...and will soon expand across the Florida peninsula and into the western Bahamas and western Atlantic over the next few days...all in association with the tail end of the surface cold front of the currently vigorous eastern North America surface frontal system and upper trough. Over the next five days...the upper trough is forecast to leave behind a cut-off upper trough over the southeastern US with some favorable upper ridging developing ahead of (south and east of) the cut-off. Therefore activity along the decaying tail end of the surface cold front is likely to linger in this region with the support of upper divergence on the east side of the forecast cut-off upper trough...with potential for some tropical development if some of this activity organizes below some of the favorable upper ridging. All previous computer models that previously showed western Gulf of Mexico development from this activity continue to no longer show such a solution...but will continue to watch the Gulf of Mexico and western Atlantic region over the next few days.

While fast accelerating northward toward southeastern Newfoundland...Tropical Storm Henri has lost its closed circulation and is no longer classified as a tropical cyclone. The reason the circulation opened up to the west is due to the low pressure field of the surface fronts incoming from the west (associated with the eastern North America frontal system mentioned in the previous paragraph) which was equally as strong as Henri's low pressure field. The remnant of Henri may produce some gusty showers or thunderstorms over southeastern corner of Newfoundland early this morning prior to fully losing its identity along the incoming frontal zone later today.

An analysis of the mid-latitudes over past few days suggests that the new 1016 mb surface low mentioned in the NHC tropical weather outlook...located far southwest of the Azores and currently centered at 28N-40W...has developed along the same low-level east-west trough that Henri developed from. It appears an upper divergence maximum on the east side of the TUTT (Tropical Upper Tropospheric Trough) that sheared apart Grace a few days ago (marked by blue L and blue-dashed line in the lower-right of the atmospheric features chart below) aided in the formation of this surface low in what was left of the east-west low-level trough. As this surface low moves westward in the mid-latitudes on the south side of the 1025 mb Atlantic surface ridge...it certainly has potential for tropical cyclone formation even though none of the computer models currently predict this. This is because a high-latitude upper ridge (marked by blue H in the top-center of the above atmopsheric features chart) has developed over the last three days due to southerly warm air advection ahead of the strong frontal system over eastern North America...and this surface low will be in favorable low shear and enhanced outflow on the south and west sides of the high-latitude upper ridge over the next 96 hours. After that time...tropical cyclone formation will no longer be possible as the surface low becomes absorbed by the aformentioned frontal system as the frontal system moves into the north-central Atlantic by that time. If this surface low organizes further later this morning...I will be issuing a special update on this blog to declare the surface low as a special feature.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1925Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...EASTERN ATLANTIC TROPICAL WAVE...
Current Prognosis...Meteosat-9 infrared satellite imagery suggests that the thundestorm activity of the vigorous tropical wave emerging from western Africa into the easern tropical Atlantic essentially dissipated over the last 24 hours while moving toward 25W longitude as of 0000Z earlier this evening. However the most recent satellite frames after 0000Z suggest the tropical wave maybe re-organizing further southwest...toward an area of organizing thunderstorms along the intertropical convergence zone (ITCZ) located at 7.5N-30W. Therefore my updated forecast below is adjusted accordingly...showing re-organization of this system to the southwest toward the aforementioned ITCZ activity over the next 48 hours...followed by forecast tropical cyclone formation and brisk development at 72 hours and beyond in the favorable atmospheric and thermodynamic conditions outlined below.

Atmospheric Outlook for the Forecast Period...The TUTT (Tropical Upper Tropospheric Trough) that sheared apart Grace a few days ago (marked by blue L and blue-dashed line in the lower-right of the atmospheric features chart above) is in the process of weakening and lifting northward while the favorable low shear/enhanced upper outflow envionment of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag lines also in the lower-right of the above atmopsheric features chart) is expanding in its wake. Therefore upper-level winds are going to be quiet favorable for tropical development through the forecast period. This system is expected to track westward under the influence of the surface 1025 mb Atlantic subtropical ridge for the first 96 hours. By the end of the forecast period...a large area of surface pressure falls to the south of the surface ridge is expected to develop from the Gulf of Mexico all the way into the western Atlantic which will cause the track to bend more northwestward. This large region of surface pressure falls will be induced by upper divergence on the east side of a southeastern US cut-off upper trough and decaying surface frontal boundary to be left behind by the large frontal system currently over eastern North America...and as the aforementioned TUTT gets re-energized when the main bulk of the upper trough over eastern North America moves into the ocean and phases with the TUTT by 120 hours (with eastern divergence of the TUTT also contributing to the pressure falls).

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across very favorable 29 deg C waters. Moreover...the most recent thermodynamic chart above suggests that the dry saharan air (seen in the bottom-center of the chart) has weakened relative to the timeframe of previous cyclones Fred and Grace. In addition...with the observations of this tropical wave re-organizing further south in the ITCZ (Intertropcal Convergence Zone)...this system during its formative stages is likely to stay south of whatever dry saharan air is left...and therefore the current assumption is that dry air will not be a problem for this system.

24 Hr Forecast (0000Z Sep 13)...Tropical wave at 30W longitude with vorticity maximum along 8N latitude

48 Hr Forecast (0000Z Sep 14)...Tropical low centered at 9N-35W

72 Hr Forecast (0000Z Sep 15)...35 mph maximum sustained wind tropical depression centered at 10N-40W

96 Hr Forecast (0000Z Sep 16)...50 mph maximum sustained wind tropical storm centered at 11N-45W

120 Hr Forecast (0000Z Sep 17)...65 mph maximum sustained wind tropical storm centered at 12.5N-48W

2015 Atlantic Hurricane Season Birdseye Discussion #84

By: NCHurricane2009, 5:26 AM GMT on September 11, 2015

...FRIDAY SEPTEMBER 11 2015 1:26 AM EDT...
A vigorous tropical wave is emerging from the west coast of Africa into the Atlantic tropics and has potential to strengthen while moving across the central tropical Atlantic. See second special feature section below for additional details on this tropical wave. Just after five days...the upper trough currently over eastern North America will have moved into the ocean and has potential to phase with and re-energize the TUTT (Tropical Upper Tropospheric Trough) mentioned in the atmospheric outlook of the special feature section. In turn upper divergence on the east side of the re-energized TUTT has the potential to create an area of dropping surface pressures to the south of the Atlantic subtropical ridge...in which case in the long-range this system would turn northeast and avoid the Caribbean while turning into the area of dropping pressures.

Tropical Storm Henri accelerates northward in the northwestern Atlantic and toward southeastern Newfoundland. However by the time Henri reaches Newfoundland it will have transitioned into a non-tropical remnant low. See Henri special feature section below for additional details...and continue to visit www.nhc.noaa.gov for up-to-the-minute latest information on Henri.

Over the next four days...the tail end of the cold front associated with the 1001 mb eastern North America frontal cyclone will settle into the western Gulf of Mexico. It was previously forecast that the base of the associated upper trough would evolve into a cut-off upper vortex over Texas...with eastern divergence of cut-off upper vortex triggering a subtropical or tropical disturbance along the front. The usually conservative European (ECMWF) model was the largest proponent of this scenario...but has now backed off this solution along with the other models. Therefore this scenario appears less likely to occur than previously thought.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1931Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM HENRI...
Current Prognosis...After being stationary for two days...Henri is accelerating northward after a southerly steering current has developed between the 1023 mb Atlantic ridge to the east and 1001 mb frontal cyclone to the west incoming from eastern North America. As of 0000Z satellite imagery suggested the center of Henri passed over 34.8N-60.7W while continuing northward. The tropical storm continues to largely be supported by upper divergence on the east side of a shortwave upper trough near Bermuda (marked by a blue-dashed line immediately left of Henri in the above atmospheric features chart). The upper trough continues to suppress storm activity west of the center...continuing to expose the center of circulation as a low-level cloud swirl located southwest of the circulation's thunderstorm activity.

Atmospheric Outlook for the Forecast Period...Henri is currently embedded in deep-layered southerly flow at all layers of the atmosphere...to the west of a high-latitude upper ridge and 1023 mb Atlantic surface ridge...and to the east of the 1001 mb frontal cyclone and its upper trough to the west incoming from eatsern North America. The cold front of the frontal cyclone will progress offshore and absorb Henri in the next 24 hours...transitioning Henri to non-tropical.

Thermodynamic Outlook for the Forecast Period...Although this system is currently over favorable 28 deg C waters...in the next 24 hours it will cross the 26 deg C isotherm into cooler waters by 48 hours which will aid in the transition to non-tropical.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 12)...45 mph maximum sustained wind tropical storm centered at 42N-59W...transitioning to non-tropical

Track Forecast...Henri has been in a straightforward steering situation with very small errors in previous forecast tracks. Therefore there are no changes to the track forecast tonight.

Intensity Forecast...As noted in the above atmopsheric outlook section...Henri is embedded in deep-layered southerly flow in all layers...including in the upper atmopsheric layer. Despite the upper wind vector being southerly...Henri is under reduced shear as expected because the circulation has also accelerated northward and is more or less matching the upper-level southerly wind vector. However Henri has not strengthened despite the reduced shear...perhaps because the upper shortwave near Bermuda (mentioned in the above current prognosis) is too close to the circulation of Henri. Therefore my updated intensity forecast (as well as the NHC's) is lower than the previous while only showing slight strengthening in the next 24 hours...but it is conceivable that Henri never strengthens at all.

Impact Forecast...Impact swath is an extrapolation of the 11 PM EDT tropical storm wind field along the forecast track. It is possible that after 24 hrs and before 48 hours that the non-tropical remnant of Henri could deliver some gale force winds to southeastern Newfoundland...especially since the non-tropical remnant could be slow to weaken while supported by divergence on the east side of the upper trough associated with the incoming frontal cyclone. But because Henri has not really strengthened...it is now much more likely that non-tropical Henri will barely be of gale force as he passes by southeastern Newfoundland in which case Henri will not be a noteworthy event for southeastern Newfoundland.

...SPECIAL FEATURE...WESTERN AFRICA TROPICAL WAVE...
Current Prognosis...Meteosat-9 infrared satellite imagery suggests that the thunderstorm activity of the tropical wave over western Africa has weakened a bit as it emerges into the tropcial Atlantic...but has progressively been organizing into a large-broad tropical low pressure circulation centered at approximately 12N-18W. This is a bit northeast of where I predicted the circulation would be and therefore I have adjusted the forecast track accordingly and slowed the forecast westward pace of the system to 5-W longitude per day.

Atmospheric Outlook for the Forecast Period...Through the forecast period the 1023 mb Atlantic surface ridge will steer this system westward. In the upper-layers...the TUTT (Tropical Upper Tropospheric Trough) that sheared apart Grace (marked by pair of blue Ls to the northeast of Grace and east of Henri in the above atmospheric features chart) will weaken and lift northward while the favorable low shear/enhanced upper outflow envionment of the eastern tropical Atlantic upper ridge (marked by blue-zig-zag line and blue H in the lower-right portion of the above atmospheric features chart) expands in its wake. Because the updated track forecast now keeps this system from running into the receding TUTT...this system is now expected to be under the favorable expanding upper ridge through the forecast period. However instead of forecasting tropical cyclone formation sooner in lieu of the more favorable upper wind forecast...instead I decided to maintain tropical cyclone formation at the timeframe that is now 72 hrs away and I have lowered my intensity forecast because this system is taking on a large-broad structure that will take some time to consolidate into a tropical cyclone.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across very favorable 28 to 29 deg C waters. Moreover...the most recent thermodynamic chart above suggests that the dry saharan air (seen in the bottom-center of the chart) has weakened relative to the timeframe of previous cyclones Fred and Grace. With the dry air being overall weaker...with low vertical shear expected during the forecast period (which will lessen the chances of dry air getting driven into the circulation)...and with warm waters helping to drive instability for thunderstorms...my current assumption is that dry air won't be as much of a problem for this system as it was for Fred and Grace. With this assumption and with the favorable upper wind forecast in the above atmo outlook section...I still forecast some brisk development by the end of the forecast period.

