NCHurricane2009's Blog

2014 Atlantic Hurricane Season Birdseye Discussion #79

By: NCHurricane2009, 6:20 AM GMT on August 31, 2014

...SUNDAY AUGUST 31 2014 2:30 AM EDT...
Tropical wave Invest 99-L remains at risk for additional development while moving across the Yucatan and into the Bay of Campeche over the next 48 hours. See special feature section below for additional details.

The eastern Atlantic tropical wave from Africa that was a special feature in discussions #75 and #76...and a tropical wave in the central tropical Atlantic...are contributing to an elongated 1012 mb low pressure system that apperas to be becoming well organized and consolidating near 10N-38W. I have upgraded this system to a special feature on this blog. See second special feature section below for additional details. Interests in the Lesser Antilles should monitor the progress of this system over the next few days.

Shower and thunderstorm activity of a tropical wave over western Africa has rapidly increased between 1200Z and 1800Z this past afternoon. Waiting to see if this activity persists with this tropical wave before upgrading it to a special feature on this blog.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_30_2014_2245Z_zps4e743531.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_30_2014_2045Z_Thermo_zpsf9cd2845.png
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 99-L...
Current Prognosis...Even though the shower and thunderstorm activity associated with this tropical wave is less concentrated relative to 24 hours ago...a spin appears to be developing along the wave axis and was located at 18N-86W as of 0000Z.

Atmospheric Outlook for the Forecast Period...This system will be in a favorable low shear environment on the south side of Gulf upper ridging during the forecast period (marked by blue-zig-zag line and blue H north of 99-L in the above atmospheric features chart). Because this system will be south of the upper ridge axis...if it does develop it will show limited upper outflow on its north side but plenty of equatorward outflow. Track is expected to be west-northwest curving to the northwest at the very end of the forecast period on the southwest side of subtropical low-level ridging...with the system not expected to curve north while missing the ridge weakenesses associated with the current east-central US upper trough/1006 mb frontal cyclone and western US upper trough/1004 mb frontal cyclone following behind.

Thermodynamic Outlook for the Forecast Period...As the thermodynamics chart above shows...this system will be embedded in a very favorable thermodynamic environment thru the forecast period while tracking over 31 to 32 deg C waters and thru a moist airmass.

24 Hr Forecast (0000Z September 1)...Tropical wave axis producing an organizing tropical low over the southern Yucatan Peninslula near 18.5N-90W.

48 Hr Forecast (0000Z September 2)...Organized tropical low over the central Bay of Campeche centered near 19.5N-94.5W

72 Hr Forecast (0000Z September 3)...40 mph max sustained wind tropical storm centered near 20.5N-98W inland over east-central Mexico

96 Hr Forecast (0000Z September 4)...Remnant low over east-central Mexico centered near 22.5N-99W

...SPECIAL FEATURE...CENTRAL ATLANTIC TROPICAL LOW...
Current Prognosis...A well organized tropical low is located at 10N-38W as of 0000Z and is taking advantage of low shear/enhanced outflow below tropical upper ridging (marked by a blue-zig-zag line in the lower right of the above atmospheric features chart). Satellite animation between 1800Z and 0000Z suggests that this tropical low has moved from 35w to 38W...or at a rate of about 3W in 6 hours which is approximately 10 to 12W in 24 hours upon which the early portion of the forecast track below is based on.

Atmospheric Outlook for the Forecast Period...The 1028 mb Atlatnic subtropical ridge which is pushing this system westward is expected to weaken thru the forecast period as the southern portion of the upper trough associated with non-tropical Cristobal merges with what is now a northern fracture of the central US upper trough which is currently over eastern Canada...with the merged cut-off upper trough supporting an impressive surface low that weakens the ridge and obliterates the eastern part of the ridge. The weakening of the ridge will cause the westward speed of the track to slow as this system enters the Caribbean as reflected in the forecast track below. The forecast below also suggests the track bending more northward as this system is predicted to be strong/tall enough to be tugged by the east side of what is now the upper vortex near the Bahamas marked by a blue L/blue-dashed line in the above atmo chart (this upper vortex is expected to last and be generally stationary thru the forecat period). In addition...this upper vortex is likely to impart some westerly shear on this system at the end of the forecast period which is why the forecast intensification rate is flattened during that time.

Thermodynamic Outlook for the Forecast Period...This system is currently over favorable 28 deg C...and will track toward even more favorable waters of 29 to 30 deg C by the end of the forecast period. The above thermo chart shows that the dry Saharan air layer is weaker than ever before during this hurricane season...which is also a favorable factor for this system.

24 Hr Forecast (0000Z September 1)...Organized tropical low centered near 10N-48W

48 Hr Forecast (0000Z September 2)...40 mph max sustained wind tropical storm centered near 11N-58W approaching the southern Lesser Antilles

72 Hr Forecast (0000Z September 3)...60 mph max sustained wind tropical storm centered near 12N-65.5W in the eastern Caribbean Sea

96 Hr Forecast (0000Z September 4)...70 mph max sustained wind tropical storm centered near 14.5N-70.5W in the central Caribbean Sea under light westerly shear

120 Hr Forecast (0000Z September 5)...75 mph max sustained wind hurricane centered near 17N-75.5W just southeast of Jamaica

2014 Atlantic Hurricane Season Birdseye Discussion #78

By: NCHurricane2009, 6:14 AM GMT on August 30, 2014

...SATURDAY AUGUST 30 2014 2:15 AM EDT...
Hurricane Cristobal has transitioned into a severe non-tropical gale moving northeastward across the north Atlantic.

Tropical wave Invest 97-L has become a little better organized while moving into the central Caribbean waters southwest of Jamaica. This system has been re-introduced onto the Naval Reseach Laboratory (NRL) site of the US Navy as Invest 99-L...and is at risk of additional development while moving across the western Caribbean...Yucatan Peninsula...and Bay of Campeche. See special feature section below for additional details.

Surface troughing in the Gulf of Mexico...marked as a red dashed line in the atmoshperhic features chart below...has moved northward into the US Gulf coast while steered between the 1023 mb ridge over eastern North America and 1008 mb frontal cyclone moving across the central US. Although this system developed a little further with an increase in showers and thunderstorms supported by the low shear and outflow of a Gulf of Mexico upper ridge (marked by blue zig zag line)...additional development of this system is no longer possible as it interacts with land.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_29_2014_2245Z_zpsbb9a41ed.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_29_2014_2245Z_Thermo_zps454e7cc1.png
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 99-L (FORMERLY INVEST 97-L)...
Current Prognosis...Tropical wave Invest 99-L is located along 80W longitude this past afternoon and into this evening...becoming a little better organized while the associated showers and thunderstorms is becoming concentrated southwest of Jamaica and northeast of Central America. Satellite animation suggests the vorticity maximum of this tropical wave is along 15N latitude. My updated forecast below is adjusted a bit southward as the location of the vorticity maximum suggests this system is consolidating at a location more southward than I previously expected.

Atmospheric Outlook for the Forecast Period...This system is arriving into a favorable low shear environment to the west of an upper vortex (marked by blue L to the north of 99-L in the above atmo chart) and on the south side of the Gulf upper ridging (marked by blue-zig-zag line). Because this system will be south of the Gulf upper ridge axis during the forecast period...if it does develop it will show limited upper outflow on its north side but plenty of equatorward outflow. Track is expected to be west to west-northwest on the southwest side of subtropical low-level ridging thru the forecast period...with the system not expected to curve north while missing the ridge weakenesses associated with the current central US upper trough/1008 mb frontal cyclone and the next upper trough/surface frontal cyclone (not yet in the atmospheric features chart) to follow behind the 1008 mb frontal cyclone.

Thermodynamic Outlook for the Forecast Period...As the thermodynamics chart above shows...this system will be embedded in a very favorable thermodynamic environment thru the forecast period while tracking over 30 to 31 deg C waters and thru a moist airmass.

24 Hr Forecast (0000Z August 31)...Tropical wave axis in the western Caribbean near 85W longitude producing an organizing storm cluster southwest of the Cayman Islands

48 Hr Forecast (0000Z September 1)...Tropical wave axis producing an organizing tropical low over the southern Yucatan Peninslula near 18N-89W.

72 Hr Forecast (0000Z September 2)...Organized tropical low over the eastern Bay of Campeche centered near 19N-93.5W

96 Hr Forecast (0000Z September 3)...45 mph max sustained wind tropical storm centered near 20N-97W making landfall in east-central Mexico

120 Hr Forecast (0000Z September 4)...Remnant low over east-central Mexico centered near 21.5N-98.5W

2014 Atlantic Hurricane Season Birdseye Discussion #77

By: NCHurricane2009, 9:09 AM GMT on August 29, 2014

...FRIDAY AUGUST 29 2014 5:10 AM EDT...
Hurricane Cristobal rapidly accelerating northeastward across the northern Atlantic while transitioning into a large and dangerous non-tropical cyclone for shipping lanes. See special feature section below for additional details on Cristobal. Visit www.nhc.noaa.gov for up-to-the-minute the latest information on this system...including watches/warnings.

Computer model support showing tropical wave Invest 97-L developing in the western Caribbean...Yucatan...and then Bay of Campeche by 96 to 120 hours has increased. In addition this tropical wave has become sufficiently organized south of Haiti and the Dominican Republic this early morning for an upgrade to a special feature ont this blog. See second special feature section below for additional details on this system.

The vigorous tropical wave that has emerged from western Africa and into the eastern tropical Atlantic has suddenly seen a loss in showers and thunderstorms over the last 24 hours. Computer model support for this system has also decreased considerably. Their is potential for this tropical wave to encounter unfavorable westerly shear from a tropical upper tropospheric trough (TUTT) as it moves into the central tropical Atlantic by 96 hours (this TUTT is marked bya series of blue dashed lines to the northwest of the tropical wave in the atmoshperic features chart below). Even if the tropical wave stays south of the TUTT and in favorable upper winds below the tropical upper ridge (marked by blue-zig-zag lines in the lower-right of the atmoshperhic featuers chart)...its lack of development means it is now less likely to have a robust moisture field by the time it encounters the dry Saharan air layer in the central tropical Atlantic. I have cancelled this tropical wave as a special feature on this blog.

Surface troughing in the Gulf of Mexico...marked as a red dashed line in the atmoshperhic features chart below...persists in the Gulf of Mexico. Surface low Invest 98-L has broken from the surface trough and has moved westward and made landfall in the Texas/Mexico border without developing as expected. Meanwhile back over the Gulf of Mexico...another surface low located in the western Gulf appears to be developing on the surface trough due to upper divergence on the southeast side of the small upper trough from Texas (marked by blue dashed line) which has moved eastward into Louisiana. Upper ridging over the Gulf (marked by blue zig zag line) is also providing outflow supporting this surface low. Westerly shear from the Louisana upper trough should decrease while it shifts north and become absorbed into the western US upper trough. And with the moisture content increased across the Gulf relative to yesterday...coupled with favorable low shear and outflow from the Gulf upper ridge...their is potential for short-term development with this new surface low. A west-northwest to northwest track in the short-term would be expected between the 1021 mb ridge over eastern North America and 1008 mb frontal cyclone supported by the western US upper trough...followed by a west-northwest to northwest track due to a ridge weakness from the next upper trough/surface frontal cyclone (not yet in the atmospheric features chart) to follow behind the 1008 mb frontal cyclone.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_29_2014_0015Z_zpsa50468cb.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z and the 0127Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_29_2014_0015Z_Thermo_zpseed798b6.png
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...HURRICANE CRISTOBAL...
Current prognosis...As of the 11 PM EDT National Hurricane Center advisory...the center of Hurricane Cristobal was located in the northwestern ATlantic at 40.2N-56.6W and was moving extremly fast to the east-northeast at 46 mph. Because the hurricane is moving rapidly..it has matched the speed of the upper westerly winds associated with the shortwave upper trough it is interacting with (shortwave upper trough marked as blue-dashed line northwest of Cristobal in the atmospheric featuers chart above). Therefore the westerly shear from the upper winds has been minimal...which allowed Cristobal to strengthen to 85 mph maximum sustianed with a pressure drop to 970 mb due to sea surface temps above 26 deg C and upper divergence on the east side of the shortwave upper trough. These are the highest winds and lowest pressure the storm has ever exhibited in its lifespan.

Atmospheric Outlook for the Forecast Period...Cristobal's east-northeast track is a result of it being embedded in deep-layered westerly flow south of the surface cold front trailing from the north Atlantic 974 mb frontal cyclone...and south of the shortwave upper trough associated with the frontal cyclone (this shortwave upper trough was referenced in the above current prognosis section). Cristobal is expected to soon transition into a large and strong non-tropical system supported by divergence on the southeast side of the shortwave upper trough...with the track expected to remain fast and bend increasingly north when the back side of Cristobal's circulation pulls down the cooler air associated with the shortwave upper trough which makes the upper trough stronger/more amplified.

Thermodynamic Outlook for the Forecast Period...Cristobal has just crossed the 26 deg C isotherm into cooler waters...which is causing the thunderstorms to weaken such that Cristobal will lose its warm core (supported by the latent heat release of the thunderstorms) and transition into a non-tropical cyclone as outlined in the above atmospheric outlook seciton. Thermodynamic parameters such as sea-surface temps and dry air will soon be irrelevant as a non-tropical Cristobal maintains its strength from divergence on the southeast side of the shortwave upper trough.

 photo Aug_29_2014_H_Cristobal_Forecast_zps952d797c.png

Track Forecast...After initially staying a bit left of the NHC forecast track last night...Cristobal all day yesterday and thru this morning took a hard right turn and is now a bit right of the previous track guidance from 24 hours ago. Therefore the NHC track has been adjusted to the right relative to yesterday...and I see no reason to disagree with the NHC forecast track with computer models in strong agreement with that track.

Intensity Forecast...Even though this hurricane is headed to cooler waters...the weakening rate is forecast to be only gradual as it transitions into a non-tropical frontal cyclone supported by upper atmospheric dynamics as discussed in the above atmospheric outlook section. Because Cristobal is stronger than I thought it would be...my updated intensity forecast above is bumped up from the previous and is now in agreement with the latest intensity forecast from the 11 PM EDT NHC advisory.

Impact Forecast...The above-illustrated impact swath...which is an extrapolation of the 11 PM EDT NHC tropical storm wind field along the forecast track...suggests that no land areas are forecast to received sustained winds of tropical storm force due to the forecast track. Large sea swells and rip currents will also be another effect of this storm as noted in impact statement (c) in the above forecast graphic.

...SPECIAL FEATURE...TROPICAL WAVE INVEST 97-L...
Current Prognosis...Tropical wave Invest 97-L has recently become better organized this early morning while producing a circular cluster of showers and thunderstorms in the Caribbean Sea at a location just south of Haiti and the Dominican Republic. This system continues to take advantage of upper anticyclonic flow that is low in shear and producing outflow at the west end of tropical upper ridging (currently marked by blue zig-zag lines in the above atmospheric featuers chart). This upper anticyclonic flow is located in relative higher upper atmospheric pressures to the south of an upper vortex (marked by blue L) and to the east of an inverted upper trough (marked by blue dashed line left of 97-L).

Atmospheric Outlook for the Forecast Period...The upper vortex to the north is expected to retrograde westward around the Gulf upper ridge and eastern North America upper ridge marked by blue zig-zag lines in the above atmospheric features chart. The inverted upper trough to the west is also expected to retrograde westward while weakening. Therefore early in the forecast period... this tropical wave will remain coupled with the favorable upper anticyclonic flow also to shift west in between the upper vortex and inverted upper trough. However the forecast below shows light westerly shear as the southwestern lobe of the upper vortex may get pushed a bit southward into the environment of this tropical wave due to the strength of the eastern North America/Gulf of Mexico upper ridging. By the end of the forecast period...this system will have arrived into a favorable low shear environment to the west of the upper vortex and on the south side of the Gulf upper ridging. Because this system will be south of the Gulf upper ridge axis during the forecast period...if it does develop it will show limited upper outflow on its north side but plenty of equatorward outflow. Track is expected to be west to west-northwest on the southwest side of subtropical low-level ridging thru the forecast period...with the system not expected to curve north while missing the ridge weakenesses associated with the current western US upper trough/1008 mb frontal cyclone and the next upper trough/surface frontal cyclone (not yet in the atmospheric features chart) to follow behind the 1008 mb frontal cyclone.

Thermodynamic Outlook for the Forecast Period...As the thermodynamics chart above shows...this system is now moving westward while leaving behind the dry Saharan air layer to the northeast and moving into very favorable thermodynamic parameters...including a rather moist airmass across the Caribbean and Gulf of Mexico...and sea surface temps in the 29 to 31 deg C range.

24 Hr Forecast (0000Z August 30)...Tropical wave axis in the central Caribbean near 79W longitude producing a semi-organized storm cluster over and southwest of Jamaica. Semi-organized storm cluster under light westerly shear.

48 Hr Forecast (0000Z August 31)...Tropical wave axis in the western Caribbean near 84W longitude producing an organizing storm cluster west-southwest of the Cayman Islands

72 Hr Forecast (0000Z September 1)...Tropical wave axis producing an organizing tropical low over the Yucatan Peninslula near 20N-88W.

96 Hr Forecast (0000Z September 2)...Organized tropical low over the eastern Bay of Campeche centered near 21N-92.5W

120 Hr Forecast (0000Z September 3)...45 mph max sustained wind tropical storm centered near 22N-96W approaching east-central Mexico

2014 Atlantic Hurricane Season Birdseye Discussion #76

By: NCHurricane2009, 6:51 AM GMT on August 28, 2014

...THURSDAY AUGUST 28 2014 2:52 AM EDT...
Hurricane Cristobal to rapidly accelerate northeastward across the northwestern and northern Atlantic over the next few days while transitioning into a large and vigorous non-tropical cyclone. See special feature section below for additional details on Cristobal. Visit www.nhc.noaa.gov for up-to-the-minute the latest information on this system...including watches/warnings.

Tropical wave Invest 97-L currently crossing the Lesser Antilles and moving into the Caribbean Sea has seen an increase in thunderstorms while taking advantage of reduced shear and enhanced outflow below an expanding upper anticyclone at the west end of tropical upper ridging (currently marked by blue H in the atmospheric features chart below). This upper anticyclone is located south of a tropical upper tropospheric trough (TUTT) and east of an inverted upper trough...both marked by blue dashed lines. An upper vortex is forecast to fracture off the western end of the TUTT and retorgrade westward...and the inverted upper trough is also expected to retrograde westward and weaken...and therefore this tropical wave has the potential to be coupled with the favorable upper anticyclone also to shift west in between the upper vortex and inverted upper trough. Therefore some gradual development of this tropical wave is possible as it tracks across the Caribbean in the next 96 hours. Between 96 and 120 hours as this tropical wave shifts from the western Caribbean to the Bay of Campeche...conditions could become less favorable for development due to land interaction with the Yucatan peninsula and a burst of westerly shear as the southwestern lobe of the upper vortex shifts southward. Then by 144 hours (6 days)...the tropical wave has the potential to re-enter favorable conditions in the Bay of Campeche to the west of the upper vortex. Perhaps this explains some of the computer model runs that developed this system in the Bay of Campeche referenced in the intro section of discussion #74. Not upgrading this system to a special feature on this blog unless this system shows additional signs of organization.

The vigorous tropical wave with widespread showers and thunderstorms from western Africa remains organized as it enters the eastern tropical Atlantic...see the second special feature section below for additional details.

Off the coast of Texas...the Gulf of Mexico surface trough developed a cloud swirl surface low pressure spin that was upgraded to Invest 98-L and investigated by recon aircraft this past afternoon when it breifly developed an increase in showers and thunderstorms. This system remains between a Gulf of Mexico upper anticyclone (marked as a blue H to the southeast of 98-L in the atmospherhic features chart below) and an inverted upper trough that has moved northward into Texas around the anticyclone (marked as a blue dashed line to the northwest of 98-L). While the cloud swirl surface low continues to be supported by upper divergence between the inverted upper trough and Gulf upper anticyclone...the re-positioning of the upper trough to a location now northwest of the disturbance places the disturbance under less favorable shearing upper westerly winds on the southeast side of the upper trough. In addition dry air continues to prevent development of this system (see the paragraph on the Gulf of Mexico surface trough in the intro section of discussion #75 for the sources of this dry air).

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_27_2014_2045Z_zps7c25962e.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_27_2014_2045Z_Thermo_zps01fb439e.png
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...HURRICANE CRISTOBAL...
Current prognosis...As of the 2 AM EDT National Hurricane Center advisory...the center of Hurricane Cristobal was located at 34.6N-69.0W..midway between the North Carolina coast and Bermuda and turning and accelerating to the northeast. After weakening early yesterday morning due to dry air ingestion and due to a suppressing shallow upper vortex overhead...Cristobal this past afternoon thru early this morning has recovered as the shallow upper vortex has weakened to a skinny north-south upper trough just west of the hurricane...marked as a blue dashed line just to the left of Cristobal in the above atmospheric features chart. Despite the revival of a core of thunderstorms over the center...Cristobal has not re-strengthened.

Atmospheric Outlook for the Forecast Period...Cristobal is turning and accelerating northeastward in deep-layered westerly flow south of the surface cold front trailing from the 985 mb frontal cyclone that has recently entered the far north Atlantic from eastern Canada...and south of this frontal cyclone's vigorous upper trough. The upper trough consists of two shortwaves...one just west of the 985 mb center of the frontal cyclone...the second over southeastern Canada...both marked by blue-dashed lines in the above atmo chart. By the end of the forecast period...Cristobal is expected to transition into a large and strong non-tropical system supported by divergence on the southeast side of the western of the two aformentioned shortwave upper troughs....with the track expected to be rather fast and bend increasingly north when the back side of Cristobal's circulation pulls down the cooler air associated with the shortwave upper trough which makes the upper trough stronger/more amplified.

Thermodynamic Outlook for the Forecast Period...Cristobal remains over 28 to 29 deg C waters...and on the forecast track shown below this storm will cross the 26 deg C isotherm into cooler waters by late today. However the decreasing sea-surface temps will no longer be relevant to Cristobal's strength as it transitions into a non-tropical system supported by upper atmospheric dynamics by Friday. Dry air persists west of Cristobal due to upper convergence on the west side of the skinny north-south upper trough mentioned in the above current prognosis section...but Cristobal seems to be unaffected by this dry air while maintaining a core of thunderstorms this evening and while it begins to accelerate northeastward and away from this dry air.

 photo Aug_27_2014_H_Cristobal_Forecast_zps72c85f71.png

Track Forecast...My updated forecast track above is adjusted a bit southward from my previous as Cristobal's recent positions this evening and this early morning are a bit south of the previous. However I remain a bit left of the latest NHC forecast track as satellite animation suggests Cristobal is not turning as sharply to the right to stay on course with the lastest NHC track.

Intensity Forecast...Even though this hurricane is headed to cooler waters and westerly shear...the weakening rate is forecast to be only gradual as it transitions into a non-tropical frontal cyclone supported by upper atmospheric dynamics as discussed in the above atmospheric outlook section. My updated intensity forecast above is the same as previous as the previous intensity forecast has so far been 100% accurate.

Impact Forecast...The above-illustrated impact swath...which is an extrapolation of the 11 PM EDT NHC tropical storm wind field along my forecast track...suggests that no land areas are forecast to received sustained winds of tropical storm force due to the forecast track...but their is a suggestion of a close call for Bermuda in the next few hours and another close call for southeastern Newfoundland for Friday morning. Regardless...Bermuda and southeastern Newfoundland will be too far from the center to get any significant wind impacts. Surf and rip currents will also be another effect of this storm as noted in impact statement (c) in the above forecast graphic.

...SPECIAL FEATURE...STRONG TROPICAL WAVE EMERGING FROM WESTERN AFRICA...
Current Prognosis...Based on the lastest Meteosat-9 satellite imagery...the tropical wave axis is estimated to be at 17.5W longitude as it leaves western Africa and enters the eastern tropical Atlantic. The organization of the thunderstorms suggests the vorticity maximum of the tropical wave is located along 12N latitude...further north than the previous estimate of 8N made in dsicussion #75...and therefore my updated forecast track below is a northward shift from my previous. I have also delayed the timeframe of forecast tropical cyclone formation as this system has not become better organized relative to yesterday.

Atmospheric Outlook for the Forecast Period...The tropical wave is expected to take advantage of favorable tropical upper ridging (currently marked by blue-zig-zag in the lower-right in the atmo chart above). A central Atlantic upper ridge will be doubly enforced by warm air advection ahead of what is expected to be a large/vigorous non-tropical Cristobal thru the forecast period. A consequence of the central Atlantic upper ridge is that a tropical upper tropospheric trough (TUTT) is re-enforced in relatively lower pressures between the central Atlantic upper ridge and aforementioned tropical upper ridge. This system is expected to stay southeast of the unfavorable TUTT thru the forecast period until the very end of the forecast...when this system is expected to begin to dealing with westerly shear imparted by the TUTT.

Thermodynamic Outlook for the Forecast Period...This system is entering 28 to 29 deg C waters in the eastern tropical Atlantic...will decrease to a minimum of 27 to 28 deg C in the middle of the forecast period...afterwards increasing to above 28 deg C at the end of the forecast period if this system follows the forecast track below. These water temps are favorable for development. The northward shift in the forecast track below makes it more likely to track into and be affected by the dry Saharan air at the end of the forecast period.

24 Hr Forecast (0000Z August 29)...Tropical low located near 13N-25W...or just south of the Cape Verde Islands

48 Hr Forecast (0000Z August 30)...Organized tropical low located near 14.5N-31W...or southwest of the Cape Verde Islands

72 Hr Forecast (0000Z August 31)...35 mph max sustained wind tropical depression centered near 15.5N-36W

96 Hr Forecast (0000Z September 1)...45 mph max sustained wind troipcal storm centered near 17N-41W

120 Hr Forecast (0000Z September 2)...60 mph max sustained wind tropical storm under westerly shear centered near 18N-46W

2014 Atlantic Hurricane Season Birdseye Discussion #75

By: NCHurricane2009, 7:47 AM GMT on August 27, 2014

...WEDNESDAY AUGUST 27 2014 3:45 AM EDT...
Cristobal to rapidly accelerate northeastward across the western and northern Atlantic over the next few days...at first as a large and vigorous tropical cyclone transitioning into a large and vigorous non-tropical cyclone. The forecast track guidance is has shifted west over the last 24 hours such that the threat to Bermuda is reduced and the threat to southeastern Newfoundland has increased. See special feature section below for additional details on Cristobal. Visit www.nhc.noaa.gov for up-to-the-minute the latest information on this system...including watches/warnings.