24 Hr Forecast (0000Z Sep 12)...Tropical low centered south of the Republic of Cabo Verde at 12.5N-23W

48 Hr Forecast (0000Z Sep 13)...Tropical low centered southwest of the Republic of Cabo Verde at at 13N-28W

72 Hr Forecast (0000Z Sep 14)...35 mph maximum sustained wind tropical depression centered at 13.5N-33W

96 Hr Forecast (0000Z Sep 15)...45 mph maximum sustained wind tropical storm centered at 14N-38W

120 Hr Forecast (0000Z Sep 16)...65 mph maximum sustained wind tropical storm centered at 14.5N-43W

2015 Atlantic Hurricane Season Birdseye Discussion #83

By: NCHurricane2009, 5:27 AM GMT on September 10, 2015

...THURSDAY SEPTEMBER 10 2015 1:30 AM EDT...
Tropical Depression Grace as expected weakens to a remnant surface trough in the central tropical Atlantic while continuing to struggle with dry saharan air and westerly vertical shear. This is my final statement on Grace on this blog.

Satellite imagery shows that the tropical wave over western Africa has considerably re-strengthened and re-organized while approaching the west coast of Africa...with computer model support for the tropical wave returning. Therefore this tropical wave has been upgraded to a special feature on this blog. Unlike Grace...this system has potential to strengthen instead of weaken while moving across the central tropical Atlantic. See second special feature section below for additional details on this tropical wave.

Tropical Depression Eight east-southeast of Bermuda strengthens into Tropical Storm Henri. Henri is expected to move northward across the northwest Atlantic and toward Newfoundland over the next three days. Interests in the northwest Atlantic should continue to monitor Henri closely. By the time Henri reaches Newfoundland it will have transitioned into a non-tropical remnant low...but depending on how strong Henri gets as a tropical system before the transition it could bring gale force winds to southeastern Newfoundland in two to three days. See Henri special feature section below for additional details...and continue to visit www.nhc.noaa.gov for up-to-the-minute latest information on Henri.

Over the next five days...cool air advection behind the 988 mb eastern North America frontal cyclone (seen in top-left of the above atmopsheric features chart below) will deliver a longwave upper trough into the central US...with subsequent shortwave upper troughs diving southeastward on the back side of the longwave. By the end of five days an upper ridge will develop over the western US...potentially causing some of this shortwave energy to evolve into a cut-off upper vortex over Texas. Depending on where exactly the tail end of the surface front ends up in the Gulf of Mexico in relation to the forecast cut-off upper vortex depends on whether or not eastern divergence of cut-off upper vortex triggers a subtropical or tropical disturbance along the front in the western Gulf of Mexico by next week. The usually conservative European (ECMWF) model continues to be the biggest proponent in predicting tropical cyclone formation in this scenario while the GFS continues to not show a cut-off upper vortex forming over Texas and hence predicts no tropical or subtropical development. Interests in the western Gulf of Mexico...coastal Louisiana...and coastal Texas should carefully monitor this situation in case the European (ECMWF) model scenario unfolds.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1929Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM HENRI...
Current Prognosis...Tropical Depression Eight located east-southeast of Bermuda has strengthened to Tropical Storm Henri while continuing to be supported by upper divergence on the east side of a shortwave upper trough over Bermuda that has recently amplified into an upper vortex (marked by blue L immediately left of Henri in the above atmospheric features chart). Strong thunderstorms have been associated with this tropical cyclone all day...but remain biased to the east of the center due to westerly shear imparted by the upper vortex. This westerly shear is why this system is only slowly strengthening despite the presence of strong thunderstorms. As of 0000Z satellite imagery suggested the center of Henri was pinwheeling stationary while centered at 31N-61W.

Atmospheric Outlook for the Forecast Period...Henri has been stationary while trapped between two surface ridges marked in the above atmopsheric features chart...one 1021 mb ridge norteast of the system and a 1018 mb ridge to the southwest of the system. This is about to change however because the 988 mb frontal cyclone over eastern North America (seen in top-left of the above atmopsheric features chart) is in the process of knocking out the 1021 mb ridge...which will soon cause Henri to accelerate northward in the southerly flow on the east side of the frontal cyclone. Upper-level winds are expected to become more favorable for Henri in the 24 to 48 hour timeframe...when warm air advection ahead of the aforementioned frontal cyclone develops a high-latitude upper ridge south of Atlantic Canada that shifts the unfavorable Bermuda upper vortex westward and away (this upper ridge is already starting as marked by a blue H due north of Henri). But just after 48 hours...Henri will be merging with the cold front associated with the incoming frontal cyclone...transitioning it to non-tropical.

Thermodynamic Outlook for the Forecast Period...This system will be initially stationary over favorable 28 deg C waters...and then cross the 26 deg C isotherm into cooler waters by 48 hours which will aid in the transition to non-tropical by that time.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 11)...45 mph maximum sustained wind tropical storm centered at 35N-61W

48 Hr Forecast (0000Z Sep 12)...50 mph maximum sustained wind tropical storm centered at 42N-59W...transitioning to non-tropical

Track Forecast...I have essentially made no changes to my track forecast on this system since the previous discussion.

Intensity Forecast...I initially predicted that this tropical cyclone would peak at 50 mph winds before transition to non-tropical in discussion #81. Due to the strong thunderstorms and earlier-than-forecast tropical cyclone formation...last night in discussion #82 I had bumped up the forecast peak intensity to 60 mph. It has become clear that the upper vortex over Bermuda has had an oppressive effect on Henri as I initially surmised would be the case during discussion #81...and therefore I have essentially reverted back to the weaker intensity forecast from discussion #81.

Impact Forecast...Impact swath is an extrapolation of the 11 PM EDT tropical storm wind field along my forecast track. It is possible that after 48 hrs and before 72 hours that the non-tropical remnant of Henri could deliver some gale force winds to southeastern Newfoundland...especially since the non-tropical remnant could be slow to weaken while supported by divergence on the east side of the upper trough associated with the incoming frontal cyclone.

...SPECIAL FEATURE...WESTERN AFRICA TROPICAL WAVE...
Current Prognosis...Meteosat-9 infrared satellite imagery suggests that the tropical wave over western Africa has rapidly intensified and re-organized while moving from approximately 7.5W to 14W in last 24 hrs. Although this 24-hourly motion is low-confidence because the tropical wave was so weak and poorly-defined on satellite 24 hours ago...my forecast track below is based on this 24-hourly westward progression and the fact that the tropical wave's vorticity maximum appears to be at around 11N latitude based on the organizaiton in the thunderstorm clouds.

Atmospheric Outlook for the Forecast Period...Thru the forecast period the 1021 mb Atlantic surface ridge will steer this system westward. I initially assumed that the tropical wave will continue to organize into a tropical low over the next 24 hours while the tropical wave moves into a favorable low shear/enhanced upper outflow environment beneath the tropical upper ridge in the eastern Atlantic (marked by blue-zig-zag line and blue Hs in the lower-right portion of the above atmospheric features chart). However at 48 and 72 hours I show no additional development as current upper wind forecasts indicate that this system will run into vertical westerly shear imparted by the upper trough that has recently sheared apart Grace (this upper trough is marked by blue L and blue-dashed line to the north and northeast of Grace). Beyond 72 hours...upper wind forecasts become a lot more favorable for this system as the upper trough is shown to be weakening and lifting northward at that time. Coupled with the somewhat favorable thermodynamic outlook mentioned below...I forecast some brisk development after 72 hours.

Thermodynamic Outlook for the Forecast Period...Through the forecast period the projected path will take this system across very favorable 28 to 29 deg C waters. Moreover...the most recent thermodynamic chart above suggests that the dry saharan air (seen in the bottom-center of the chart) has weakened relative to the timeframe of previous cyclones Fred and Grace. With the dry air being overall weaker...with low vertical shear expected after 72 hrs (which will lessen the chances of dry air getting driven into the circulation)...and with warm waters helping to drive instability for thunderstorms...my current assumption is that dry air won't be as much of a problem for this system as it was for Fred and Grace.

24 Hr Forecast (0000Z Sep 11)...Tropical low centered southeast of the Republic of Cabo Verde at 11N-20.5W

48 Hr Forecast (0000Z Sep 12)...Sheared tropical low centered southwest of the Republic of Cabo Verde at 11.5N-27W

72 Hr Forecast (0000Z Sep 13)...Tropical low centered at 12N-33.5W

96 Hr Forecast (0000Z Sep 14)...40 mph maximum sustained wind tropical storm centered at 12.5N-40W

120 Hr Forecast (0000Z Sep 15)...60 mph maximum sustained wind tropical storm centered at 13N-46.5W

2015 Atlantic Hurricane Season Birdseye Discussion #82A (Special Update)

By: NCHurricane2009, 5:18 AM GMT on September 09, 2015

...WEDNESDAY SEPTEMBER 9 2015 1:20 AM EDT...
Surface low Invest 92-L east-southeast of Bermuda becomes the eighth tropical depression of the 2015 Atlantic Hurricane Season. Visit www.nhc.noaa.gov for up to the minute lastest information on this tropical cyclone. It is very likely that tropical depression eight will strengthen to Tropical Storm Henri later today.

See Invest 92-L special feature section of full discussion #82 for my prognosis and forecast reasoning for newly-formed tropical depression eight. Ignore the statement in the current prognosis about 92-L being subtropical. The National Hurricane Center states that the thunderstorm activity on the east side of the cyclone is strong enough such that the associated latent heat release has generated a vertical warm core just to the east of the parent cold core upper trough such that this system is being designated as tropical depression eight instead of subtropical depression eight. Below I have overlaid my tropical depression eight forecast on top of National Hurricane Center (NHC) 12 AM EDT forecast graphic.

Return to full discussion #82 for an assessment on the rest of the Atlantic tropics...including an update on Tropical Depression Grace.

2015 Atlantic Hurricane Season Birdseye Discussion #82

By: NCHurricane2009, 4:14 AM GMT on September 09, 2015

...WEDNESDAY SEPTEMBER 9 2015 12:15 AM EDT...
Grace as expected weakens to a tropical depression in the central tropical Atlantic while continuing to struggle with dry saharan air and increasing westerly vertical shear and is expected to dissipate into a remnant tropical wave before reaching the Caribbean Sea islands. See special feature section below for an update on Grace. Visit www.nhc.noaa.gov for up-to-the-minute latest information on Grace.

Satellite imagery shows the vigorous tropical wave over Africa has considerably weakened while moving from central to western Africa. Computer models have also stopped showing tropical cyclone formation from this tropical wave when it emerges into the eastern tropical Atlantic in about 2 to 3 days.