Tropical wave Invest 97-L currently east of the Lesser Antilles previously received attention from the NRL and NHC because conditions were expected to be generally more favorable for development as the dry Saharan air layer is weaker relative to earlier this month and with the expectation this system would take advantage of favorable tropical upper ridging (currently marked by blue-zig-zag in the lower-right in the atmo chart below). Instead this system continues to struggle with the dry Saharan air layer to its north. Moreover a central Atlantic upper ridge has been forming due to the latent heat release of Hurricane Cristobal and due to warm air advection ahead of a series of frontal cyclones supported by the western Atlantic upper trough. A tropical upper tropospheric trough (TUTT) has been forming between the central Atlantic upper ridge and aforementioned tropical upper ridge...with this system also battling unfavorable westerly shear on the south side of the TUTT. This system will likely continue dealing with unfavorable shear while following an upper vortex forecast to fracture off the western end of the TUTT. Furthermore with computer model support dropping for this system...development of 97-L is not expected.

The vigorous tropical wave with widespread showers and thunderstorms over western Africa remains organized as it nears the west African coast...and computer model support suggesting quick development as it enters the Atlantic tropics is increasing. Therefore this tropical wave has been upgraded to a special feature on this blog. See the second special feature section below for additional details.

The western Atlantic upper trough that Hurricane Cristobal is currently interacting with previously supported a lengthy surface front...the tail end of which has decayed into a surface trough over the Gulf of Mexico as marked by an east-west red-dashed line in the atmospheric features chart below. In the atmospheric outlook of Cristobal written during discussion #73...their was a southeastern Gulf of Mexico inverted upper trough retrograding westward around the eastern US upper ridge..and this inverted upper trough (marked as a blue-dashed line) is currently over southern Texas/northern Mexico. In addition...the vast upper anticyclone over Cristobal when it was a young storm has been split by the western Atlantic upper trough...with the western split evolving into a Gulf anticyclone as marked by a blue H. Split flow upper divergence between the norheast side of the inverted upper trough and Gulf upper anticyclone has been supporting intermittent bursts of disturbed weather over and offshore of Texas/Louisana and along the surface trough. However as outlined in the thermodynamic outlook of Cristobal written during discussion #73...this region was and still is dry as some dry air had collected below the inverted upper trough (and this dry air is still over the southern Gulf) and as dry air persits on the western convergent side of the western Atlantic upper trough. With the dry air and lack of computer model support...development is not expected along the Gulf surface trough.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_26_2014_2045Z_zps76abb55a.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_26_2014_2045Z_Thermo_zps0fc21f05.png
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...HURRICANE CRISTOBAL...
Current prognosis...As of the 11 PM EDT National Hurricane Center advisory...the center of Hurricane Cristobal was located at 30.4N-71.5W...indicating Cristobal has tracked further to the left and a little faster than previous track guidance from 24 hours ago. My previous expectation during discussion #74 was Cristobal would lean a little more to the right in its northward track while consolidating below a strong storm canopy and associated small upper anticyclone that I was forecasting to form just southeast of the western Atlantic upper trough. Instead Cristobal and its strong thunderstorms have moved straight north directly into the upper trough...with the latent heat release of these storms punching out the upper trough such that it has weakened into two upper vortices as marked by a pair of blue Ls (one directly over Cristobal and another northeast of Cristobal). Remarkably Cristobal this past afternoon was able to maintain a ball of central thunderstorms while sliding below the southern upper vortex...perhaps suggesting the upper vortex was becoming so shallow that it was an aid to Cristobal instead of a suppressor. For instance shear has been reduced by the shallow upper vortex as its cyclonic flow matches the surface cyclonic flow of the storm...and widespread upper divergence between the north side of the upper vortex and west side of the upper ridge axis (marked by blue-zig-zag line to the southeast) has aided in widespread surface pressure falls supporting the additional strengthening and expansion of the wind field observed by aircraft reconnaissance. In recent hours since the 11 PM EDT NHC advisory...Cristobal has finally gained a more typical apperance of a tropical cyclone located below an upper vortex with the thunderstorms weakening and taking a broad ring shape around the center.

Atmospheric Outlook for the Forecast Period...The 1023 mb low-level ridge to the north will be knocked out in the next 24 hours by the 998 mb frontal cyclone and its vigorous shortwave upper trough currently racing east across eastern Canada and headed for the north Atlantic. This will cause Cristobal after 24 hours to rapidly accelerate east-northeast in deep-layered westerly flow south of the surface cold front trailing from the frontal cyclone and south of the frontal cyclone's vigorous upper trough. By the end of the forecast period...Cristobal is expected to transition into a large and strong non-tropical system supported by divergence on the southeast side of the upper trough....with the potential for the track to be rather fast and bend increasingly north when the back side of Cristobal's circulation pulls down the cooler air associated with the upper trough which makes the upper trough stronger/more amplified.

Thermodynamic Outlook for the Forecast Period...Cristobal has moved northward from waters of 30 deg C to waters that are 28 to 29 deg C. The updated faster forecast track shown below now predicts Cristobal will cross the 26 deg C isotherm into even cooler waters by Thursday. Dry air to the west of Cristobal remains strong due to strong upper convergence on the west side of the highly amplified western Atlantic upper trough Cristobal is currently interacting with. Perhaps thermodynamic parameters have become less favorable due to the above-noted arrival to lower sea surface temps and ingestion of some of this dry air...perhaps explaining why Cristobal has begun to struggle below the upper vortex as mentioned at the end of the above current prognosis section. These unfavorable thermodynamic parameters will no longer matter at the end of the forecast period since Cristobal's strength will be maintained by non-tropical processes by then.

 photo Aug_26_2014_H_Cristobal_Forecast_zps5be2780b.png

Track Forecast...Perhaps the 1023 mb low-level ridge to the north finally got a bit of influence on Cristobal as the storm has tracked a bit more leftward than yesterday's track guidance. Cristobal has also tracked a bit faster than previously forecast...causing me and the NHC to adjust the forecast track points to the north and west over the last 24 hours. I am a bit left of the 11 PM EDT NHC track forecast as Cristobal remains on a dead north course whereas the NHC forecast suggsested that Cristobal was supposed to be leaning north-northeast. I bend the track more northward than the NHC at the very end of the above-shown forecast in response to the likelihood of Cristobal amplifying an upper trough as mentioned at the very end of the above atmo outlook section. It is the presentation of the upper trough amplitude in model runs that caused me to bend the track more northward than the NHC at the end of the forecast period.

Intensity Forecast...I am below the 11 PM EDT NHC intensity guidance as it appears Cristobal is beginning to struggle with less favorable thermodynamic parameters and struggle below an upper vortex as mentioned in the last sentence of the above current prognosis section and as mentioned in the above thermodynamic outlook section.

Impact Forecast...The above-illustrated impact swath suggests that no land areas are forecast to received sustained winds of tropical storm force due to the forecast track...with the exception of southeastern Newfoundland which could experience tropical storm force winds on Friday morning. The swath is based on extrapolation of the 11 PM EDT NHC tropical storm wind field along my forecast track. Surf and rip currents will also be another effect of this storm as noted in impact statement (c) in the above forecast graphic.

...SPECIAL FEATURE...STRONG TROPICAL WAVE OVER WESTERN AFRICA...
Current Prognosis...Based on Africa satellite imagery...the tropical wave axis is estimated to be at 5W longitude with associated showers and thunderstorms covering eastern Guinea...eastern Sierra Leone...Liberia...Cote D'Ivoire...southwestern Burkina Faso...and the southwestern edge of Mali. The organization of the thunderstorms suggests the vorticity maximum of the tropical wave is located along 8N latitude. Comparing to satellite pictures 24 hours ago suggests the troipcal wave is moving at a brisk pace of about 12.5W longitude per day. However the track forecast below shows the westward pace slowing down to not stray too far from computer model runs which show a slower westward pace than this.

Atmospheric Outlook for the Forecast Period...The tropical wave is expected to take advantage of favorable tropical upper ridging (currently marked by blue-zig-zag in the lower-right in the atmo chart above). A central Atlantic upper ridge has been forming due to the latent heat release of Hurricane Cristobal and due to warm air advection ahead of a series of frontal cyclones supported by the western Atlantic upper trough. This central Atlantic upper ridge will be doubly enforced by warm air advection ahead of what is expected to be a large/vigorous non-tropical Cristobal later in the forecast period. A consequence of the central Atlantic upper ridge is that a tropical upper tropospheric trough (TUTT) has been consolidating in relatively lower pressures between the central Atlantic upper ridge and aforementioned tropical upper ridge. This system is expected to stay southeast of the unfavorable TUTT thru the forecast period.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over favorable 28 to 29 deg C waters upon entry into the Atlantic from Africa. On the forecast track below...temps will decrease to the 27 to 28 deg C range by the end of the forecast period...but this is still in the favorable range. This system is expected to develop in the moist air presently seen in the above thermo chart southeast of the dry Saharan air layer...and if it strengthens into a strong enough tropical cyclone prior to approaching the dry Saharan air it could develop a moisture field that fights off the dry air.

24 Hr Forecast (0000Z August 28)...Tropical wave emerging from western Africa with a tropical low located near 8N-17.5W

48 Hr Forecast (0000Z August 29)...Organized Tropical low located near 9N-25W...or south of the Cape Verde Islands

72 Hr Forecast (0000Z August 30)...35 mph maximum sustained wind tropical depression centered near 10.5N-31W...or southwest of the Cape Verde Islands

96 Hr Forecast (0000Z August 31)...45 mph max sustained wind tropical storm storm centered near 11.5N-36W

120 Hr Forecast (0000Z September 1)...60 mph max sustained wind troipcal storm centered near 13N-41W

2014 Atlantic Hurricane Season Birdseye Discussion #74

By: NCHurricane2009, 5:27 AM GMT on August 26, 2014

...TUESDAY AUGUST 26 2014 1:30 AM EDT...
Cristobal has intensified into the third hurricane of the 2014 Atlantic season earlier than expected this evening. The weather associated with Cristobal has finally lifted northward from the eastern Bahamas after dumping a few inches of rain over the islands...and now Cristobal is expected to accelerate northeastward over the western Atlantic. Because of its tendency to reform south and east toward the heavy thunderstorms sheared off to the south and east of the center...the forecast track guidance is now east enough such that Bermuda has issued a tropical storm watch. See special feature section below for additional details on Cristobal. Visit www.nhc.noaa.gov for up-to-the-minute the latest information on this system...including watches/warnings.

Tropical wave Invest 97-L midway between the Cape Verde Islands and Lesser Antilles is less organized than 24 hours ago and is struggling with the dry Saharan air to its north detected in the thermodynamics chart below. However their is continued attention from the NRL and NHC because conditions are generally favorable for development as the dry Saharan air layer is weaker relative to earlier this month and because this system will remain below favorable tropical upper ridging (currently marked by blue Hs in the eastern Atlantic in the atmospheric features chart below). The CMC model has withdrawn its support for developing this system in the vicinity of the Lesser Antilles in the timeframe that is now 96 hours away...instead developing it much later after crossing the Caribbean and into the Bay of Campeche (the ECMWF...or Euro...model also showed a similar solution today). However such a long range solution is unreliable. However the NAVGEM does suggest some development near the Lesser Antilles...and while the GFS also suggests some evolution near the Lesser Antilles it is only in the form of a vigorous tropical wave. I prefer to not upgrade this system to a special feature on this blog until their is more shorter range computer model support...or until this system shows signs of organization.

A vigorous tropical wave with widespread showers and thunderstorms over west-central Africa has been forecast to quickly develop when it reaches the eastern tropical Atlantic by the last three days worth of GFS computer model runs...predicted to occur in about 5 days. The Euro (ECMWF) meanwhile shows no development...while the CMC and NAVGEM show a broad tropical low as this system enters the Atlantic. I prefer not to upgrade this system to a special feature on this blog until we see how organized the wave is as it nears the west coast of Africa or until we see more computer models supporting the GFS solution. However interests in the Cape Verde Islands should monitor the progress of this tropical wave in case its circulation consolidates at a high enough latitude such that it passes over the islands instead of south of the islands.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_25_2014_2045Z_zps2fb011fd.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 1922Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_25_2014_2045Z_Thermo_zpsf2e14018.png
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...HURRICANE CRISTOBAL...
Current prognosis...As of the 11 PM EDT National Hurricane Center advisory...the center of Hurricane Cristobal was located at 25.1N-71.9W. In the past day Cristobal has been under northwesterly shear on the back side of the western Atlantic upper trough marked by a blue-dashed line north of Cristobal in the above atmospheric features chart. This caused the once-broad circulation of the storm to regenerate southeastward into intense storm bursts that have been sheared off...and with the center showing a more tight definition in satellite imagery additional reformation of the center is becoming less likely. The impressive intensity of the storm bursts appears to be due to very high upper-level divergence as the northwesterly upper flow over the storm splits while some of the flow turns westward across the south side of the eastern US upper ridge (marked by blue H and blue zig-zag lines in the above atmo chart) and the rest of the flow turns northeastward ahead of of the western Atlantic upper trough. Even though Cristobal doesn't look like a traditonal hurricane due to the presence of northwesterly shear across the storm...it appears the high amount of overhead upper divergence has allowed its surface pressures to fall enough to become a hurricane anyway as indicated by recon aircraft measurements.