Tropical disturbance Invest 92-L east-southeast of Bermuda has become better organized and subtropical or tropical cyclone formation is possible at any time. 92-L is expected to move northward across the northwest Atlantic and toward Newfoundland over the next four days. Interests in the northwest Atlantic should continue to monitor 92-L closely. By the time 92-L reaches Newfoundland it will have transitioned into a non-tropical remnant low...but depending on how strong it gets as a tropical system before the transition it could bring gale force winds to Newfoundland in four days. See Invest 92-L special feature section below for more info on this developing situation.

Over the course of the next week...cool air advection behind the 1003 mb frontal system (seen in top-left of the above atmopsheric features chart below) coming into view from central Canada will deliver a longwave upper trough into the central US...with subsequent shortwave upper troughs diving southeastward on the back side of the longwave. An amplified upper ridge will develop over the western US by the end of the week...potentially causing some of this shortwave energy to evolve into a cut-off upper vortex over Texas. Depending on where exactly the tail end of the surface front ends up in the Gulf of Mexico in relation to the forecast cut-off upper vortex depends on whether or not eastern divergence of cut-off upper vortex triggers a subtropical or tropical disturbance along the front in the western Gulf of Mexico by next week. The usually conservative European (ECMWF) model continues to be the biggest proponent in predicting tropical cyclone formation in this scenario while the GFS no longer shows a cut-off upper vortex forming over Texas and has backed off this scenario. Plenty of time to watch this unfold over the coming days...stay tuned...

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1930Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL DEPRESSION GRACE...
Current Prognosis...Over the past 24 hours Grace continues to struggle while moving into dry saharan air seen to her left in the bottom-center of the above thermodynamics chart. Conditions have become more hostile for Grace as she is moving beneath the south side of an upper trough (marked by blue L and blue-dashed line immediately north of Grace in the above atmopsheric features chart) that is imparting westerly vertical shear across the circulation that is helping to drive the dry air into the circulation. The only thing that has prevented immediate dissipation of Grace is the warm 29 deg C waters supplying enough instability for Grace to fire thunderstorm bursts. As of 0000Z infrared satellite imagery suggested the center of rotation was at 14.5N-46W.

Atmospheric Outlook for the Forecast Period...This system will be steered westward by the 1022 mb Atlantic subtropical ridge through the forecast period. As noted in the above current prognosis...an upper trough is applying unfavorable westerly shear across Grace. Meanwhile...an amplified upper ridge axis (marked by blue-zig-zag line offshore of the southeastern US) has developed in relatively higher upper atmospheric pressures east of the Gulf of Mexico cut-off upper vortex...and additional upper ridging is expected to amplify in the northwest Atlantic due to warm air advection ahead of the 1003 mb frontal system (seen in top-left of the above atmopsheric features chart) coming into the picture from central Canada. All this amplifying upper ridging will push the upper vortex currently southeast of subtropical disturbance Invest 92-L into this storm...continuing the unfavorable shear regime through the remainder of the forecast period.

Thermodynamic Outlook for the Forecast Period...Forecast track keeps this system over very favorable 29 deg C waters. However thermodynamic conditions are becoming less favorable for Grace as she moves into the dry saharan air in the path of the storm (seen in bottom-center of the above thermodynamics chart).


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 10)...Remnant tropical wave with vorticity maximum at approximately 15N-54W

Track Forecast...Tonight's 0000Z fix indicates that Grace is essentially following my previous forecast track...albeit is a bit south of the previous. Therefore my updated forecast track is the same as previous with a slight southward adjustment.

Intensity Forecast...Grace is essentially following my previous intensity forecast while having weakened to a tropical depression. I forecast that in the next 24 hours the negative effects of dry air and shear (mentioned in the above atmo and thermo outlook sections) will cause Grace to degenerate into a remnant tropical wave.

Impact Forecast...No significant impacts are expected as Grace is now below storm force and continues to weaken.

...SPECIAL FEATURE...SURFACE LOW INVEST 92-L...
Current Prognosis...Surface low Invest 92-L east-southeast of Bermuda continues to be supported by upper divergence on the east side of a shortwave upper trough over Bermuda (marked by blue-dashed line immediately left of 92-L in the above atmospheric features chart). Strong thunderstorms have been associated with 92-L all day...but have become biased to the east of the center of 92-L due to westerly shear imparted by the upper trough. As of 0000Z satellite imagery suggested the center of 92-L was pinwheeling stationary while centered at 31N-61.5W. The circulation of 92-L has become better defined...and a recent special update from the National Hurricane Center suggested that a subtropical or tropical cyclone is forming and that advisories declaring the storm could be issued at any time. I think its more likely that 92-L will be initialized as a subtropical cyclone instead of a fully tropical one since this system is primarily being supported by upper divergence on the east side of the cold core upper trough at the moment.

Atmospheric Outlook for the Forecast Period...Surface low Invest 92-L is currently stationary while trapped between two surface ridges marked in the above atmopsheric features chart...one 1022 mb ridge north of the system and a 1018 mb ridge to the southwest of the system. This system is expected to remain stationary for 24 more hours...after which time the 1003 mb frontal system (seen in top-left of the above atmopsheric features chart) coming into view from central Canada moves eastward and knocks out the 1022 mb ridge and pulls 92-L northward. Upper-level winds are expected to become more favorable for 92-L by 48 hrs...when warm air advection ahead of the aforementioned 1003 mb frontal system develops a high-latitude upper ridge south of Atlantic Canada that shifts the parent shortwave upper trough westward and away. Hence I forecast transition of 92-L to a fully tropical storm by 48 hours as the cold core shortwave moves away and as 92-L moves below the very favorable high-latitude warm core upper ridge. By the end of the forecast period...92-L will be merging with the cold front associated with the incoming aforementioned 1003 mb frontal system...transitioning it to non-tropical.

Thermodynamic Outlook for the Forecast Period...This system will be initially stationary over favorable 28 to 29 deg C waters...and then cross the 26 deg C isotherm into cooler waters by 72 hours which will aid in the transition to non-tropical by that time.

24 Hr Forecast (0000Z Sep 10)...50 mph maximum sustained wind subtropical storm centered just east-southeast of Bermuda at 31N-61.5W

48 Hr Forecast (0000Z Sep 11)...50 mph maximum sustained wind tropical storm centered at 35N-61.5W

72 Hr Forecast (0000Z Sep 12)...60 mph maximum sustained wind tropical storm centered at 41N-59W...transitioning to non-tropical

2015 Atlantic Hurricane Season Birdseye Discussion #81

By: NCHurricane2009, 5:52 AM GMT on September 08, 2015

...TUESDAY SEPTEMBER 8 2015 1:52 AM EDT...
Special statement: A lot is going on right now in the Atlantic tropics with six areas of interest. Therefore the following introduction is split into two sections:

...SECTION 1: CONCERNING THE EASTERN HALF OF THE ATLANTIC BASIN...
Tropical Storm Grace in the central tropical Atlantic continues to struggle with dry saharan air and is expected to dissipate into a remnant tropical wave before reaching the Caribbean Sea islands. See special feature section below for an update on Grace. Visit www.nhc.noaa.gov for up-to-the-minute latest information on Grace.

Thunderstorm activity associated with a semi-organized tropical wave emerging from Africa into the eastern tropical Atlantic has continued to decrease. Therefore it is becoming increasingly unlikely that this tropical wave will develop a well-formed circulation prior to reaching the less favorable dry saharan air and wind shear that Grace is currenlty moving into...and therefore tropical cyclone formation from this tropical wave is becoming less likely. Therefore I have cancelled this tropical wave as a special feature on this blog.

A vigorous and already well-organized tropical wave is currenlty moving from interior central to interior western Africa and will be emerging into the eastern tropical Atlantic in about 4 days. Computer models suggest that this tropical wave has potential to develop into a tropical cyclone...and therefore this tropical wave bears watching. Will consider upgrading this tropical wave to a special feature on this blog if it maintains its organization or becomes better organized as it nears the west African coast.

...SECTION 2: CONCERNING THE WESTERN ATLANTIC BASIN AND GULF OF MEXICO...
The 1013 mb surface low in the eastern Gulf of Mexico...supported by upper divergence on the east side of an amplified longwave upper trough over the southeast United States and Gulf of Mexico...has not become better organized but has produced flash flooding thunderstorms across the Florida peninsula. Upper-level winds are becomimg more favorable for tropical development of this surface low as an equally amplified upper ridge develops just east of the longwave upper trough (this upper ridge is marked by a blue-zig-zag line just offshore of the southeastern United States in the atmospheric features chart below). Over the next 24 hours...the 1023 mb surface ridge just offshore of the northeastern US will continue move into the Atlantic....which will cause the currently stationary surface low to move into the southeastern US in southerly steering currents east of the longwave upper trough and west of the surface ridge. With no current signs of tropical development...this surface low is running out of time to tropically develop before it moves ashore and is unlikely to do so.

The old surface trough that was offshore of the Carolinas...mentioned in discussions #73 to #76...indeed has moved across Bermuda and into the waters east of Bermuda as was forecasted during that time. Meanwhile over the past couple of days...upper-level pressures have been rising over eastern Canada and the far northwest Atlantic due to warm air advection ahead of the 1004 mb frontal system (seen in top-left of the atmopsheric features chart below) coming into view from central Canada...triggering a shortwave upper trough/vortex over Bermuda in relatively lower pressures to the south of the rising pressures. In addition...an upper trough/vortex has moved from Puerto Rico/Dominican Republic northeastward to a position southeast of Bermuda. Split flow upper divergence between southwesterlies ahead of the Bermuda upper trough and northwesterlies diving into the back side of the upper vortex southeast of Bermuda have triggered the rapid formation of a surface low east-southeast of Bermuda along the old surface trough. Because this surface low has rapidly developed organized thunderstorms...it has already been classified as tropical disturbance Invest 92-L. 92-L is expected to move northward across the northwest Atlantic and toward Newfoundland over the next five days. Interests in the northwest Atlantic should monitor 92-L closely. By the time 92-L reaches Newfoundland it will have transitioned into a non-tropical remnant low...but depending on how strong it gets as a tropical system before the transition it could bring gale force winds to Newfoundland. See Invest 92-L special feature section below for more info on this developing situation.

Over the course of the next week...cool air advection behind the 1004 mb frontal system (seen in top-left of the atmopsheric features chart below) coming into view from central Canada will deliver a longwave upper trough into the central US...with subsequent shortwave upper troughs diving southeastward on the back side of the longwave. An amplified upper ridge will develop over the western US by the end of the week...causing some of this shortwave energy to evolve into a cut-off upper vortex over Texas. Depending on where exactly the tail end of the surface front ends up in the Gulf of Mexico in relation to the forecast cut-off upper vortex depends on whether or not eastern divergence of the cut-off upper vortex triggers a subtropical or tropical disturbance along the front in the western Gulf of Mexico by next week. The usually conservative European (ECMWF) model has been the biggest proponent in predicting tropical cyclone formation in this scenario...but there is plenty of time to watch this unfold over the coming days...stay tuned...

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1927Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM GRACE...
Current Prognosis...Over the past 24 hours Grace continues to struggle while moving into dry saharan air seen to her left in the bottom-center of the above thermodynamics chart...although recently Grace has fired a storm burst over the center that has prevented her from being downgraded to a tropical depression. As of 0000Z infrared satellite imagery suggested the center of rotation was at 14N-38.5W.

Atmospheric Outlook for the Forecast Period...This system will be steered westward by the 1023 mb Atlantic subtropical ridge through the forecast period. Very soon...Grace will run into unfavorable westerly shear imparted by the shortwave upper trough marked by a blue-dashed line northwest of Grace in the above atmospheric features chart. Meanwhile...an amplified upper ridge axis (marked by blue-zig-zag line offshore of the southeastern US) is developing in relative higher upper atmospheric pressures east of the southeastern US/Gulf of Mexico upper trough...and additional upper ridging is expected to amplify in the northwest Atlantic due to warm air advection ahead of the 1004 mb frontal system (seen in top-left of the above atmopsheric features chart) coming into the picture from central Canada. All this amplifying upper ridging will push the upper vortex currently southeast of Bermuda into this storm...continuing the unfavorable shear regime through 48 hrs and beyond.

Thermodynamic Outlook for the Forecast Period...Forecast track keeps this system over very favorable 29 deg C waters. However thermodynamic conditions are becoming less favorable for Grace as she moves into the dry saharan air in the path of the storm (seen in bottom-center of the above thermodynamics chart)...and thermodynamic conditions will be especially unfavorable farily soon as westerly shear drives this dry air into the circulation.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 9)...30 mph maximum sustained wind tropical depression centered at 15N-46W

48 Hr Forecast (0000Z Sep 10)...Remnant tropical wave with vorticity maximum at approximately 15.5N-54W

Track Forecast...Tonight's 0000Z fix indicates that Grace is essentially following the forecast track presented in special update #80A...albeit is a bit south of that forecast track. Therefore my updated forecast track is the same as in special update #80A with a slight southward adjustment.

Intensity Forecast...Grace is following the updated intensity forecast in special update #80A and therefore I have made no changes since then. Grace will gradually weaken to a remnant tropical wave due to wind shear and dry air mentioned in the above atmopsheric and thermodynamic outlook sections...and I forecast this will occur by 48 hours.

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track.

...SPECIAL FEATURE...SURFACE LOW INVEST 92-L...
Current Prognosis...Satellite imagery over the last 12 hours suggests a surface low has spun up along a surface trough east-southeast of Bermuda...and already features curved storm bands east of the center with clumps of thunderstorms over the surface center. As of 0000Z satellite imagery suggested the system was stationary while centered at 31N-61.5W.

Atmospheric Outlook for the Forecast Period...Surface low Invest 92-L is currently stationary while trapped between two surface ridges marked in the above atmopsheric features chart...one 1023 mb ridge north of the system and a 1018 mb ridge to the south of the system. This system is expected to remain stationary over the next 48 hours...after which time the 1004 mb frontal system (seen in top-left of the above atmopsheric features chart) coming into view from central Canada moves eastward and knocks out the 1023 mb ridge and pulls 92-L northward. Initially 92-L might become sheared and/or suppressed by its parent shortwave upper trough (marked by blue-dashed line to the northwest of 92-L) for the first 48 hrs...after which time warm air advection ahead of the aforementioned 1004 mb frontal system develops a high-latitude upper ridge south of Atlantic Canada that shifts the parent shortwave westward and away. I forecast tropical cyclone formation from 92-L by 72 hours as the shortwave moves away and as 92-L moves below the very favorable high-latitude upper ridge. By the end of the forecast period...92-L will be merging with the cold front associated with the incoming aforementioned 1004 mb frontal system...transitioning it to non-tropical.

Thermodynamic Outlook for the Forecast Period...This system will be initially stationary over favorable 28 to 29 deg C waters...and then cross the 26 deg C isotherm into cooler waters by 96 hours which will aid in the transition to non-tropical by that time.

24 Hr Forecast (0000Z Sep 9)...Surface low centered just east-southeast of Bermuda at 31N-61.5W

48 Hr Forecast (0000Z Sep 10)...Surface low centered just east-southeast of Bermuda at 31N-61.5W

72 Hr Forecast (0000Z Sep 11)...40 mph maximum sustained wind tropical storm centered at 35N-61.5W

96 Hr Forecast (0000Z Sep 12)...50 mph maximum sustained wind tropical storm centered at 40N-60W...transitioning to non-tropical

2015 Atlantic Hurricane Season Birdseye Discussion #80A (Special Update)

By: NCHurricane2009, 5:03 PM GMT on September 07, 2015

...MONDAY SEPTEMBER 7 2015 1:02 PM EDT...
The following special update is to note changes in track and intensity of Tropical Storm Grace moving into the central tropical Atlantic. As of 1500Z...visible satellite imagery showed that the center of Grace already has arrived to 36W longitude. At 1200Z the center was approximately at 35W longitude. Based on the change in positon between 1200Z and 1500Z...I have updated my forecast track to reflect a faster 3-hourly westward motion of 1W longitude. Grace has also begun weakening and so I have also lowered my intensity forecast:

7 Hr Forecast (0000Z Sep 8)...40 mph maximum sustained wind tropical storm centered at 14.2N-38W

31 Hr Forecast (0000Z Sep 9)...30 mph maximum sustained wind tropical depression centered at 15.2N-46W

55 Hr Forecast (0000Z Sep 10)...Remnant tropical wave with vorticity maximum at approximately 15.8N-54W

Return to full discussion #80 for an update on the rest of the Atlantic tropics.

2015 Atlantic Hurricane Season Birdseye Discussion #80

By: NCHurricane2009, 4:31 AM GMT on September 07, 2015

...MONDAY SEPTEMBER 7 2015 12:31 AM EDT...
Even though Fred has been firing strong thunderstorms over the last 24 hours...his circulation has become elongated north-south without a well-defined center and therefore has been downgraded to a broad...elongated remnant low. This elongation may be a sign that Fred is becoming absorbed by the cold front associated with the 1006 mb frontal depression passing by to his north seen in the atmospheric features chart below. Should Fred later seperate from the front and show signs of re-genesis in favorable upper ridging to the south of the front...I will re-upgrade it to a special feature on this blog.

Tropical Storm Grace struggling with dry saharan air ahead of schedule and is more likely to dissipate into a remnant tropical wave before reaching the Caribbean Sea islands. See special feature section below for an update on Grace. Visit www.nhc.noaa.gov for up-to-the-minute latest information on Grace.

Even though its associated thunderstorms have weakened...a tropical wave continues to have signs of organization as it emerges from western Africa and into the eastern tropical Atlantic. See second special feature section below for additional details on this tropical wave. If the forecast in the special feature section holds...the islands of the Republic of Cabo Verde will likely get squally but not severe weather on the north side of this tropical wave in 24 to 48 hours.

The shortwave upper trough energy over the eastern US has consolidated into an amplified longwave upper trough over the southeast United States and Gulf of Mexico. Upper divergence on the east side of the upper trough has triggered the formation of a surface 1015 mb low with well-organized thunderstorms just west of Florida peninsula in the eastern Gulf of Mexico. Upper-level winds could become more favorable for tropical development of this surface low as an equally amplified upper ridge develops just east of the longwave upper trough. Over the next 48 hours...the 1024 mb surface ridge just offshore of the northeastern US will move into the Atlantic....with the surface low likely to move northward into the southeastern US in southerly steering currents east of the longwave upper trough and west of the surface ridge. Currently there are no signs of additional development of this surface low...and none of the computer models forecast this surface low to develop.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1929Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM GRACE...
Current Prognosis...Over the past 24 hours Grace has been struggling to produce thunderstorms while moving into dry saharan air seen to her left in the bottom-center of the above thermodynamics chart. As of 0000Z infrared satellite imagery suggested the center of rotation was at 13.2N-31.8W

Atmospheric Outlook for the Forecast Period...This system will be steered westward by the 1020 mb ridge in the eastern tropical Atlantic early in the forecast period...and later in the forecast period be steered westward by the 1024 mb high-latitude ridge currently moving into the Atlantic from the northeastern US. Later in the forecast period...conditions do not look so good for Grace. After 24 hrs Grace will run into unfavorable westerly shear imparted by the shortwave upper trough marked by a blue-dashed line northwest of Grace in the above atmospheric features chart. Meanwhile...the shortwave upper troughs over the eastern US have consolidated into a single amplified upper trough over the SE US and Gulf of Mexico...which is beginning to create an equally amplified upper ridge in the western Atlantic in relatively higher upper atmospheric pressures east of the upper trough. In turn the amplified western Atlantic upper ridge will push the upper trough currently northeast of the Dominican Republic into this storm...continuing the unfavorable shear regime through 48 hrs and beyond.

Thermodynamic Outlook for the Forecast Period...Forecast track keeps this system over very favorable 29 deg C waters. However thermodynamic conditions are becoming less favorable for Grace as she moves into the dry saharan air in the path of the storm (seen in bottom-center of the above thermodynamics chart)...and thermodynamic conditions will be especially unfavorable after 24 hrs as westerly shear drives this dry air into the circulation.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 8)...50 mph maximum sustained wind tropical storm centered at 14.2N-36.5W

48 Hr Forecast (0000Z Sep 9)...35 mph maximum sustained wind tropical depression centered at 15.2N-40.5W

72 Hr Forecast (0000Z Sep 10)...Remnant tropical wave with vorticity maximum at approximately 15.8N-45.5W

Track Forecast...Tonight's 0000Z fix indicates that Grace is a little south and about 1E longitude of my previous forecast track...and therefore my forecast points for 24 and 48 hrs are adjusted accordingly. My 72 hr forecast point is also a bit south of my previous...but is not 1E of my previous because computer models insist that Grace will travel faster to the west than shown in previous model runs and therefore I prefer to not adjust the 72 hr point by 1E in order to avoid straying too far from the latest model runs.

Intensity Forecast...Grace is now under my previous intensity forecast as dry air has affected her ahead of schedule...and therefore my updated intensity forecast is lower than my previous. Because Grace is still in a low shear environment at the moment...it is possible that the instability provided by the 29 deg C water could allow Grace to fire a storm burst collocated with the center that allows her to maintain current intensity...and this is what I show in my 24 hr intensity forecast. I then forecast Grace to dissipate into a tropical wave by 72 hrs as wind shear drives the dry air into the circulation.

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track.

...SPECIAL FEATURE...TROPICAL WAVE OVER WESTERN AFRICA...
Current Prognosis...Meteosat-9 infrared satellite imagery over last 24 hours suggests that a tropical wave is emerging from Africa and into the eastern tropical Atlantic and is currently located at approximately 17.5W longitude. Thunderstorm activity along the wave axis is weaker compared to 24 hours ago and therefore I have lowered my intensity forecast shown below.

Atmospheric Outlook for the Forecast Period...The tropical wave will be steered westward by the 1020 mb eastern Atlantic ridge...followed by the 1024 mb ridge currently entering the Atlantic from the northeastern United States. The shortwave upper trough marked by a blue-dashed line between Fred and Grace in the above atmospheric features chart has potential to block the northern upper outflow of this tropical wave for the first half of the forecast period...and latest upper-level wind forecasts suggest that the upper trough currenlty northeast of the Dominican Republic will shift eastward and bring some westerly shear along the projected path of this tropical wave later in the forecast period. This is why I show only gradual development of this system in my updated forecast below.