Atmospheric Outlook for the Forecast Period...Northwesterly vertical shear induced by the western Atlantic upper trough has the potential to relax in the next 24 hours as the high intensity of Cristobal's thunderstorm mass maybe releasing enough latent heat to produce upper-level warming for the formation of a small upper anticyclone just southeast of the upper trough. Now that Cristobal is a strong/tall tropical cyclone...I currently expect Cristobal to track slowly north-northeast early in the forecast period while feeling the mid to upper flow on the east side of the western Atlantic upper trough. By second half of the forecast period...the 1003 mb frontal cyclone and its vigorous shortwave upper trough currently over south-central Canada will charge east across eastern Canada and into the north Atlantic...which will knock out the 1023 mb ridge to the north such that Cristobal rapidly accelerates east-northeast in deep-layered westerly flow south of the surface cold front trailing from the frontal cyclone and south of the frontal cyclone's vigorous upper trough. By the end of the forecast period...Cristobal is expected to transition into a non-tropical system supported by divergence on the southeast side of the upper trough....with the potential for the track to be rather fast and bend increasingly north when the back side of Cristobal's circualtion pulls down the cooler air associated with the upper trough which makes the upper trough stronger/more amplified.

Thermodynamic Outlook for the Forecast Period...Cristobal is currently over warm watrers in the 30 deg C range very supportive for additional strengthening in the early part of the forecast. This system will be tracking over waters above 26 deg C until Friday...when its expected to cross the 26 deg C isotherm into cooler waters. Dry air to the northwest of Cristobal has intensified as shown in the above thermodynamics chart...I believe in part due to the western Atlantic upper trough becoming more amplified due to the formation of an anticyclone over Cristobal immediately to the southeast of the upper trough (as discussed in the early part of the above atmo outlook section). With the upper trough more amplified...this promotes stronger upper convergence/sinking motion on the back side of the upper trough...hence the strengthening of the dry air. However I expect Cristobal to maintain strong storm activity with the support of the aforementioned anticyclone and instability brought on by the warm sea surface temperatures such that I do not expect this dry air to be an issue early in the forecast period...and by late in the forecast period the dry air will be irrelevant since Cristobal's strength will be maintained by non-tropical processes.

 photo Aug_25_2014_H_Cristobal_Forecast_zpsb452971f.png

Track Forecast...The continual eastward component of Cristobal's center reformation (as opposed to a pure southward or southwestward reformation) means that the storm no longer has the chance to bend west in track along the south side of the low-level ridge to the north before this ridge gets knocked out by 48 hours by the frontal cyclone mentioned in the above atmo outlook section. Therefore my updated track forecast above is a big rightward adjustment from my previous...and supports the idea of a north-northeast track turning and accelerating to the east-northeast as detailed in the above atmospheric outlook section. My updated track is a bit to the right of the NHC's 11 PM EDT as satellite suggested some additional eastward drifting of the center as it continues to sneak/reform beneath the strong thunderstorm canopy to the southeast. My updated track also remains behind the NHC's as Cristobal's southastward center reformation that has been going on over the last 24 hours has caused it to be behind schedule in regards to northward progression displayed in previous NHC forecasts (and yet the current NHC forecast shows the same rate of northward progression shown previously).

Intensity Forecast...Forecasting Cristobal to strengthen a bit more than the NHC showed at 11 PM EDT due to warm sea-surface temps in the 30 deg C range and with the expectation Cristobal forms a small shear-reducing/outflow enhancing upper anticyclone that covers at least the eastern half of the storm (details regarding this upper anticyclone mentioned in the early part of the above atmospheric outlook section). Later in the forecast period (Thursday and onward) I become below the 11 PM EDT NHC intensity guidance as I believe the westerly shear it encounters on the south side of the frontal cyclone's upper trough will be too high to support anything at hurricane force by Thursday. The rate of weakening after Thursday is shown to be slow as Cristobal transitions into a non-tropical entity supported by upper divergence on the southeast side of the frontal cyclone's upper trough.

Impact Forecast...The above-illustrated impact swath suggests that no land areas are forecast to received sustained winds of tropical storm force due to the forecast track...with the exception of Bermuda which is right on the edge of the swath. It is therefore wise for Bermuda to be under a tropical storm watch as any additional rightward shift in track would allow Bermuda to be in the swath...which would mean a brief period of tropical storm force winds on Wednesday. The swath is based on extrapolation of the 11 PM EDT NHC tropical storm wind field along my forecast track. Surf and rip currents will also be another effect of this storm as noted in impact statement (c) in the above forecast graphic.

2014 Atlantic Hurricane Season Birdseye Discussion #73

By: NCHurricane2009, 4:24 AM GMT on August 25, 2014

...MONDAY AUGUST 25 2014 12:25 AM EDT...
Tropical depression four has intensified into Tropical Storm Cristobal as of Sunday morning. A growing area of thunderstorms over the center last evening has been kept south of the center tonight due to developing northerly wind shear affecting Cristobal...causing rains to persist over the southeastern Bahamas. Peristent northerly shear could allow additional southern rain squalls to overspread parts of the Bahamas over the next day...and then this system is likely to accelerate northeastward over the western Atlantic according to the latest computer model runs...although a degree of uncertainty exists on the exact track this system takes in the western Atlantic. See special feature section below for additional details on Cristobal. Visit www.nhc.noaa.gov for up-to-the-minute the latest information on this system...including watches/warnings.

The tropical wave southwest of the Cape Verde Islands has been upgraded to Invest 97-L at the Naval Research Laboratory (NRL) of the US Navy and has become introduced National Hurricane Center (NHC) Tropical Weather Outlook...even though it is currently not organized and struggling a little bit with some of the dry Saharan air to its north detected in the thermodynamics chart below. The current attention from the NRL and NHC is because conditions are generally favorable for development as the dry Saharan air layer is weaker relative to earlier this month and because this system will remain below favorable tropical upper ridging (currently marked by blue H and blue zig-zag line in the eastern Atlantic in the atmospheric features chart below). Currently the usually aggressive CMC computer model is the only model that forecasts tropical cyclone formation...predicted to occur as this system reaches the Lesser Antilles in about 5 days (120 hours). I prefer to not upgrade this system to a special feature on this blog until more computer models jump on board...or until this system shows signs of organization.

A vigorous tropical wave with widespread showers and thunderstorms over central Africa has been forecast to quickly develop when it reaches the eastern tropical Atlantic by the last two days worth of GFS computer model runs...predicted to occur in about 6 days. I prefer not to upgrade this system to a special feature on this blog until we see how organized the wave is as it nears the west coast of Africa or until we see more computer models jumping on board.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_24_2014_2045Z_zps3157fb3f.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_24_2014_2045Z_Thermo_zps391e6b18.png
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 CRISTOBAL...
Current prognosis...As of the 11 PM EDT National Hurricane Center advisory...the center of Tropical Storm Cristobal was located at 24.8N-73.1W. As the atmospheric outlook section below details...this system is under a northwesterly vertical shear regime that is keeping the heaviest thunderstorms south and east of the center. The circulation appears to broad with multiple vortices inside. One of the prominent vortices appears to be further south of the 11 PM EDT advisory center fix...associated with a circular cluster of thunderstorms bringing rain over the southeastern Bahamas and located near 24N-72.5W.

Atmospheric Outlook for the Forecast Period...Inverted upper trough over the western Caribbean has moved into the southeastern Gulf of Mexico and is marked as a blue-dashed line in the above atmospheric features chart. Even though this upper trough is moving westward and away around the south side of the strong upper ridge over the eastern US (marked by blue H in the above atmo chart)...wind shear is not coming to an end and is shifting to a northwesterly vector as the western Atlantic upper trough to the north (marked by blue dashed line) will become amplified enough to leave behind a cut-off upper vortex to the northeast. The northwesterly shear is expected to finally reduce by 72 hours after the cut-off upper vortex shifts east. As far as steering is concerned...Cristobal in the early part of the forecast will be interacting with the 1024 mb Atlantic subtropical ridge to the east and 1023 mb high-latitude ridge nosing in from the north that is supported by upper convergence on the west side of the western Atlantic upper trough. By late in the forecast...a fragment of the current western US upper trough will have moved around the strong eastern US upper ridge and into eastern Canada while supporting/carrying the 1002 mb frontal cyclone currently over the north-central US/south-central Canada. As this frontal cyclone arrives into eastern Canada...it will weaken the ridge to the north and become a steering influence at the end of the forecast period.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over very favorable 30 deg C waters early in the forecast period...decreasing to a still-favorable 29 to 28 deg C range as this system accelerates northeastward late in the forecast period. The above thermo chart also shows the recent development of two patches of dry air...one over southern Florida associated with the non-divergent upper atmosphere asosciated with the southeastern Gulf inverted upper trough...and another offshore of the Carolinas assoicated with the western upper convergence of the western Atlantic upper trough. By 72 hours the upper trough is expected to have shifted eastward and away...allowing the dry air associated with its western upper convergent zone to also shift away.

 photo Aug_24_2014_TS_Cristobal_Forecast_zps33f7ce71.png

Track Forecast...My previous forecast track in discussion #72 showed a slow track bending to the west while influenced by the ridge to the north...followed by an acceleration to the northeast into the southwestern quadrant of the frontal cyclone mentioned at the end of the above atmospheric outlook section. However as computer models have been initialized with the lastest recon aicraft center fixes which showed a north track instead of a northwest track...this has become enough of a rightward adjustment for the models such that the models have begun predicting that Cristobal will continue straight north-northeast into the armpit between the ridge to the north and ridge to the east...positioning itself such that it rapidly accelerates northeastward on the southeast side of the frontal cyclone at the end of the forecast period. The National Hurricane Center has been adjusting their track to catch up with the rightward adjusmtent in the computer models. However I have been a bit reluctant to join this adjustment because the current circulation of Cristobal is broad...and so it has the potential to regenerate southward toward the circular storm burst and mini-vortex at 24N-72.5W noted in the above current prognosis section. If such a regeneration were to occur...it would still have potential to bend west in track along the south side of the ridge to the north rather than going straight north-northeast into the armpit between both ridges. Therefore my updated forecast track above is a blend between the 11 PM EDT NHC forecast and my previous forecast track in discussion #72.

Intensity Forecast...I initially keep the intensification rate slow due to forecast shear for the first 48 hours as outlined in the above atmospheric outlook section...and due to the dry air noted in the above thermodynamic outlook section. With the dry air and shear diminishing by 72 hours...I then forecast strengthening into a a hurricane (75+ mph maximum sustained winds). Weakening is shown by the end of the forecast as Cristobal will be entering westerly vertical shear induced by fast upper westerlies on the southwest side of the upper trough associated with the frontal cyclone mentioned at the end of the above atmo outlook section.

Impact Forecast...The above-illustrated impact swath suggests that no land areas are forecast to received sustained winds of tropical storm force due to the forecast track. The swath is based on extrapolation of the 11 PM EDT NHC tropical storm wind field along my forecast track...which I inflate in size to reflect a strengthening storm. A growing area of thunderstorms over the center last evening has been kept south of the center tonight due to developing northerly wind shear affecting Cristobal...causing rains to persist over the southeastern Bahamas. Peristent northerly shear could allow additional southern rain squalls to overspread parts of the Bahamas over the next day. As this system gathers strength...surf and rip currents will become an increasing threat as noted by impact statement (c) in the above forecast graphic.

2014 Atlantic Hurricane Season Birdseye Discussion #72

By: NCHurricane2009, 4:58 AM GMT on August 24, 2014

...SUNDAY AUGUST 24 2014 1:00 AM EDT...
Aircraft reconnaissance has finally found a closed circulation to upgrade Invest 96-L to a tropical cyclone. However because the maximum sustained winds measured were below storm force at the time...this system has been upgraded to tropical depression four. With the center expected to track east of the Bahamas...impacts across the island chain are not expected to be significant. The long range threat to the southeastern United States coast is a bit uncertain at this time...but the latest computer model runs favor a track turning away from the United States just beyond the forecast period. See special feature section below for additional details on this system. Visit www.nhc.noaa.gov for up-to-the-minute the latest information on this system...including watches/warnings.

A tropical wave has recently emerged from Africa into the eastern tropical Atlantic over the last couple of days...and reached a peak in organization as of 0600Z this morning while producing a semi-organized storm cluster southwest of the Cape Verde Islands...after which time the storm cluster has become less organized. Because the dry Saharan air layer is weaker relative to earlier this month and because this system will remain below favorable tropical upper ridging (currently marked by blue Hs in the eastern Atlantic in the atmospheric features chart below)...their is some potential for development as it tracks westward across the Atlantic tropics over the next few days...although current computer model support is weak.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_23_2014_2045Z_zps521e7c2f.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_23_2014_2045Z_Thermo_zps0e9b39aa.png
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 FOUR...
Current prognosis...As of the 11 PM EDT National Hurricane Center advisory...the center of newly formed tropical depression four was located at 22.3N-72.6W...or over the southeastern Bahamas. The center currently has a small ball of thunderstorms overhead...with most of the outer spiral bands of showers and thunderstorms located to the east of the center. Due to light westerly shear imparted by an inverted upper trough over the western Caribbean (marked by blue dashed line west of the depression in the above atmospheric features chart)...outer spiral bands are limited west of the center.