Thermodynamic Outlook for the Forecast Period...This tropical wave will be moving across 29 deg C waters thru the forecast period. However forecast wind shear mentioned in the above atmopspheric outlook section may drive some of the dry saharan air seen in the bottom-center of the above thermodynamics chart into this tropical wave later in the forecast period...another reason why I show only slow development of this tropical wave in the forecast below.

24 Hr Forecast (0000Z Sep 8)...Tropical low pressure centered just southeast of the Republic of Cabo Verde at 12.5N-22.5W

48 Hr Forecast (0000Z Sep 9)...Tropical low pressure centered just southwest of the Republic of Cabo Verde at 13.5N-27.5W

72 Hr Forecast (0000Z Sep 10)...35 mph maximum sustained wind tropical storm centered at 14.5N-32.5W

96 Hr Forecast (0000Z Sep 11)...40 mph maximum sustained wind tropical storm centered at 15.5N-37.5W

120 Hr Forecast (0000Z Sep 12)...45 mph maximum sustained wind tropical storm centered at 16N-42.5W

2015 Atlantic Hurricane Season Birdseye Discussion #79

By: NCHurricane2009, 6:29 AM GMT on September 06, 2015

...SUNDAY SEPTEMBER 6 2015 2:30 AM EDT...
Fred still alive as a tropical depression and expected to meander over the open Atlantic to the southwest of the Azores over the next few days. See special feature section below for an update on Fred. The up-to-the-minute lastest information on Fred can be found at www.nhc.noaa.gov.

Vigorous tropical wave Invest 91-L in the eastern tropical Atlantic intensifies into the seventh tropical storm of the season...and her name is Grace. The new tropical storm is expected to strengthen over the next 48 hours...but will later encounter hostile conditions that will cause it to weaken and perhaps dissipate before reaching the Caribbean Sea islands. See second special feature section below for more information on Grace. The up-to-the-minute lastest information on Grace can be found at www.nhc.noaa.gov.

A tropical wave has become better organized over western Africa tonight and has potential to become yet another tropical cyclone behind Grace over the next five days. See third special feature section below for additional details. If my forecast in the special feature section holds...the islands of the Republic of Cabo Verde will likely get squally but not severe weather on the north side of this tropical wave.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 2156Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL DEPRESSION FRED...
Current Prognosis...Fred weakened to a tropical depression earlier today due to the negative effects of westerly shear on the north side of the tropical Atlantic upper ridge (marked by blue H southwest of Fred in the above atmospheric features chart) and dry saharan air seen to the left of Fred in the above thermodynamics chart getting driven into Fred by the shear. The depression for much of the day had virtually no thunderstorms and displayed itself as a low-level cloud swirl. However as noted in the atmospheric outlook section below...the wind shear is reducing tonight which has very recently allowed Fred to fire a new circular thunderstorm burst directly over the cloud swirl center...therefore Fred is likely to regain tropical storm status in the next 24 hours. As of 0000Z earlier this evening...the surface center of Fred passed over 24N-43W while turning northward.

Atmospheric Outlook for the Forecast Period...The track of Fred is bending increasingly northward while increasingly falling into southerly steering currents on the east side of the 1011 mb surface low located just northeast of Bermuda. Latest computer model runs suggest that this surface low will merge with the tail end of the cold front of the 996 mb frontal cyclone currently located midway between Greenland and Canada. As this 1011 mb surface low merges with the front...it will intensify with the support of upper divergence on the east side of the shortwave upper trough associated with the front and drag Fred eastward while passing to Fred's north. Because models have shifted the track of the 1011 mb low further northward...Fred is now much more likely to get left behind by the surface low at 72 hrs. However the eastward track is likely to continue through 96 and 120 hrs as the 1005 mb frontal depression over SE Montana by that time will be another intense frontal cyclone dragging Fred eastward while passing to Fred's north. After 120 hrs...the track of Fred could reverse westward as the 1025 mb surface ridge currently emerging from the northeastern United States will build to Fred's northwest after the aforementioned 1011 mb surface low and 96 to 120 hr frontal cyclone pass him by. In the upper-levels...wind shear is reducing as some upper ridging is building on top of Fred due to warm air advection ahead of the 996 mb frontal cyclone currently located between Canada and Greenland. Because the 1011 mb surface low and its shortwave upper trough are now expected to be further north than previously thought...and because the 96 to 120 hr frontal cyclone and its upper trough will also pass well to the north...Fred has the potential to remain under favorable upper ridging for much of the forecast period. However by 120 hrs...the back side of the upper trough associated with the 96 to 120 hr frontal cyclone could deliver an upper northwesterly jet that re-increases the shear over Fred while the upper trough amplifies to Fred's northeast.

Thermodynamic Outlook for the Forecast Period...Fred's track will keep him over favorable 27 to 29 deg C waters. Because Fred is expected to turn eastward...he will move away from the unfavorable dry saharan air clearly visible in the bottom-center of the above thermodynamics chart. Therefore thermodynamic parameters are expected to be favorable for the forecast period.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 7)...50 mph maximum sustained wind tropical storm centered at 26.5N-43W

48 Hr Forecast (0000Z Sep 8)...50 mph maximum sustained wind tropical storm centered at 29N-41W

72 Hr Forecast (0000Z Sep 9)...60 mph maximum sustained wind tropical storm centered at 29N-38.5W

96 Hr Forecast (0000Z Sep 10)...60 mph maximum sustained wind tropical storm centered at 29N-35W

120 Hr Forecast (0000Z Sep 11)...50 mph maximum sutained wind tropical storm centered at 29N-33.5W

Track Forecast...My updated track forecast for the first 48 hrs is a 0.2N and 1.5W adjusment from my previous to account for the error between tonight's actual 0000Z fix in the current prognosis and what I previously predicted for 0000Z. Because Fred is no longer expected to get absorbed at 48 hrs...I have extended the forecast track through 120 hrs...following the philosophy of the forecast track shown in discussion #77 which showed an eastward drifting system. The dynamics which will contribute to the eastward track are explained in the above atmospheric outlook section.

Intensity Forecast...Even though Fred is slightly weaker than my previous intensity forecast...my updated forecast is more or less the same or higher than my previous. This is because I am confident Fred should strengthen in the next 24 hours under reduced shear while re-organizing under the current circular storm burst noted in the above current prognosis. I then show gradual strengthening after 24 hrs and through 96 hrs as upper-level wind forecasts have become more favorable due to the fact that the shortwave upper trough associated with the 1011 mb surface low will pass further north than previously thought...leaving Fred to strengthen below favorable upper ridging. The only reason I did not show more rapid strengthening is because upper-level wind forecasts have been changing from day to day and could change again in a way that forecast wind shear could go back up. I then show weakening at 120 hrs in anticipation of forecast northwesterly shear noted at the end of the above atmospheric outlook section.

Impact Forecast...Impact swath in the above graphic assumes that Fred will re-develop into a compact tropical storm.

...SPECIAL FEATURE...TROPICAL STORM GRACE...
Current Prognosis...While taking advantage of warm sea-surface temperatures as well as low shear and enhanced upper outflow beneath an upper ridge...tropical wave Invest 91-L in the eastern tropical Atlantic has strengthened to tropical depression seven and then into Tropical Storm Grace over the past 24 hours. Throughout the day the curved thunderstorm banding became biased to the southwest of the center due to light northeasterly wind shear. This is because the aforementioned upper ridge has become split into two cells (one western cell marked by a blue H in the bottom-center of the above atmpospheric features chart...the other eastern cell marked by a blue-zig zag line in the bottom-right of the chart)...with northeasterly upper winds on the east side of the western cell inducing the light shear. However the most recent satellite frames show the thunderstorm activity becoming more symmetric as Grace moves out of the northeasterly shear while sliding below the western cell. As of 0000Z infrared satellite imagery suggested the center of rotation was at 12.8N-27W and is currenlty on a straight west track on satellite animation.

Atmospheric Outlook for the Forecast Period...This system will be steered westward by the 1020 mb ridge in the eastern tropical Atlantic early in the forecast period...and later in the forecast period be steered westward to west-northwestward by the 1025 mb high-latitude ridge currently moving into the Atlantic from the northeastern US. Later in the forecast period...conditions do not look so good for Grace. As noted in the above current prognosis...the upper ridge that is currently helping Grace has become split into two cells. This is because of a shortwave upper trough (marked by blue-dashed line northwest of Grace) getting pushed southward by upper ridging amplifying over Fred. Grace will run into westerly shear on the south side of the shortwave upper trough at 72 hrs. Then after 72 hrs...the shortwave upper troughs currently over the eastern US will consolidate into a cut-off and amplified upper trough over the SE US...resulting in an equally amplified upper ridge in the western Atlantic in relatively higher upper atmospheric pressures east of the SE US upper trough. In turn the amplified western Atlantic upper ridge will push the upper vortex currently north of the Dominican Republic into this storm...continuing the unfavorable shear regime through 120 hrs and beyond.

Thermodynamic Outlook for the Forecast Period...Forecast track keeps this system over very favorable 29 deg C waters. Even though there is plenty of dry saharan air in the path of the storm (seen in bottom-center of the above thermodynamics chart)...as we are currently seeing with Fred the current expectation is that the instability provided by these warm waters will also allow this system to fire thunderstorms that fight off this dry air. However some of this dry air may get pushed into the circulation by wind shear starting at 72 hrs and beyond.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 7)...60 mph maximum sustained wind tropical storm centered at 13.5N-33W

48 Hr Forecast (0000Z Sep 8)...70 mph maximum sustained wind tropical storm centered at 14.5N-37.5W

72 Hr Forecast (0000Z Sep 9)...60 mph maximum sustained wind tropical storm centered at 15.5N-41.5W

96 Hr Forecast (0000Z Sep 10)...50 mph maximum sustained wind tropical storm centered at 16N-45.5W

120 Hr Forecast (0000Z Sep 11)...35 mph maximum sustained wind tropical depression centered at 16.5N-51W

Track Forecast...Tonight's 0000Z fix indicates that Grace is a little north and 1.5E of my previous forecast track. Therefore my forecast points through 96 hrs are adjusted 1.5E from my previous. Despite the slight northward error...I have not adjusted my track forecast northward because the above current prognosis notes that Grace is moving straight west and will soon catch up with the north-south alignment of the previous forecast track. My new 120 hr forecast point shows a faster west track to catch up to the most recent model runs which have showed Grace moving much faster to the west than previous runs. Therefore additional westward adjustments may be needed in my longer-range forecast track if tonight's model runs turn out to be correct.

Intensity Forecast...Grace has been following my previous intensity forecast perfectly and therefore I have made no changes. After reaching peak strength at 48 hrs...I predict Grace will be weakening to a tropical depression by 120 hrs due to wind shear and dry air noted in the above atmospheric and thermodynamic outlook sections.

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track...with some growth shown due to the expected strengthening of Grace...followed by a dissipation of the swath when I think Grace will weaken below storm force.

...SPECIAL FEATURE...TROPICAL WAVE OVER WESTERN AFRICA...
Current Prognosis...Meteosat-9 infrared satellite imagery over last 24 hours suggests that a tropical wave over interior western Africa has moved from approximately 7.5W longitude to 12.5W longitude. The tropical wave has become increasingly better defined and better organized with strong thundestorms becoming concentrated along the wave axis.

Atmospheric Outlook for the Forecast Period...The tropical wave will be steered westward by the 1020 mb eastern Atlantic ridge thru the forecast period. The shortwave upper trough marked by a blue-dashed line between Fred and Grace in the above atmospheric features chart has potential to block the northern upper outflow of this tropical wave for the first 72 hours which is why I show only gradual development of this tropical wave early in the forecast period. I then show more rapid strengthening of the tropical wave at the end of the forecast period when it reaches a favorable cell of upper ridging that will supply it with low shear and enhanced upper outflow.

Thermodynamic Outlook for the Forecast Period...This tropical wave will be moving into the eastern tropical Atlantic which currently has a moist air mass and 28 to 29 deg C sea surface temperatures favorable for tropical development.

24 Hr Forecast (0000Z Sep 7)...Tropical wave emerging from the west coast of Africa...along 17.5W longitude

48 Hr Forecast (0000Z Sep 8)...Tropical low pressure centered just southeast of the Republic of Cabo Verde at 12.5N-22.5W

72 Hr Forecast (0000Z Sep 9)...35 mph maximum sustained wind tropical depression...centered just southwest of the Republic of Cabo Verde at 13.5N-27.5W

96 Hr Forecast (0000Z Sep 10)...40 mph maximum sustained wind tropical storm centered at 14.5N-32.5W

120 Hr Forecast (0000Z Sep 11)...60 mph maximum sustained wind tropical storm centered at 15.5N-37.5W

2015 Atlantic Hurricane Season Birdseye Discussion #78

By: NCHurricane2009, 6:10 AM GMT on September 05, 2015

...SATURDAY SEPTEMBER 5 2015 2:10 AM EDT...
Tropical Storm Fred continues to hang on and is expected to turn northeastward toward the general direction of the Azores over the next few days. However Fred is more likely to get absorbed by a larger surface low before reaching the Azores. See special feature section below for an update on Fred. The up-to-the-minute lastest information on Fred can be found at www.nhc.noaa.gov.

Vigorous tropical wave Invest 91-L in the eastern tropical Atlantic continues to become better organized and therefore tropical cyclone formation is possible at any time. See second special feature section below for more details.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1935Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM FRED...
Current Prognosis...Fred has been bouncing between tropical depression and minimal tropical storm strength over the last 24 hours...with storm bursts fueled by warm 29 deg C water countering the negative effects of westerly shear on the north side of the tropical Atlantic upper ridge (marked by blue-zig-zag line south of Fred in the above atmospheric features chart) and dry saharan air seen to the left of Fred in the above thermodynamics chart getting driven into Fred by the shear. As of 0000Z earlier this evening...the surface center of Fred passed over 22.8N-39.6W and was seen moving increasingly northward in its westward track in tonight's infrared satellite animation.

Atmospheric Outlook for the Forecast Period...The track of Fred is bending increasingly northward while increasingly falling into southerly steering currents on the east side of the 1010 mb surface low located just northeast of Bermuda. Latest computer model runs suggest that this surface low will merge with the tail end of the cold front of the 1004 mb frontal cyclone currently located midway between Greenland and Canada. As this 1010 mb surface low merges with the front...it will intensify while supported by the shortwave upper trough associated with the front...and therefore this surface low is now expected to last longer and be strong enough to turn Fred northeastward toward the general direction of the Azores. The latest GFS and Euro (ECMWF) models suggest this surface low will become stronger and larger than Fred itself...with Fred becoming absorbed by the surface low before having an opportunity to reach the Azores. This is the solution I am showing in my latest forecast. As far as upper-level winds are concerned...Fred will remain in the westerly shear regime noted in the above current prognosis early in the forecast period...followed by a relaxation in the shear as some upper ridging builds on top of Fred due to warm air advection ahead of the 1004 mb frontal cyclone. Shear is then expected to re-increase at the end of the forecast period due to the passing shortwave upper trough associated with the tail end of the 1004 mb frontal cyclone's cold front.

Thermodynamic Outlook for the Forecast Period...Fred's track will keep him over 28 to 29 deg C waters for much of the forecast period. Despite the presence of adjacent dry saharan air clearly visible in the bottom-center of the above thermodynamics chart...it has become clear that these warm waters are supplying enough instability to allow Fred to fire some strong thunderstorm bursts that are fighting off this dry air...even in the presence of wind shear driving this dry air into the circulation.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 6)...45 mph maximum sustained wind tropical storm centered at 23.8N-41.6W

48 Hr Forecast (0000Z Sep 7)...50 mph maximum sustained wind tropical storm centered at 26.3N-41.6W

72 Hr Forecast (0000Z Sep 8)...35 mph maximum sustained wind tropical depression becoming absorbed...centered at 28.8N-39.6W

Track Forecast...My updated track forecast is a 0.3N and 0.4E adjusment of my previous at all forecast points to account for the error between tonight's actual 0000Z fix in the current prognosis and what I previously predicted for 0000Z.

Intensity Forecast...Fred is following my previous intensity forecast...so my latest intensity forecast is essentially unchanged. I still show some strengthening in the timeframe that is now 24 to 48 hrs away (when a shear-reducing upper ridge builds over Fred as noted in the above atmo outlook section)...followed by showing some weakening by 72 hrs due to shear from a forecast shortwave upper trough (also noted in the above atmo outlook section).

Impact Forecast...Impact swath in the above graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track.

...SPECIAL FEATURE...TROPICAL WAVE INVEST 91-L...
Current Prognosis...Tropical wave Invest 91-L in the eastern tropical Atlantic has continued to organize into a tropical surface low pressure spin with spiral banding showing in its thunderstorm activity...and therefore tropical cyclone formation is possible at any time. As of 0000Z infrared satellite imagery suggested the center of rotation was at 11.5N-22.5W which is slightly east of where I predicted it would be...and therefore I have adjusted all my forecast points to be east of my previous.

Atmospheric Outlook for the Forecast Period...This system will be steered westward by the 1020 mb ridge in the eastern tropical Atlantic early in the forecast period...and later in the forecast period be steered westward to west-northwestward by a high-latitude ridge to build behind the departing 1004 mb frontal cyclone currently located between Canada and Greenland. Upper-level winds are favorable for development with this system currently thriving in low shear and enhanced outflow beneath an upper ridge in the eastern tropical Atlantic (marked by blue H and blue-zig-zag line in the lower-right portion of the above atmospheric features chart). Later in the forecast period...conditions do not look as favorable for this system and therefore I predict weakening by that time. As noted in the atmospheric outlook section for Fred...the 1010 mb surface low northeast of Bermuda is now expected to last longer and become stronger than previously thought...with warm air advection ahead of the surface low amplifying upper ridging in the northeastern Atlantic that will push the shortwave upper trough associated with the 1015 mb central Atlantic surface low southward into this storm. This shortwave upper trough will increase unfavorable vertical shear over this storm by 96 hrs. Then after 96 hrs...the shortwave upper troughs currently over the eastern US will consolidate into a cut-off and amplified upper trough over the SE US...resulting in an equally amplified upper ridge in the western Atlantic in relatively higher upper atmospheric pressures east of the SE US upper trough. In turn the amplified western Atlantic upper ridge will push the upper vortex currently over the Dominican Republic into this storm...continuing the unfavorable shear regime through 120 hrs and beyond.

Thermodynamic Outlook for the Forecast Period...Forecast track keeps this system over very favorable 29 deg C waters. Even though there is plenty of dry saharan air in the path of the storm (seen in bottom-center of the above thermodynamics chart)...as we are currently seeing with Fred the current expectation is that the instability provided by these warm waters will also allow this system to fire thunderstorms that fight off this dry air. However some of this dry air may get pushed into the circulation by wind shear by 96 and 120 hrs.

24 Hr Forecast (0000Z Sep 6)...40 mph maximum sustained wind tropical storm centered at 12.5N-28.5W

48 Hr Forecast (0000Z Sep 7)...60 mph maximum sustained wind tropical storm centered at 13.5N-34.5W

72 Hr Forecast (0000Z Sep 8)...70 mph maximum sustained wind tropical storm centered at 14.5N-39W

96 Hr Forecast (0000Z Sep 9)...60 mph maximum sustained wind tropical storm centered at 15.5N-43W

120 Hr Forecast (0000Z Sep 10)...50 mph maximum sustained wind tropical storm centered at 16N-47W

2015 Atlantic Hurricane Season Birdseye Discussion #77

By: NCHurricane2009, 7:31 AM GMT on September 04, 2015

...FRIDAY SEPTEMBER 4 2015 3:31 AM EDT...
Tropical Storm Fred continues to hang on and is expected to meander in the open ocean to the southwest of the Azores over the next few days. See special feature section below for an update on Fred. The up-to-the-minute lastest information on Fred can be found at www.nhc.noaa.gov.

The tropical wave emerging from the west coast of Africa has quickly become better organized and as a result has been upgraded to tropical disturbance Invest 91-L. It has also gained a higher probability of tropical cyclone formation in the National Hurricane Center tropical weather outlook. See second special feature section below for additional detials on this developing situation.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z and 0137Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM FRED...
Current Prognosis...Fred has maintained minimal tropical storm strength...with storm bursts fueled by warm 28 deg C water countering the negative effects of westerly shear on the north side of the tropical Atalntic upper ridge (marked by blue-zig-zag line south of Fred in the above atmospheric features chart) and dry saharan air seen to the left of Fred in the above thermodynamics chart getting driven into Fred by the shear. As of 0000Z earlier this evening...the surface center of Fred passed over 22N-36W and was seen moving nearly straight to the west in tonight's infrared satellite animation.

Atmospheric Outlook for the Forecast Period...The track of Fred has bent increasingly westward as the 993 mb frontal cyclone in the above atmospheric features chart between Canada and Greenland continues lifting slowly northward...which is allowing the ridge weakness in the north-central Atlantic to continue filling. The 1009 mb surface low passing by Bermuda is expected to cause Fred to turn north while steered by the east side of the surface low. By the middle of the forecast period...the lastest model runs suggest that this surface low will already be weakening. Therefore it is possible Fred could either be dragged northeastward by the tail end of the cold front of the departing 993 mb frontal cyclone or begin to turn more westward on the south side of the high-latitude ridge to build behind the frontal cyclone. Model runs have leaned with the northeastward solution...but then show Fred getting left behind by the tail end of the front by the end of the forecast period while stalling to the south of the high-latitude ridge. This is the solution I am going with in my updated forecast track below. As far as upper-level winds are concerned...Fred will remain in the westerly shear regime noted in the above current prognosis early in the forecast period...followed by a relaxation in the shear as some upper ridging builds on top of Fred due to warm air advection ahead of the 993 mb frontal cyclone. Shear is then expected to re-increase at the end of the forecast period due to a passing shortwave upper trough associated with the tail end of the 993 mb frontal cyclone's cold front.