Atmospheric Outlook for the Forecast Period...Western Caribbean inverted upper trough mentioned in the above current prognosis section is expected to impart additional light westerly shear across this system for another 24 hours...after which time the upper trough will have moved westward and away around the south side of the strong upper ridge over the eastern US (marked by blue H in the above atmo chart). However the western Atlantic upper trough to the north (marked by blue dashed line) will become amplified enough to leave behind a cut-off upper vortex to the northeast expected to induce northerly shear across this system by 48 and 72 hours. Shear is expected to finally reduce by 96 and 120 hours after the cut-off upper vortex shifts east. Tropical depression four is currently moving northwest around the west side of the low-level Atlantic subtropical ridge marked by a red zig-zag line. In the middle of the forecast period...a building high-latitude ridge nosing in from the north...supported by upper convergence on the west side of the western Atlantic upper trough...will cause the track to bend more west-northwest (this high-latitude ridge is currently marked as a 1023 mb center over eastern Canada in the above atmo chart). By the end of the forecast...a fragment of the current western US upper trough will have moved around the strong eastern US upper ridge and into eastern Canada while supporting/carrying the 1005 mb frontal cyclone currently over the northwestern US. Between 96 and 120 hours this frontal cyclone will have weakened the ridge to the north such that the track of this system is expected to accelerate northward. The question is will this system go northeastward while getting dragged into the southwest side of the frontal cyclone...or will it turn northwestward due to the low-level ridge behind the frontal cyclone?

Thermodynamic Outlook for the Forecast Period...This system will be tracking over very favorable 30 to 31 deg C waters thru the forecast period. The above thermo chart also shows this system is located in a moist environemnt. Therefore thermodynamic parameters are very favorable for devlopment during the forecast period.

 photo Aug_23_2014_TD_Four_Forecast_CORRECTED_zps0971f51c.png

Track Forecast...The track forecast shown above is a continuation of my track forecast from discussion #71...with the exception of the early part of the forecast line which is displaced a bit westward as the circulation has consolidated further to the west relative to the track forecast I presented in discussion #71. Their is debate as to whether this system will go northwest or northeast at the end of the forecast period as outlined in the above atmospheric outlook section. Therefore as shown above I take a more neutral approach...but lean the track to the north-northeast because the more reliable GFS and ECMWF (Euro) runs from earlier on Saturday go with a northeast track.

Intensity Forecast...I initially keep the intensification rate slow due to forecast shear for the first 72 hours as outlined in the above atmospheric outlook section. With low shear and favorable thermodynamic conditions after that time...I forecast intensification to a hurricane (75+ mph maximum sustained winds).

Impact Forecast...The above-illustrated impact swath suggests that no land areas are forecast to received sustained winds of tropical storm force due to the forecast track keeping the center east of the Bahama island chain and east of the Florida peninsula. However with westerly shear expected to abate after 24 hours...outer feeder bands containing showers and thunderstorms are likely to begin filling the west side and overspread the central and western Bahamas by Monday and Tuesday. Feeder bands could continue overspreading the western Bahamas and potentially move into east-central Florida on Wednesday as northerly wind shear has the potential to push showers and thunderstorms to the south of the center. As this system gathers strength...surf and rip currents will become an increasing threat as noted by impact statement (c) in the above forecast graphic.

2014 Atlantic Hurricane Season Birdseye Discussion #71

By: NCHurricane2009, 3:46 AM GMT on August 23, 2014

...FRIDAY AUGUST 22 2014 11:47 PM EDT...
The circulation of disturbance Invest 96-L has re-organized to the southwest while becoming more vigorous within the last 24 hours...resutling in heavy weather spreading across Puerto Rico and the Dominican Republic. Aircraft reconaissance continues to find maximum winds of tropical storm force...and tropical storm formation is possible at any time as soon as reconaissance or surface observation confirm a closed circulation. Regardless of tropical storm formation or not...the heavy weather is likely to spread into Haiti and the Bahamas over the next day or so. See special feature section below for additional details on this disturbance.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_22_2014_2345Z_zps139e8d37.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_22_2014_2345Z_Thermo_zps59be339e.png
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 DISTURBANCE INVEST 96-L...
Current prognosis...Satellite animation this afternoon and evening suggests the circulation of this system has been lumbering at a location near 19N-69W...or along the north coast of the Dominican Republic. This location is further south and west than what was previously predicted for this timeframe as this system re-organized to the southwest. Therefore my updated forecast track below and the latest suite of computer model runs have made a westward shift relative to yesterday. The current circulation of this system is more vigorous than any circulation this system has previously displayed with an abundance of showers and thunderstorms in all quadrants producing heavy weather over Puerto Rico... the Dominican Republic...and adjacent tropical waters. Based on continued reconnaissance observations of tropical storm force winds...this system is almost a tropical storm and will be upgraded to one as soon as surface observations or reconnaissance can establish that the current circulation is closed.

Atmospheric Outlook for the Forecast Period...Upper trough over the western Atlantic as marked by a blue-dashed line in the atmospheric features chart above is weakening the west side of the low-level Atlantic subtropical ridge marked by a red-zig-zag line. Therefore this system will soon bend northward in track while steered around the west side of the ridge. By the latter part of the forecast period...this system is likely to move slowly while jammed between the west side of the Atlantic subtropical ridge and a building high-latitude ridge nosing in from the north supported by upper convergence on the west side of the upper trough (this high-latitude ridge is currently marked as a 1026 mb center over eastern Canada in the above atmo chart). However unlikely in my previous forecast where I stall this system in the armpit between both ridges...the southwestward relocation of this system now means it is likely to stay southwest of the armpit and instead move slowly west-northwest into the western Bahamas and toward the east coast of Florida while pushed by the ridge to the north. I flatten the intensity forecast during 72 to 96 hours as the latest model runs are showing a more amplified upper trough that leaves behind a cut-off upper vortex...and therefore I am still forced to forecast the system getting hit by some northerly wind shear despite having shifted the forecast track further southwest from the previous. However I show strengthening into a hurricane by 120 hours as the upper vortex will have shifted to the east...which will allow the shear to reduce.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over favorable 29 to 30 deg C waters thru the forecast period. Currently this system is sandwiched between the bulk of the dry Saharan air to layer to the east and a patch of eastern Caribbean dry air to the west as seen in the above thermo chart. However this system appears to have finally developed a strong enough circulation such that its surface convergence and upper divergence is producing a moisture field robust to the dry air.

24 Hr Forecast (1800Z August 23)...45 mph max sustained wind tropical storm centered near 21N-71W...or moving northwestward into the eastern Bahamas.

48 Hr Forecast (1800Z August 24)...60 mph max sustained wind tropical storm centered near 24N-72.5W...or just east of the central Bahamas.

72 Hr Forecast (1800Z August 25)...60 mph max sustained wind tropical storm under northerly shear centered near 25.5N-74W...or just east of the western Bahamas

96 Hr Forecast (1800Z August 26)...65 mph max sustained wind tropical storm under light norhterly shear centered near 26.5N-76W..or just east of Abaco Island in the Bahamas

120 Hr Forecast (1800Z August 27)...80 mph max sustained wind hurricane centered near 27.5N-78W...or just east of Florida and just north of the western Bahamas

2014 Atlantic Hurricane Season Birdseye Discussion #70

By: NCHurricane2009, 3:35 AM GMT on August 22, 2014

...THURSDAY AUGUST 21 2014 11:36 PM EDT...
Tropical disturbance Invest 96-L currently located east of the northern Lesser Antilles continues to track further north than expected. Therefore this system is likely to pass north of the northeastern Caribbean Islands and Bahamas...afterwards stalling in the western Atlantic for a period due to weak steering currents. Despite the more northern track...the southwestern outer squalls of this large system have arrived to the northern Lesser Antilles and Virgin Islands...and will spread into Puerto Rico...the Dominican Republic...and eastern Bahamas over the next day or so. See special feature section below for an updated assessment on this disturbance.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_21_2014_2245Z_zps88127069.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_21_2014_2245Z_Thermo_zps7d3562bc.png
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 DISTURBANCE INVEST 96-L...
Current prognosis...Between 1800Z and 0000Z...satellite animation suggests this system is now on a northwestward track while moving from 16.5N-57.5W to 17.5N-59.5W. This track is further north than expected...perhaps as the current ciruculation is being steered by the northeastern quadrant of what is a shadow of the original southwestern circulation. Therefore my updated forecast track below and the latest suite of computer model runs have made another northward shift relative to yesterday. Based on reconnaissance observations announced in a 4 PM EDT NHC Special Tropical Weather Outlook this past afternoon of winds at tropical storm force...this system is almost a tropical storm. Satellite has been showing a cloud swirl center with some outer spiral bands of thunderstorms especially to the south and west. The feeble level of storm activity perhaps is due to this system ingesting a patch of dry northeastern Caribbean air and some of the bulk of the dry Saharan air layer to the northeast seen in the above thermodynamics chart. Recently a small storm burst has begun directly over the cloud swirl center...and it remains to be seen if this burst expands such that this system finally gets upgraded to a tropical storm.

Atmospheric Outlook for the Forecast Period...Upper trough over the western Atlantic as marked by a blue-dashed line in the atmospheric features chart above will become re-enforced while merging with the 1013 mb frontal cyclone and associated upper trough currently currently marching offshore from the northeastern US. This upper trough will weaken the west side of the low-level 1022 mb Atlantic subtropical ridge such that the track of this system will bend more northward while steered around the west side of the ridge. By the end of the forecast period...this system is likely to stall while becoming jammed between the west side of the Atlantic subtropical ridge and a building high-latitude ridge nosing in from the north supported by upper convergence on the west side of the upper trough (this high-latitude ridge is in its formative stages as marked by the 1028 mb center over northeastern Canada in the above atmo chart). My updated intensity forecast below is lowered from my previous as the more northward forecast track now means this system will run into westerly and northerly shear on the south and west sides of the upper trough. By 120 hours however the upper trough should be moving eastward and away...which could allow the system to resume stregnthening by that time.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over favorable 29 to 30 deg C waters thru the forecast period. Currently this system is sandwiched between the bulk of the dry Saharan air to layer to the northeast and a patch of northeastern Caribbean dry air to the west as noted in the above current prognosis section. However as the above thermo chart shows...a continued northwestward track as forecast below will take this system to a more favorable moist environment currently covering eastern North America and waters offshore of the southeastern US.

24 Hr Forecast (1800Z August 22)...45 mph max sustained wind tropical storm centered near 20.5N-64W in the western Atlantic just north of the Virgin Islands.

48 Hr Forecast (1800Z August 23)...50 mph max sustained wind tropical storm under westerly shear centered near 26N-70W...or northeast of the eastern Bahamas.

72 Hr Forecast (1800Z August 24)...50 mph max sustained wind tropical storm under northwesterly shear centered near 29N-72.5W...or in the western Atlantic midway between the Bahamas and Bermuda.

96 Hr Forecast (1800Z August 25)...50 mph max sustained wind tropical storm under light northerly shear centered near 30N-75W

120 Hr Forecast (1800Z August 26)...65 mph max sustained wind tropical storm centered near 30N-75W

2014 Atlantic Hurricane Season Birdseye Discussion #69

By: NCHurricane2009, 3:09 AM GMT on August 21, 2014

...WEDNESDAY AUGUST 20 2014 11:15 PM EDT...
Tropical disturbance Invest 96-L currently located east of the Lesser Antilles has re-organized to the northeast while absorbing with the tropical wave to its east. Therefore this system is on a further north track now threatening the central and norhtern Lesser Antilles...the northeastern Caribbean Islands (Puerto Rico...the Virgin Islands...Haiti and the Dominican Republic)...the Bahamas...and then potentially the southeastern United States coast over the course of the next few days. See special feature section below for additional details on this developing situation.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_20_2014_2245Z_zps6942aa0e.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_20_2014_2245Z_Thermo_zps7fba7dd0.png
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 DISTURBANCE INVEST 96-L...
Current prognosis...Over the past 24 hours the circulation of this disturbance became elongated while merging with with the tropical wave previously to its east. Meanwhile the original tropical wave that spawned the circulation continued west and has dissipated over the Lesser Antilles as of 1200Z as marked in the above atmospheric features chart. Recently the circulation appears to have become much better organized and consolidated at a location northeast of where it was previously organizing. Because this rapidly organizing circulation is along the tropical wave axis that came in from the east...the same wave that was a special feature on this blog during discussions #66 and #67...one could argue this system is now a continuation of that special feature. The recent re-organization of the disturbance to the northeast while merging with the tropical wave to the east may have been what the computer models have been picking up on...and because this has materialized my updated forecast track below is now within the model consensus instead of being south of the model consensus like it was previously. Satellite animation suggests the organizing circulation has moved from 12.5N-52W as of 1800Z to 12.75N-53.5W as of 0000Z...or at a pace of 1.5W per 6 hours (or 6W per 24 hours) upon which the early part of the updated forecast track below is based upon. Because of the recent quick organization trend...I have moved the time of forecast tropical storm formation (40+ mph max sustained winds) to be sooner than previously forecast.