Thermodynamic Outlook for the Forecast Period...Fred's track will keep him over 28 to 29 deg C waters for much of the forecast period. Despite the presence of adjacent dry saharan air clearly visible in the bottom-center of the above thermodynamics chart...it has become clear that these warm waters are supplying enough instability to allow Fred to fire some strong thunderstorm bursts that are fighting off this dry air...even in the presence of wind shear driving this dry air into the circulation.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 5)...40 mph maximum sustained wind tropical storm centered at 22.5N-40W

48 Hr Forecast (0000Z Sep 6)...45 mph maximum sustained wind tropical storm centered at 23.5N-42W

72 Hr Forecast (0000Z Sep 7)...50 mph maximum sustained wind tropical storm centered at 26N-42W

96 Hr Forecast (0000Z Sep 8)...45 mph maximum sustained wind tropical storm centered at 28.5N-40W

120 Hr Forecast (0000Z Sep 9)...45 mph maximum sustained wind tropical storm centered at 28.5N-37.5W

Track Forecast...According to the 0000Z center fix noted in the above current prognosis...Fred is 0.5N and 0.5E of my previous forecast track. But at the same time...Fred is moving straight west instead of west-northwest and therefore I have not adjusted my 24 hr forecast point northward. However...I have made a 0.5E adjustment in my 24 hr forecast point (and also in all forecast points soon after that) because at the current rate Fred is going westward (measured by the 3-hourly motion between 0000Z and 0300Z) he will continue to be 0.5E of the previous forecast track. My 96 and 120 hr forecast points are adjusted more significantly eastward over my previous due to the models leaning with a northeastward turn at the end of the forecast period...as noted in the above atmospheric outlook section.

Intensity Forecast...I predicted Fred to be a remnant low by now...so he is now above my previous intensity forecast. I no longer show Fred dissipating into a remnant low as conditions from this point forward will improve as westerly shear begins to relax. After showing some re-strengthening at 48 to 72 hrs (when a shear-reducing upper ridge builds over Fred as noted in the above atmo outlook section)...I show some weakening by 96 and 120 hrs due to shear from a forecast shortwave upper trough (also noted in the above atmo outlook section).

Impact Forecast...Impact swath in the above graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track.

...SPECIAL FEATURE...TROPICAL WAVE INVEST 91-L...
Current Prognosis...Satellite imagery suggests a tropical wave with thunderstorm flares and rotation has emerged from the west coast of Africa and into the tropical Atlantic to the southeast of the Republic of Cabo Verde. As of 0000Z Meteosat-9 infrared satellite imagery suggested the center of rotation was at 10.5N-16W which is slightly to the west of where I predicted it would be yesterday. Moroever...the most recent satellite frame at 0600Z suggests the center is already at 18W longitude and therefore my forecast track below is faster to the west than the most recent computer model runs. However I gradually slow the westward speed of the tropical wave thru the forecast period to not stray too far from model predictions. The most recent satellite frame also suggests the thunderstorm activity has become well-organized with banding features beginning to show...and therefore I believe tropical cyclone formation is already possible within the next 24 hours.

Atmospheric Outlook for the Forecast Period...This system will be steered westward by the 1022 mb ridge in the eastern tropical Atlantic early in the forecast period...and later in the forecast period be steered westward to west-northwestward by a high-latitude ridge to build behind the departing 993 mb frontal cyclone currently located between Canada and Greenland. Upper-level winds are favorable for development with this system currently thriving in low shear and enhanced outflow beneath an upper ridge in the eastern tropical Atlantic (marked by blue H and blue-zig-zag line in the lower-right portion of the above atmospheric features chart). Coupled with the favorable thermodynamic picture noted in the thermo outlook section below...I predict strengthening to a hurricane by 96 hours. Just beyond the forecast period...conditions do not look as favorable for this system. Models during this time predict the shortwave upper troughs currently over the eastern US to consolidate into a cut-off and amplified upper trough over the SE US...resulting in an equally amplified upper ridge in the western Atlantic in relatively higher upper atmospheric pressures east of the SE US upper trough. In turn the amplified western Atlantic upper ridge will keep the unfavorable upper vortex currently over Puerto Rico suppressed at low-latitudes and may even push the upper vortex into this storm. Therefore like Danny and Erika earlier this season...this system is likely to struggle as it approaches the Caribbean Sea and/or the western Atlantic beyond the forecast period.

Thermodynamic Outlook for the Forecast Period...Forecast track keeps this system in very favorable 28 to 29 deg C waters. Even though there is plenty of dry saharan air in the path of the storm (seen in bottom-center of the above thermodynamics chart)...as we are currently seeing with Fred the current expectation is that the instability provided by these warm waters will also allow this system to fire thunderstorms that fight off this dry air. Also with this system expected to be in a low shear environment for much of the forecast period...this will lessen the chance that dry air gets pushed into the circulation of this system.

24 Hr Forecast (0000Z Sep 5)...45 mph maximum sustained wind tropical storm centered at 11.5N-24W

48 Hr Forecast (0000Z Sep 6)...60 mph maximum sustained wind tropical storm centered at 12.5N-30W

72 Hr Forecast (0000Z Sep 7)...70 mph maximum sustained wind tropical storm centered at 13.5N-36W

96 Hr Forecast (0000Z Sep 8)...80 mph maximum sustained wind hurricane centered at 14.5N-41W

120 Hr Forecast (0000Z Sep 9)...90 mph maximum sustained wind hurricane centered at 15.5N-46W

2015 Atlantic Hurricane Season Birdseye Discussion #76

By: NCHurricane2009, 4:49 AM GMT on September 03, 2015

...THURSDAY SEPTEMBER 3 2015 12:50 AM EDT...
Tropical Storm Fred hangs on to life in the midst of the tropical Atlantic while tapping into warmer sea-surface temperatures. Therefore Fred could last longer than previously thought...but is still expected to stay away from land areas over the next five days. See special feature section below for an update on Fred. The up-to-the-minute lastest information on Fred can be found at www.nhc.noaa.gov.

A surface trough persists offshore of the Carolinas...which extends into the remnant low of Erika currently located over the Florida/Georgia border. Upper-level winds currently remain a little more favorable for development of this surface trough as a portion its parent shortwave upper trough has retrograded westward and away into the central US (marked by blue-dashed line in the above atmospheric features chart) because of the expanding and favorable upper ridge centered over Florida (marked by blue H). However there are no current signs of tropical development along this surface trough. The parent shortwave upper trough currently over the central US...followed by a parade of shortwave upper troughs to follow behind from the US and eastern Canada...are expected to move offshore and increase unfavorable westerly shear over this surface trough as the surface trough moves across Bermuda and into the waters east of Bermuda over the next 4 days. Computer models are now less favorable for subtropical cyclone formation when this system is east of Bermuda at day 4 as they no longer evolve the shortwave upper trough energy into a shear-reducing cut-off upper vortex. Therefore subtropical cyclone formation is less likely.

Satellite imagery suggests a vigorous tropical wave with thunderstorm flares and rotation over interior western Africa has moved from 5W to 10W longitude over the last 24 hours. This tropical wave has gained intermittent mention over the last couple of days in the National Hurricane Center 5-day tropical weather outlook. At its current forward pace...the tropical wave will be passing directly south of the Republic of Cabo Verde in 72 hours...and be west-southwest of the islands of the Republic at approximately 35-west longitude by 120 hours. Current computer model upper-level wind forecasts indicate that the TUTT (Tropical Upper Tropospheric Trough) fragment that sheared apart Fred should retrograde westward and away from the tropical wave for the first 96 hours which would mean that this tropical wave would have a chance at development. Therefore if these upper-level wind forecasts continue and this tropical wave shows signs of rapid organization as it emerges from Africa in the next 24 hours...I will be upgrading it to a special feature on this blog with a high chance of tropical cyclone formation. On the other hand...if upper-level wind forecasts change in a way that shears this tropical wave...the dry Saharan air layer seen in the bottom-center of the thermodynamics chart below could be driven into this tropical wave before it has a chance to become a well-formed circulation that fires strong storm bursts over warm waters that fight off the dry air (much like what Fred is doing now).

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1927Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM FRED...
Current Prognosis...Fred has weakened further to a minimal tropical storm during the last 24 hours due to westerly shear imparted by a northeastward-moving TUTT (Tropical Upper Tropospheric Trough) fragment currently marked as a blue-dashed line just northwest of Fred in the above atmospheric features chart...and due to dry saharan air seen to the left of Fred in the above thermodynamics chart being driven into the circulation due to the wind shear. But instead of dissipating into a remnant low tonight...Fred's increasingly westward track has allowed him to move into warmer waters that have fueled some intense storm bursts such that he remains a minimal tropical storm tonight. In earlier forecasts I put out in discussions #71 and #72...I predicted that Fred could possibly survive the dry air and shear during the current timeframe by moving into increasingly warm waters...and indeed this is what is occuring now. As of 0000Z earlier this evening...the surface center of Fred passed over 20.5N-32.5W.

Atmospheric Outlook for the Forecast Period...The track of Fred has bent increasingly westward as the 999 mb frontal cyclone in the above atmospheric features chart just offshore of Canada continues lifting slowly northward...which is allowing the ridge weakness in the north-central Atlantic to begin filling. The surface trough currently offshore of the southeastern US is expected to evolve into a surface low east of Bermuda as noted in the above introduction section of tonight's discussion...with Fred expected to turn northward later in the forecast period while steered by the east side of this surface low. By the end of the forecast period...the lastest model runs suggest that this surface low will already be weakening. Therefore it is possible Fred could either be dragged northeastward by the tail end of the cold front of the departing 999 mb frontal cyclone or begin to turn more westward on the south side of the high-latitude ridge to build behind the frontal cyclone. With either scenario possible...I have gone with a neutral northward track through 120 hours for now until it is more clear which way Fred could turn. As far as upper-level winds are concerned...the TUTT fragment mentioned in the above current progonosis is expected to pass directly over Fred over the next 48 hours which could increase the shear further...followed by a relaxation in the westerly shear after Fred moves past the TUTT fragment. The 11 PM EDT NHC advisory suggests Fred could regain strength in the relaxed shear later in the forecast period.

Thermodynamic Outlook for the Forecast Period...Fred is expected to track further west into warmer 28 to 29 deg C waters for the remainder of the forecast period. Despite the presence of adjacent dry saharan air clearly visible in the bottom-center of the above thermodynamics chart...it has become clear that these warm waters are supplying enough instability to allow Fred to fire some strong thunderstorm bursts that are fighting off this dry air...even in the presence of wind shear driving this dry air into the circulation.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 4)...Remnant low centered at 21.5N-36.5W

48 Hr Forecast (0000Z Sep 5)...Remnant low centered at 22.5N-40.5W

72 Hr Forecast (0000Z Sep 6)...35 mph maximum sustained wind tropical depression centered at 23.5N-42.5W

96 Hr Forecast (0000Z Sep 7)...40 mph maximum sustained wind tropical storm centered at 26N-42.5W

120 Hr Forecast (0000Z Sep 8)...45 mph maximum sustained wind tropical storm centered at 28.5N-42.5W

Track Forecast...According to the 0000Z center fix noted in the above current prognosis...Fred is on par with my previous forecast track...and therefore my updated track is a continuation of my previous in terms of direction and forward speed for the first 48 hours...followed by a northward turn from my 48 hour position after 48 hours due to influences noted in the above atmospheric outlook section.