Atmospheric Outlook for the Forecast Period...Upper trough previously over the Lesser Antilles has moved northwestward into the western Atlantic as marked by a blue-dashed line in the atmospheric features chart above...and will continue northwestward and away while merging with the 1011 mb frontal cyclone and associated upper trough currently over the eastern US. This will allow the favorable tropical upper ridge (marked by blue-zig-zag line overhead of 96-L) to continue expanding westward such that 96-L remains under favorable low shear/enhanced outflow. As the current eastern US upper trough then shifts into the western Atlantic...a pattern of upper ridging over the eastern US/Gulf of Mexico and upper troughing in the western US will become established during the forecast period. The unfavorable Caribbean upper vorticity (marked by blue dashed line) will slowly retrograde westward around the south side of the eastern US/Gulf of Mexico upper ridge such that it also stays clear of this system. Therefore with low shear/good outflow thru the forecast period...I am encouraged to forecast a hurricane by 120 hours as shown below (the only time I suggest weakening is between 72 and 96 hours when this system is forecast to interact with the landmass of the Dominican Republic/Haiti). From 48 to 96 hours...the west end of the low-level Atlantic subtropical ridge is forecast to slowly weaken...first by the arrival of the current eastern US upper trogh/surface frontal cyclone into the western Atlantic...then by a series of central US frontal cyclones supported by the forecast western US upper trough...which is why the system is predicted to bend increasingly to the northwest in the latter part of the forecast below. By 120 hours the forecast track remains northwest instead of north in spite of the weaknesses associated with the western US upper trough and western Atlantic upper trough as upper convergence on the west side of the western Atlantic upper trough will be supporting a building high-latitude surface ridge that noses in from the north.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over favorable 28 to 29 deg C waters early in the forecast period...increasing to an even more favorable 30 to 31 deg C later in the forecast period. This system is currently moving away from the bulk of the dry Saharan air layer which is to the northeast...but as shown in the thermo chart above this system may have to contend with some small patches of dry air presently seen in the northern half of the Caribbean Sea. Currently it is assumed that the low-level convergence/upper divergence of this system will be vigorous enough to maintain a moisture field that does not become adversely affected by the patches of dry air.

24 Hr Forecast (1800Z August 21)...40 mph max sustained wind tropical storm centered near 13.5N-58W moving into the Lesser Antilles

48 Hr Forecast (1800Z August 22)...60 mph max sustained wind tropical storm centered near 14.5N-64W in the eastern Caribbean Sea

72 Hr Forecast (1800Z August 23)...70 mph max sustained wind tropical storm centered near 16.5N-69W...or just south of and moving toward the Dominican Republic

96 Hr Forecast (1800Z August 24)...65 mph max sustained wind tropical storm centered near 21N-73W...or approaching the southeastern Bahamas

120 Hr Forecast (1800Z August 25)...85 mph max sustained wind hurricane centered near 24.5N-77W...or over the western Bahamas

2014 Atlantic Hurricane Season Birdseye Discussion #68

By: NCHurricane2009, 3:36 AM GMT on August 20, 2014

...TUESDAY AUGUST 19 2014 11:40 PM EDT...
The tropical wave midway between the Lesser Antilles and Cape Verde Islands is now producing a new and organizing low pressure spin to the south of the dry Saharan air layer from which the CMC...GFS...and NAVGEM computer models forecast tropical cyclone development. This system has also been upgraded to Invest 96-L this evening. With this system now becoming a threat to develop...I have upgraded it to a special feature on this blog. Interests in the southern Lesser Antilles...Caribbean Sea...and Gulf of Mexico should monitor the progress of this system over the next few days. See special feature section below for additional details.

The tropical wave previously southwest of the Cape Verde Islands is now in the waters midway between the Cape Verde Islands and Lesser Antilles...and has beocome less organized behind Invest 96-L. Therefore I have dropped it as a special feature on this blog...and the National Hurricane Center is likely to cancel it in their Tropical Weather Outlook if current trends continue.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_19_2014_2045Z_zps2c73a02c.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_19_2014_2045Z_Thermo_zps2d713a76.png
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 96-L...
Current prognosis...As of 1800Z the National Hurricane Center has marked a tropical wave axis at 50W longitude...with this system producing a new 1009 mb low pressure spin at the south end of the tropical wave and already showing early signs of organized spiral banding in the associated showers and thunderstorms. Between 1800Z and 0000Z satellite animation shows the circulation moving from 10N-50W to 10N-51W...or at a rate of 1W per 6 hours (4W per 24 hours) upon which the early part of my track forecast below is based on. The westward pace of my later forecast track is a bit faster than that to stay in closer agreement with the faster westward progression shown in some of the models (such as the GFS) that develop this system. However my forecast track below is also generally south of many of this evening's model runs as many of the models show this system consolidating further to the north than what current satellite observations suggest.

Atmospheric Outlook for the Forecast Period...A central Atlantic upper trough has moved westward into the Lesser Antilles as marked by a blue-dashed line in the atmospheric features chart above...and will be moving northwestward and away while merging with the 1002 mb frontal cyclone and associated upper trough currently over the central US. This will allow the favorable tropical upper ridge (marked by blue-zig-zag line overhead of 96-L) to continue expanding westward such that 96-L remains under favorable low shear/enhanced outflow as it marches into the Caribbean Sea. Meanwhile over the US...expect a pattern of upper ridging over the eastern US/Gulf of Mexico and upper troughing in the western US to become established during the forecast period. The unfavorable western Caribbean upper vorticity (marked by blue L) will slowly retrograde westward around the south side of the eastern US/Gulf of Mexico upper ridge such that it also stays clear of this system. Therefore with low shear/good outflow thru the forecast period...I am encouraged to forecast a hurricane by 120 hours as shown below. From 72 to 120 hrs...the west end of the low-level Atlantic subtropical ridge is forecast to slowly weaken...first by the arrival of the central US upper trough/surface 1002 mb frontal cyclone into the western Atlantic...then by a series of central US frontal cyclones supported by the forecast western US upper trough...which is why the system is predicted to bend increasingly to the northwest in the latter part of the forecast below. Such a steering pattern is likely to cause this system to continue northwest into the Gulf of Mexico from the Caribbean in the very long range outside the forecast period.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over favorable 28 deg C waters early in the forecast period...increasing to an even more favorable 29 to 30 deg C later in the forecast period. The dry Saharan air layer seen in the thermo chart above no longer appears to be a problem for development as this system is organizing within the moisture field of the ITCZ (Intertropical Convergence Zone) to the south of the dry Saharan air layer.

24 Hr Forecast (1800Z August 20)....Organized tropical low pressure centered near 10.5N-54W.

48 Hr Forecast (1800Z August 21)...35 mph max sustained wind tropical depression centered near 11N-58W moving into the southern Lesser Antilles

72 Hr Forecast (1800Z August 22)...45 mph max sustained wind tropical storm centered near 11.5N-62W departing from the southern Lesser Antilles and entering the southeastern Caribbean Sea

96 Hr Forecast (1800Z August 23)...60 mph max sustained wind tropical storm centered near 12.5N-67W moving west-northwest toward the central Caribbean Sea

120 Hr Forecast (1800Z August 24)...75 mph max sustained wind hurricane centered near 15N-72W moving northwest across the central Caribbean toward Jamaica

2014 Atlantic Hurricane Season Birdseye Discussion #67

By: NCHurricane2009, 2:40 AM GMT on August 19, 2014

...MONDAY AUGUST 18 2014 10:40 PM EDT...
The slow pace of the 2014 Atlantic Hurricane Season continues as vigorous tropical waves emerging from Africa run into unfavorable conditions in the central tropical Atlantic. The following is an update on the current tropical waves in the Atlantic...

The tropical wave previously west-southwest of the Cape Verde Islands is now midway between the Cape Verde Islands and Lesser Antilles. Even though it remains in the National Hurricane Center Tropical Weather Outlook...it continues to lack significant showers and thunderstorms due to dry Saharan air seen in the thermodynamics chart below. The central Atlantic upper trough marked by a blue dashed line in the atmospheric features chart below is shifting westward around the south side of the central Atlantic upper ridge (marked by blue H)...which has allowed this tropical wave to be below a favorable tropical upper ridge (marked by blue-zig-zag line) expanding from the eastern Atlantic in the wake of the upper trough. However this system is still not likely to develop due to the dry air.

The tropical wave southwest of the Cape Verde Islands remains a special feature on this blog...see special feature section below for details. It has also been introduced into the National Hurricane Center Tropical Weather Outlook this evening. However I may cancel it as a special feature in my next blog update as it now appears could also be inhibited by dry Saharan air and interaction with an unfavorable upper vortex late in the forecast period.

Tropical low Invest 95-L has seen a recovery in thunderstorms as it begins to move west and pass just south of the Cape Verde Islands. Meanwhile another vigorous tropical wave is currently over western Africa and is expected to emerge into the Atlantic tropical waters within the next 24 hours. What remains of Invest 95-L and this tropical wave have a high chance of merging due to their close proximity. Development of this combined system is possible in favorable atmospheric conditions east of the forecast upper vortex mentioned in the previous paragraph and will depend on the state of the dry Saharan air layer as this system marches across the tropical Atlantic.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_18_2014_2045Z_zps1d11515c.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_18_2014_2045Z_Thermo_zpsfd5eae1f.png
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 SOUTHWEST OF THE CAPE VERDE ISLANDS...
Current prognosis...As of 1800Z the National Hurricane Center has marked a tropical wave axis at 33W longitude...with this system recently creating a leaving behind a 1010 mb low pressure spin near 12.5N-30W. Satellite imagery is showing an associated rotating area of showers and thunderstorms over the south end of the tropical wave axis and just west of the low pressure spin. The updated forecast below is based on evolving the tropical low into a tropical cyclone as the tropical low so far has been following the previous forecast laid out in discussion #66. I have also delayed the time of forecast tropical cyclone formation to 96 hours from now as the system has not become any better organized within the last day. In fact satellite animation suggests the spin of this system is elongated east-west such that will take some time to consolidate into a focused spin.

Atmospheric Outlook for the Forecast Period...System will be steered westward by 1020 mb Atlantic low-level subtropical ridge to the north thru the forecast period. The central Atlantic upper trough marked by a blue dashed line in the above atmo chart will continue to retrograde westward around the central Atlantic upper ridge (marked by blue H) thru the early part of the forecast period...allowing this system to potentially take advantage of low shear/good outflow below a tropical upper ridge in the eastern Atlantic (marked by blue-zig-zag line) expanding in the wake of the upper trough. In the second half of the forecast period (72 to 120 hrs)...what is now the mid-latitude upper trough and 1006 mb frontal cyclone over the north-central US will be emerging into the western Atlantic whose surface warm air advection will build up the western part of the tropical upper ridge into an anticyclone to the northwest of the system...with a fragment of the central Atlantic upper trough potentially orbiting around the anticyclone and becoming a cut-off upper vortex just northwest of this system. Current forecast below assumes this system will become a weak tropical cyclone under southerly shear at a location just southeast of the upper vortex by 96 hours...then will be sheared apart as it moves closer to the upper vortex by 120 hours.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over favorable 27 to 28 deg C water thru the forecast period. Dry Saharan air lies north and west as the above thermo chart shows...and the tropical wave to the west has potentially not done a good enough job of moistening the environment ahead such that their is uncertainty as to whether or not this system will survive the interaction with dry air.

24 Hr Forecast (1800Z August 19)....Tropical low pressure centered near 12.5N-35W.

48 Hr Forecast (1800Z August 20)...Tropical low pressure centered near 12.5N-40W

72 Hr Forecast (1800Z August 21)...Organized tropical low pressure centered near 12.5N-45W

96 Hr Forecast (1800Z August 22)...35 mph max sustained wind tropical depression centered near 13N-50W under southerly vertical shear

120 Hr Forecast (1800Z August 23)...Remnant low pressure centered near 13.5N-55W.

2014 Atlantic Hurricane Season Birdseye Discussion #66

By: NCHurricane2009, 8:36 PM GMT on August 17, 2014

...SUNDAY AUGUST 17 2014 4:38 PM EDT...
The tropical wave west-southwest of the Cape Verde Islands continues to lack significant showers and thunderstorms...but continues to produce a low pressure spin currently located near 12N-40W and therefore has been introduced into the National Hurricane Center Tropical Weather Outlook. The central Atlantic upper trough marked by a blue dashed line in the atmospheric features chart below is shifting westward around the south side of the central Atlantic upper ridge (marked by blue H)...which has recently allowed this tropical wave to be in a more favorable environment below a tropical upper ridge (marked by blue-zig-zag line) expanding from the eastern Atlantic in the wake of the upper trough. However this system is still not likely to develop while ingesting the dry Saharan air layer presently to the north and west of the system.

Tropical low pressure spin Invest 95-L has been cancelled from the National Hurricane Center Tropical Weather Outlook but remains posted as an active feature on the Naval Research Laboratory site of the US Navy. Because it lacks showers and thunderstorms...this spin is hard to define on infrared satellite imagery but is well-defind on visible satellite as a shallow cloud swirl east of the Cape Verde Islands. Curiously this low pressure spin has become stationary...perhaps due to the combination of the low-level ridge weakening to the north due to the deepening 1001 mb frontal cyclone in the northeast Atlantic and the tug of the low pressure field of the African tropical wave to the east mentioned in the next paragraph. Meanwhile the parent tropical wave that produced this low pressure spin continues west and is producing concentrated showers and thunderstorms at a location southwest of the Cape Verde Islands. Because their is computer model support from the recent 06Z GFS and 00Z ECMWF (Euro) model runs and because this tropical wave will remain in a favorable environment below an expanding tropical upper ridge in the eastern Atlantic (marked by blue-zig-zag line in the atmo chart below)...I have upgraded this tropical wave to a special feature on this blog. See special feature section below for additional details.

Another vigorous tropical wave is currently over interior western Africa and is expected to emerge into the Atlantic tropical waters by 48 hours. This system will be in a favorable low shear/enhanced outflow environment below a tropical upper ridge expanding in the eastern Atlantic (marked by blue-zig-zag line in the atmo chart below) and therefore could become another concern for development this upcoming week.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_17_2014_1445Z_zps423f536e.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z and the 1327Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_17_2014_1445Z_Thermo_zpsaf2aa087.png
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 SOUTHWEST OF THE CAPE VERDE ISLANDS...
Current prognosis...As of 1200Z the National Hurricane Center has marked a tropical wave axis at 25W longitude...with satellite imagery showing an associated concentrated area of showers and thunderstorms southwest of the Cape Verde Islands.

Atmospheric Outlook for the Forecast Period...The deepening 1001 mb frontal cyclone in the northeastern Atlantic will continue to shift east...allowing the Atlantic low-level subtropical ridge to rebuild which is why I gradually accelerate the currently sluggish westward track of this system in my forecast below. The central Atlantic upper trough marked by a blue dashed line in the above atmo chart will continue to retrograde westward around the central Atlantic upper ridge (marked by blue H) thru the early part of the forecast period...allowing this system to potentially take advantage of low shear/good outflow below a tropical upper ridge in the eastern Atlantic (marked by blue-zig-zag line) expanding in the wake of the upper trough. At the very end of the forecast period (96 to 120 hrs)...a vigorous mid-latitude upper trough emerging from the eastern US is expected to support a surface frontal cyclone entering the western Atlantic whose surface warm air advection will build up the western part of the tropical upper ridge into an anticyclone to the northwest of the system...with a fragment of the central Atlantic upper trough potentially orbiting around the anticyclone and becoming an inverted upper trough just northwest of this system. Current forecast below assumes this system will not be adversely affected by this inverted upper trough while staying just southeast of the inverted upper trough by 120 hours.

Thermodynamic Outlook for the Forecast Period...This system is currently over favorable 28 deg C water...with the forecast track shown below taking this system across 27 to 28 deg C water thru the forecast period. Even though a batch of dry Saharan air lies north and west...the above thermo chart shows this dry air is currently weaker relative to the past few days and it is currenty assumed the tropical wave to the west of this system will also aid in moistening the environemnt ahead.

24 Hr Forecast (1200Z August 18)...Tropical wave axis at 28.5W longitude with concentrated cluster of showers and thunderstorms at the south end of the axis.

48 Hr Forecast (1200Z August 19)....Tropical wave axis at 33W longitude with concentrated cluster of showers and thunderstorms at the south end of the axis. Tropical low pressure spin forming at the south end of the tropical wave axis near 12.5N-33W.

72 Hr Forecast (1200Z August 20)...Organized tropical low centered near 12.5N-38W

96 Hr Forecast (1200Z August 21)...35 mph max sustained wind tropical depression centered near 13N-43W

120 Hr Forecast (1200Z August 22)...45 mph max sustained wind tropical storm centered near 13.5N-48W

2014 Atlantic Hurricane Season Birdseye Discussion #65

By: NCHurricane2009, 3:37 PM GMT on August 16, 2014

...SATURDAY AUGUST 16 2014 11:40 AM EDT...
The vigorous tropical wave west-southwest of the Cape Verde Islands continues to lack showers and thunderstorms while under a central Atlantic upper trough as marked by a blue dashed line in the atmospheric features chart below. This upper trough is later expected to shift westward around the south side of the central Atlantic upper ridge (marked by blue H)...which will allow this system to be in a marginally favorable light southerly shear environment on the east side of the upper trough...or even in a more favorable environment below a tropical upper ridge to expand from the eastern Atlantic in the wake of the upper trough. However this system is still not likely to develop while ingesting the dry Saharan air layer presently to the west of the system.

The vigorous tropical wave previously emerging from western Africa became very well organized and was upgraded to Invest 95-L overnight. Recently the tropical wave has become disorganized while moving into the Cape Verde Islands and has tracked northwestward toward unfavorable thermodynamic conditions (water temperatures below 26 deg C and dry Saharan air) more than expected...and therefore I have cancelled it as a special feature on this blog. The northwestward track will bend back to the west as the ridge weakness associated with the 1010 mb frontal cyclone moving into the northeast Atlantic becomes replaced by a building low-level ridge behind the frontal cyclone. Therefore this system will begin to re-enter waters at or above 26 deg C by 72 hours in the vicinity of 19N-35W. Development of this system beyond 72 hours will depend on the state of the dry Saharan air layer in the environment ahead of 19N-35W and how intact this system remains after traversing through the intially unfavorable thermodynamic conditions.

Another vigorous tropical wave is currently over interior western Africa and is expected to emerge into the Atlantic tropical waters by 72 hours. This system will be in a favorable low shear/enhanced outflow environment below a tropical upper ridge expanding in the eastern Atlantic and therefore could become a concern for development next week.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_16_2014_0615Z_zpsfa3c0936.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0600Z and the 0725Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_16_2014_0615Z_Thermo_zpsa984eb7a.png
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).

2014 Atlantic Hurricane Season Birdseye Discussion #64

By: NCHurricane2009, 5:46 AM GMT on August 15, 2014

...FRIDAY AUGUST 15 2014 1:45 AM EDT...
The vigorous tropical wave previously south of the Cape Verde Islands is currently southwest of the islands. Meanwhile a central Atlantic upper trough...as marked by a blue dashed line in the atmospheric features chart below...is shifting south in advance of a building central Atlantic upper ridge as marked by a blue H. The southward digging of the central Atlantic upper trough is creating a split in the low-latitude tropical upper ridging that has resulted in the formation of an inverted upper trough in the split and to the west of the tropical wave. Even though the tropical wave has recently formed a low pressure spin...it has also recently lost thunderstorm activity while sliding beneath the inverted upper trough (which has temporarily closed off into an upper vortex as marked by a blue L over the south part of the tropical wave). Expect the southward digging central Atlantic upper trough and inverted upper trough to merge in the next 24 hours overhead of the tropical wave...which will continue to suppress development of this system. As the combined upper trough later shifts westward around the south side of the central Atlantic upper ridge...this may allow this system to be in a marginally favorable light southerly shear environment on the east side of the upper trough...or even in a more favorable environment below a tropical upper ridge to expand from the eastern Atlantic in the wake of the upper trough. However this system is still not likely to develop while ingesting the dry Saharan air layer presently to the north and west.

The vigorous tropical wave previously over western Africa is emerging over the eastern tropical Atlantic waters while well-organized. I have upgraded it to a special feature on this blog with the expectation that it will become the next tropical cyclone in the Atlantic basin. Interests in the Cape Verde Islands should monitor the progress of this system as it is expected to pass just south of the islands. See special feature section below for additional details on this system.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_14_2014_2145Z_zps3af5bbc6.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 1915Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_14_2014_2145Z_Thermo_zps067af42c.png
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 EMERGING FROM WESTERN AFRICA...
Current prognosis...As of 0000Z infrared satellite imagery suggested that the tropical wave emerging from western Africa features spiral bands of showers and thunderstorms organizing around a low pressure spin centered near 12.5N-17.5W.

Atmospheric Outlook for the Forecast Period...A northwestern Atlantic low pressure has deepend from 1013 to 1008 mb in the last 24 hours while becoming re-enforced by the vigorous 1002 mb frontal cyclone and associated upper trough over eastern North America...which will cause this low to weaken the Atlantic low-level subtropical ridge as it shifts into the eastern Atlantic during the next 96 hours. Therefore my forecast below slows the westward track and deflects it a bit northward as the ridge weakens. By 120 hours the low-level ridge is forecast to rebuild which is why my final forecast point suggests a track bending more westward with an increase in forward speed. In the upper layers...a central Atlantic upper ridge is pushing a central Atlantic upper trough southward...which is later expected to retrograde westward around the south side of the upper ridge. However because this system is expected to take a slow westward track...it is expected to stay in a favorable low shear/good outflow environment associated with a tropical upper ridge to expand in the eastern tropical Atlantic in the wake of the retrograding upper trough.

Thermodynamic Outlook for the Forecast Period...The forecast track below will take the circulation center of this system along a 27 deg C sea-surface temperature isotherm. This will allow the northern part of the circulation to interact with less favorable water temps at or below 26 deg C until 120 hours when this system will be tracking into warmer waters. The potential interaction with milder waters to the north for the first 96 hours and dry Saharan air also to the north makes me show a gradual as opposed to rapid strengthening in my forecast below.

24 Hr Forecast (0000Z August 16)...Organized tropical low centered just southeast of the Cape Verde Islands near 12.5N-20.5W.

48 Hr Forecast (0000Z August 17)....40 mph max sustained wind tropical storm centered just south of the Cape Verde Islands near 12.5N-24W.

72 Hr Forecast (0000Z August 18)...45 mph max sustained wind tropical storm centered just southwest of the Cape Verde Islands near 13N-26.5W

96 Hr Forecast (0000Z August 19)...50 mph max sustained wind tropical depression centered near 14N-29W

120 Hr Forecast (0000Z August 20)...60 mph max sustained wind tropical storm centered near 14N-33W

2014 Atlantic Hurricane Season Birdseye Discussion #63

By: NCHurricane2009, 3:58 AM GMT on August 14, 2014

...WEDNESDAY AUGUST 13 2014 11:59 PM EDT...
Tropical wave Invest 94-L midway between the Lesser Antilles and Cape Verde Islands has continued to become less organized while ingesting dry air to the north and west and therefore tropical cyclone formation from this system is no longer likely. Therefore I have cancelled this system as a special feature on this blog.

The vigorous tropical wave previously southeast of the Cape Verde Islands has moved southwestward to a location south of the islands perhaps while interacting with the circulation of the vigorous tropical wave to the east mentioned in the next paragraph. Meanwhile a Tropical Upper Tropospheric Trough (TUTT) is present in the central Atlantic as marked by a blue L and pair of blue dashed lines in the atmospheric features chart below...and is expected to shift south in advance of a building central Atlantic upper ridge. The recent southwest track as opposed to a westward track means that this tropical wave is behind in its westward progression than previously thought...which indicates that it is more likely to stay east of the southward shifting TUTT rather than directly below it. However still not expecting additional development from this tropical wave as it will likely deal with less favorable southerly vertical shear on the east side of the southward shifting TUTT.

The vigorous tropical wave over western Africa will emerge into the Atlantic tropical waters in the next 24 hours. Meanwhile the deep-layered 1013 mb northwestern Atlantic low pressure marked in the atmospheric features chart below will become re-enforced by the vigorous 1002 mb frontal cyclone and associated upper trough over eastern North America...which will cause the deep-layered low to weaken the Atlantic low-level subtropical ridge as it shifts into the eastern Atlantic. As the ridge weakens...this will keep the westward progression of this tropical wave slow such that it has a very high chance to stay in a favorable low shear/good outflow environment associated with a tropical upper ridge to expand in the eastern tropical Atlantic in the wake of the TUTT mentioned in the previous paragraph. Therefore if this tropical wave continues to stay organized while moving over water...I will consider upgrading it to a special feature in my next blog update.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_13_2014_2045Z_zpse1a4e026.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_13_2014_2045Z_Thermo_zps8f8e9af9.png
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).

Hurricane

2014 Atlantic Hurricane Season Birdseye Discussion #62

By: NCHurricane2009, 3:48 AM GMT on August 13, 2014

...TUESDAY AUGUST 12 11:55 PM EDT...
Tropical wave Invest 94-L has become less organized due to dry air while moving into the waters midway between the Cape Verde Islands and Lesser Antilles. See special feature section below for an update on this tropical wave.

Two additional vigorous tropical waves are located behind Invest 94-L. The first has just moved offshore from Africa and is currently located just southeast of the Cape Verde Islands...and is not expected to develop as it will get caught in unfavorable upper-level convergence associated with the TUTT (Tropical Upper Tropospheric Trough) forecast to sag southward over the next few days (see atmospheric outlook section of the Invest 94-L special feature section for more info on the TUTT). The second tropical wave is located over interior western Africa and will emerge into the Atlantic tropical waters in about 48 hours...and has a better chance to develop below favorable low shear/good outflow associated with a tropical upper ridge to expand in the eastern tropical Atlantic in the wake of the aforementioned TUTT.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_12_2014_2045Z_zpsc5cacfa9.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_12_2014_2045Z_Thermo_zpsb616698c.png
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 94-L...
Current prognosis...As of 1800Z the NHC TAFB has defined a weak 1012 mb low pressure spin centered near 13N-37W in association with the vigorous tropical wave currently located midway betwen the Lesser Antilles and Cape Verde Islands. Overall shower and thunderstorm activity has become less organized and confined to the southern part of the circulation while this system battles the dry Saharan air layer located to the north and west. In my updated forecast below I have delayed forecast tropical cyclone formation to the timeframe that is 72 hours from now as this system has become less organized in the last day.