Intensity Forecast...I predicted Fred to be a remnant low by now...so he is now above my previous intensity forecast. Despite the increased instability provided by warmer sea-surface temps (as noted in the above current prognosis and therm outlook sections)...I still think Fred will weaken to a remnant low in the next 24 hours as shear will increase further as the TUTT fragment moves directly over Fred (as noted in the above atmo outlook section). However I subsequently expect the instability to help Fred re-generate into a tropical cyclone by 72 hours and beyond after Fred moves past the TUTT fragment. I keep the re-generation intensity forecast on the conservative side due to uncertainty in the longer-term upper-level wind forecasts which could mean more or less shear...and due to the fact that (as noted in the 11 PM EDT NHC advisory) that none of the computer models re-generate Fred in the relaxed shear environment.

Impact Forecast...Impact swath in the above graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track. I have interrupted the swath for the period I believe Fred will be below storm force.

2015 Atlantic Hurricane Season Birdseye Discussion #75

By: NCHurricane2009, 5:39 AM GMT on September 02, 2015

...WEDNESDAY SEPTEMBER 2 2015 1:40 AM EDT...
Special statement: On Sunday...I graciously learned on Dr. Masters blog that a decision was made at the United Nations in late October of 2013 that the Cape Verde Islands are to be referred to as the Republic of Cabo Verde. Henceforth on this blog I will be referring to the Cape Verde Islands as the Republic of Cabo verde.

Fred weakens as expected while moving away from the Republic of Cabo Verde and is soon expected to weaken to a remnant low. See Fred special feature section below for more details.

A surface trough persists offshore of the Carolinas...which extends into the remnant low of Erika currently located in the northeastern Gulf of Mexico. Upper-level winds have become more favorable for development of this surface trough as a portion its parent shortwave upper trough has retrograded westward and away into the central US (marked by blue-dashed line in the above atmospheric features chart) because of the expanding and favorable western Atlantic upper ridge (marked by blue H). However there are no current signs of tropical development along this surface trough. The parent shortwave upper trough currently over the central US...followed by a parade of shortwave upper troughs to follow behind from the US and eastern Canada...are expected to move offshore and initially increase unfavorable westerly shear over this surface trough as the surface trough moves across Bermuda and into the waters east of Bermuda over the next 5 days. After 5 days the CMC...GFS...and Euro (ECMWF) models agree that shear will then reduce as the shortwave upper trough energy evolves into an overhead cut-off upper vortex. Therefore subtropical cyclone development is possible east of Bermuda by day 5 and beyond.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1929Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM FRED...
Current Prognosis...Fred has been on a general weakening trend over the last 24 hours due to westerly shear imparted by a weakening and adjacent upper vortex (what's left of the upper vortex is marked by the blue-dashed line just south of Fred in the above atmospheric features chart) and dry saharan air layer being pushed into the circulation by the shear. Fred briefly re-organized and stopped weakening this past afternoon and early evening...with the center passing over 19.2N-28.5W as of 0000Z earlier this evening. I think Fred stopped weakening after he moved past the weakening upper vortex...finding upper easterlies on the north side of the upper vortex that matched the forward travel of the storm which reduced the wind shear over the storm. However I think this pause in shear is about to end...as a TUTT (Tropical Upper Tropospheric Trough) fragment marked by a blue-dashed line midway between the Lesser Antilles and Azores in the above atmospheric features chart is moving eastward toward Fred and threatening to apply westerly shear on Fred. In fact the most recent 0300Z satellite image showed the low-level center of Fred de-coupling from his thunderstorm core as the shear begins to re-increase...and Fred should soon resume a weakening trend.

Atmospheric Outlook for the Forecast Period...The track of Fred is bending increasingly westward as the 997 mb frontal cyclone in the above atmospheric features chart just offshore of Canada is beginning to lift northward...which is allowing the ridge weakness in the north-central Atlantic to begin filling. As mentioned in the above current prognosis...a TUTT (Tropical Upper Tropospheric Trough) fragment currently marked by a blue-dashed midway between the Lesser Antilles and Azores is expected to apply unfavorable westerly shear across Fred for the remainder of the forecast period.

Thermodynamic Outlook for the Forecast Period...Fred will stay over favorable waters above 26 deg C thru the forecast period. However thermodynamic parameters are not expected to be favorable for Fred due to the dry saharan air layer (SAL). The above thermodynamics chart now clearly shows that northeasterly winds ahead of Fred...caused by the pressure gradient between Fred's cyclonic circulation and the surrounding environment...have driven a massive slug of SAL southwestward in the environment ahead of Fred. Therefore...expect this unfavorable SAL to get driven into Fred by the westerly shear noted in the above atmospheric outlook section.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 3)...Remnant low centered at 20.7N-32.5W

Track Forecast...According to the 0000Z center fix noted in the above current prognosis...Fred is slightly south and west of my previous forecast track...and therefore my updated forecast track is adjusted accordingly.

Intensity Forecast...Fred is following my previous intensity forecast and therefore I have made no changes tonight. I expect wind shear and dry air (mentioned in the above atmo and thermo outlook sections) to continue to weaken Fred into a remnant low in the next 24 hours.

Impact Forecast...Impact swath in the above graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track.

2015 Atlantic Hurricane Season Birdseye Discussion #74

By: NCHurricane2009, 3:06 AM GMT on September 01, 2015

...MONDAY AUGUST 31 2015 11:06 PM EDT...
Special statement: Yesterday...I graciously learned on Dr. Masters blog that a decision was made at the United Nations in late October of 2013 that the Cape Verde Islands are to be referred to as the Republic of Cabo Verde. Henceforth on this blog I will be referring to the Cape Verde Islands as the Republic of Cabo verde.

Fred becomes the first hurricane in recorded history to strike the Repbulic of Cabo Verde...and is now weakening as he begins to exit the Republic. Continue to visit www.nhc.noaa.gov for up to the minute latest information on Fred...including information on warnings in effect for the Republic of Cabo Verde. See special feature section below for additional details on Fred.

A surface trough persists offshore of the Carolinas. Even though a portion of its parent shortwave upper trough has merged with the upper trough associated with the 996 mb frontal cyclone emerging from eastern Canada...a portion of the parent upper shortwave has been left behind as marked by a blue-dashed line over the eastern United States. Even though the surface trough is now under increasingly favorable upper winds under an expanding western Atlantic upper ridge (marked by blue H between the Carolinas and Bermuda in the atmospheric features chart below)...there are no current signs of tropical development. It should be noted that the only computer model that develops this surface trough as it moves eastward toward Bermuda over the next 120 hours is the usually overly-aggressive CMC model. Currently not buying into long-term development of this surface trough as its parent shortwave upper trough currently over the eastern US...followed by a parade of shortwave upper troughs to follow behind...should move offshore and unfavorably increase westerly shear over this surface trough.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1929Z-released WPC analysis.

Features boxed in green...if any...are mentioned in the National Hurricane Center (NHC) traditional 48-hour outlook and or are considered an "Invest" on the Naval Research Laboratory site of the US Navy at the time the chart was generated. I do not box features in green if they are only included in the NHC's longer term 5-day outlook.

In light blue is upper air analysis, with 200 mb wind barbs calculated by GOES satellite imagery showing the upper-level wind direction. Based on the 200 mb wind barbs, blue-dashed lines are locations of upper troughs, blue-zig-zag lines are locations of upper ridges. Blue Ls are locations of upper lows, blue Hs are locations of upper ridges.

In red is surface analysis, with solid lines indicating locations of surface fronts, dashed lines indicating locations of surface troughs, and zig-zag lines indicating surface ridge axes. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

This chart is generated using GOES water vapor satellite imagery. Brown indicates dry air. White, blue, and purple indicates moist air. An increase in moisture indicates slower air parcel lapse rates with elevation and hence an increase toward instability.

Sea-surface temperatures are overlaid with light blue isotherms. The 26 deg C isotherm is highlighted in red. Waters at and south of the 26 deg C isotherm indicate low-level warmth and hence faster environmental lapse rates with elevation (more instability). Waters north of the 26 deg C isotherm indicate slower environmental lapse rates with elevation (less instability).

...SPECIAL FEATURE...TROPICAL STORM FRED...
Current Prognosis...For the first time Fred looks increasingly ragged and also elongated north to south as it runs into unfavorable westerly vertical shear induced by the cut-off upper vortex located adjacent to Fred (marked by blue-dashed line to the left of Fred in the above atmospheric features chart). Fred has recently been downgraded from a hurricane to a tropical storm. As of 0000Z earlier this evening Fred was centered over the northwestern islands of the Republic of Cabo Verde...at 17.4N-25.0W which is 1 longitude east of my previous forecast track.

Atmospheric Outlook for the Forecast Period...The surface subtropical ridge in the eastern Atlantic has re-organized further north around what is currently the 1025 mb center west of Europe supported by upper convergence on the back side of the eastern Atlantic upper trough (marked by blue-dashed line on the upper right corner of the above atmopsheric features chart). This northward re-location of the surface ridge...coupled with the fact Fred is strong/tall enough to be steered by the adjacent cut-off upper vortex mentioned in the above current prognosis....has caused Fred to continue northwestward. Another factor in allowing Fred to continue northwestward is a developing ridge weakness associated with a strong 996 mb frontal cyclone entering the north-central Atlantic from eastern Canada. It is not until 48 hours that the track of Fred will bend more westward as the weakness fills in when the frontal cyclone lifts out to the north. As expected Fred has begun to run into unfavorable southwesterly vertical shear induced by the aforementioned adjacent cut-off upper vortex. Even though the upper vortex is expected to continue weakening...the TUTT (Tropical Upper Tropospheric Trough) currently marked by a blue-dashed midway between the Lesser Antilles and Azores will move in from the west and maintain the shear.

Thermodynamic Outlook for the Forecast Period...Fred will stay over favorable waters above 26 deg C thru the forecast period. However thermodynamic parameters are not expected to be favorable for Fred due to the dry saharan air layer (SAL). The above thermodynamics chart now clearly shows that northeasterly winds ahead of Fred...caused by the pressure gradient between Fred's cyclonic circulation and the surrounding environment...have driven a massive slug of SAL southwestward in the environment ahead of Fred. Therefore...expect this unfavorable SAL to get driven into Fred by the westerly shear noted in the above atmospheric outlook section.


My (red) track and intensity forecast points in the above graphic:

24 Hr Forecast (0000Z Sep 2)...50 mph maximum sustained wind tropical storm centered at 20N-28W

48 Hr Forecast (0000Z Sep 3)...Remnant low centered at 21.5N-32W

Track Forecast...Only small changes in my forecast track tonight. Fred's northwestward trajectory has caused a 1 degree east longitude error with respect to my previous track (as noted in the above current prognosis). The current northwest angle of the track is expected to continue for 24 more hours which will mean Fred will be 2 degrees east of my previous track by that time...so I have adjusted my 0000Z September 2 forecast point to be 2 east longitude from my previous. Fred is still expected to bend more westward in track in the timeframe that is now 48 hrs away as noted in the above atmospheric outlook section.

Intensity Forecast...Even though I correctly predicted the peak intensity Fred would reach today...Fred has begun weakening at a faster rate due to the beginnings of dry air ingestion and wind shear noted in the above atmo and thermo outlook sections. Therefore I now predict Fred to weaken to a remnant low sooner...in the timeframe that is now only 48 hours away.

Impact Forecast...Impact swath in the above graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track. Fred is starting to exit the Republic of Cabo Verde...and therefore weather conditions will start to improve over the Republic through the overnight.


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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