Atmospheric Outlook for the Forecast Period...Thru the forecast period this system will be steered west around the south side of the low-level 1028 mb Atlantic subtropical ridge marked in the atmospheric features chart above...with a bend toward the west-northwest at the very end of the forecast period while arriving to the southwestern quadrant of the low-level ridge. As the chart above also shows...their is a Tropical Upper Tropospheric Trough (TUTT) north of the system marked by a series of blue dashed lines and blue Ls. This system is currently in a favorable low shear/good upper outflow environment in a tropical upper ridge south of the TUTT as marked by a blue-zig-zag line. By the middle of the forecast period...the TUTT is forecast to shift south ahead of a building upper ridge in the central Atlantic. However this system is moving fast enough to the west such that it will escape the southward-shifting TUTT and arrive beneath more favorable upper ridging to persist over the eastern Caribbean Sea. Unfavorable upper vorticity persists in the western Caribbean Sea as marked by a blue-dashed line...and this vorticity is forecast to persist thru the forecast period such that it could disrupt this system at the very end of the forecast period which is why my updated forecast below develops this system slower than previously shown.

Thermodynamic Outlook for the Forecast Period...This system is currently battling dry Saharan air located to the north and west as mentioned in the above current prognosis section. Thru the forecast period the westward track of this system will take it from waters that are currently 27 deg C to waters that are 28 to 29 deg C. The current assumption in my updated forecast below is that the increasingly warm waters will give this system enough instability to fight off the dry air such that it develops into a tropical cyclone by 72 hours.

24 Hr Forecast (0000Z August 14)...Tropical low centered near 13.5N-45W.

48 Hr Forecast (0000Z August 15)....Tropical low centered near 13.5N-53W.

72 Hr Forecast (0000Z August 16)...30 mph max sustained wind tropical depression centered near 14N-60W crossing the Lesser Antilles.

96 Hr Forecast (0000Z August 17)...35 mph max sustained wind tropical depression centered near 14.5N-67W in the eastern Caribbean Sea.

120 Hr Forecast (0000Z August 18)...40 mph max sustained wind tropical storm centered near 15.5N-72W in the central Caribbean Sea.

2014 Atlantic Hurricane Season Birdseye Discussion #61

By: NCHurricane2009, 2:32 AM GMT on August 12, 2014

...MONDAY AUGUST 11 2014 10:33 PM EDT...
Vigorous tropical wave Invest 94-L currently southwest of the Cape Verde Islands has not become better organized but still has the potential to develop further...therefore the Lesser Antilles should monitor this system over the next few days. See special feature section below for additional details on Invest 94-L. It is quiet elsewhere in the Atlantic tropics.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_11_2014_2045Z_zpsfc56a12d.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 1921Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_11_2014_2045Z_Thermo_zps3cfac407.png
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 94-L...
Current prognosis...As of 1800Z the NHC TAFB has defined a 1012 mb low pressure spin centered near 11.5N-31W in association with the vigorous tropical wave currently located southwest of the Cape Verde Islands. The most organized shower and thunderstorm activity is to the southwest of the identified center...and this system has been moving faster to the west than previously forecast. Therefore my updated forecast below moves this system faster to the west...especially if this system re-generates a new center in the more organized activity southwest of the center. Have delayed forecast tropical cyclone formation to the timeframe that is 72 hours from now as this system has not become better organized in the last day.

Atmospheric Outlook for the Forecast Period...Thru the forecast period this system will be steered west around the south side of the low-level 1028 mb Atlantic subtropical ridge marked in the atmospheric features chart above. As the chart above also shows...their is a Tropical Upper Tropospheric Trough (TUTT) is forming as marked by a series of blue dashed lines and blue Ls to the north of this system. This system is increasingly finding itself in a favorable low shear/good upper outflow environment in a tropical upper ridge beginning to solidify south of the TUTT. By the end of the forecast period...the TUTT is forecast to shift south ahead of a building upper ridge in the central Atlantic. However with this system now forecast to move faster to the west than previously thought (as noted in the above current prognosis section)...it is now likely to escape the southward-shifting TUTT and slide beneath more favorable upper ridging to persist over the eastern Caribbean Sea.

Thermodynamic Outlook for the Forecast Period...As this system continues west it is beginning to encounter the swath of dry Saharan air that has recently killed off the tropical waves out ahead of this system. However animation of the above thermo chart suggests this tropical wave has so far been able to maintain its moisture field while beginning to push into the dry air. As far as sea-surface temperatures...the tropical wave will be tracking over 27 to 28 deg C early in the forecast period...increasing to 29 deg C while entering the eastern Caribbean Sea...temperatures on the favorable side for tropical development.

24 Hr Forecast (0000Z August 13)...Tropical low centered near 11.5N-39W.

48 Hr Forecast (0000Z August 14)...Tropical low centered near 11.5N-47W.

72 Hr Forecast (0000Z August 15)....35 mph max sustained wind tropical depression centered near 12N-55W.

96 Hr Forecast (0000Z August 16)...45 mph max sustained wind tropical storm centered near 12N-62W crossing the southern Lesser Antilles.

120 Hr Forecast (0000Z August 17)...50 mph max sustained wind tropical storm centered near 12.5N-69W in the southeastern Caribbean Sea.

2014 Atlantic Hurricane Season Birdseye Discussion #60

By: NCHurricane2009, 4:45 AM GMT on August 11, 2014

...MONDAY AUGUST 11 2014 12:46 AM EDT...
The strong tropical wave previously over interior western Africa has emerged into the eastern tropical Atlantic waters south-southeast of the Cape Verde Islands. The disturbance has been introduced into the National Hurricane Center Tropical Weather Outlook and has been upgraded to Invest 94-L on the Naval Research Laboratory Site of the US Navy. See special feature section below for additional details on this system.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_10_2014_1945Z_zps63707406.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 1928Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_10_2014_1945Z_Thermo_zpscd7d0558.png
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 94-L...
Current prognosis...As of 1800Z the NHC TAFB has defined a 1010 mb low pressure spin centered near 11N-22W associated with our strong tropical wave that has recently emerged from western Africa. Their is a large amount of surrounding showers and thunderstorms loosely organized around this low pressure spin. Therefore my current forecast for this system shown below gives it 72 hours before becoming a tropical cyclone with the assumption that this is a large system that will take some time to consolidate.

Atmospheric Outlook for the Forecast Period...Thru the forecast period this system will be steered west around the south side of the low-level 1026 mb Atlantic subtropical ridge marked in the atmospheric features chart above. As the chart above also shows...upper vorticity marked by blue-dashed lines and blue Ls is located in the central tropical Atlantic...northeastern Atlantic... and northwestern Atlantic. Over the next few days...this upper vorticity is forecast to merge into a Tropical Upper Tropospheric Trough (TUTT) with the tropical wave finding itself in a favorable low shear/good upper outflow environment in a tropical upper ridge to solidfy south of the TUTT. However by the end of the forecast period...the TUTT is forecast to shift south ahead of a building upper ridge in the central Atlantic. It is uncertain whether or not this system will be able to escape the unfavorable TUTT as it shifts south...which is why I develop the system slowly at the end of my forecast shown below.

Thermodynamic Outlook for the Forecast Period...As this system continues west it will encounter the swath of dry Saharan air that has recently killed off the tropical waves out ahead of this system. The current assumption is that the dry air will not be an issue because this tropical wave is stronger and more organized than the recent previous ones...but my forecast below develops this system slowly due to the uncertainty of dry air in addition to the unfavorable TUTT discussed in the atmo outlook section above. As far as sea-surface temperatures...the tropical wave will be tracking over 27 to 28 deg C thru the forecast period which will be on the favorable side for tropical development.

24 Hr Forecast (0000Z August 12)...Tropical low centered near 11N-28W.

48 Hr Forecast (0000Z August 13)...Tropical low centered near 11N-34W.

72 Hr Forecast (0000Z August 14)...35 mph max sustained wind tropical depression centered near 11N-40W.

96 Hr Forecast (0000Z August 15)....45 mph max sustained wind tropical storm centered near 11N-46W.

120 Hr Forecast (0000Z August 16)...50 mph max sustained wind tropical storm centered near 12N-52W.

2014 Atlantic Hurricane Season Birdseye Discussion #59

By: NCHurricane2009, 3:54 AM GMT on August 10, 2014

...SATURDAY AUGUST 9 2014 11:55 PM EDT...
A strong tropical wave over western Africa has become better organized between 1800Z and 0000Z this evening...and is expected to emerge into the eastern tropical Atlantic waters in the next 24 hours. As the atmospheric features chart below shows...upper vorticity marked by blue-dashed lines is located in the central tropical Atlantic...northeastern Atlantic...and northwestern Atlantic. Over the next week...this upper vorticity is forecast to merge into a Tropical Upper Tropospheric Trough (TUTT) that will eventually shift south ahead of an amplifying western Atlantic upper ridge. However if current trends continue...this tropical wave has a high chance of additional development while passing south of the unfavorable TUTT. If the tropical wave continues to become organized...I will consider upgrading it to a special feature in my next blog post.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_09_2014_2215Z_zps79abd60e.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 1949Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_09_2014_2215Z_Thermo_zps1d6b4142.png
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).

2014 Atlantic Hurricane Season Birdseye Discussion #58

By: NCHurricane2009, 11:36 AM GMT on August 09, 2014

...SATURDAY AUGUST 9 2014 7:40 AM EDT...
A rather large and strong tropical wave has become defined over interior western Africa over the last 24 hours...and is expected to emerge into the eastern tropical Atlantic waters in the next 48 hours. As the atmospheric features chart below shows...upper vorticity marked by blue-dashed lines flanks the deep-layered 1029 mb subtropical ridge currently in the Atlantic. This upper vorticity is shown in computer models to persist over the next few days...and therefore development of this tropical wave will depend on whether or not it interacts with the unfavorable upper vorticity.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_08_2014_2345Z_zps75c45a52.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z and the 0118Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_08_2014_2345Z_Thermo_zpsc3f64297.png
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).

2014 Atlantic Hurricane Season Birdseye Discussion #57

By: NCHurricane2009, 8:59 AM GMT on August 08, 2014

...FRIDAY AUGUST 8 2014 5:00 AM EDT...
Atlantic tropics remain quiet.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_07_2014_2345Z_zps0df0a16e.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_07_2014_2345Z_Thermo_zpsd7a779b2.png
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).

2014 Atlantic Hurricane Season Birdseye Discussion #56

By: NCHurricane2009, 9:32 AM GMT on August 07, 2014

...THURSDAY AUGUST 7 2014 5:34 AM EDT...
Bertha has become a non-tropical remnant low accelerating eastward in the northwestern Atlantic. In the wake of Bertha...the Atlantic tropics are quiet.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_06_2014_2345Z_zps53ac2e67.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z and the 0128Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_07_2014_0015Z_Thermo_zps0f28775a.png
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).

2014 Atlantic Hurricane Season Birdseye Discussion #55

By: NCHurricane2009, 3:15 AM GMT on August 06, 2014

...TUESDAY AUGUST 5 2014 11:16 PM EDT...
Bertha has weakened to a tropical storm as she races northeastward into the open northwestern Atlantic...and is expected to transition into a non-tropical remnant low by 36 hours. See special feature section below for additional details on Bertha.

A bulk of the disturbed weather across the Florida peninsula and waters just offshore of the southeastern United States has consolidated into a 1012 mb low pressure center offshore of the Carolinas...but is being swept northeastward in the same steering flow as Bertha in advance of the eastern North America-Gulf of Mexico merged upper trough. This 1012 mb low is expected to become absorbed into the broad low pressure region developing in the northwestern Atlantic that will be a combination of Bertha and the 1009 mb southeastern Canada frontal cyclone marked in the atmospheric features chart below. While the northern portion of the merged upper trough will push offshore from North America...the southern portion will retrograde westward across the Gulf of Mexico...allowing favorable upper ridging currently over Florida to expand into the Gulf of Mexico in its wake. However with most of the disturbed weather collected around the 1012 mb low zooming northeast...their seems to be too little disturbed weather to work with in the eastern Gulf of Mexico that could take advantage of the upper ridging expanding into the Gulf.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_05_2014_2045Z_zps28e0e90a.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 1924Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_05_2014_2045Z_Thermo_zps552ae22d.png
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 BERTHA...
Current prognosis...As of the 11 PM EDT NHC advisory the center of Tropical Storm Bertha was located at 37.5N-68.1W...tracking northeastward and increasingly eastward in the flow due south of the 1009 mb southeastern Canada frontal cyclone (marked in the above atmospheric features chart) that is supported by the eastern divergence of the eastern North America upper trough. Even though the storm is under westerly shear due to the strong upper southwesterly flow in advance of the aforementioned upper trough...Bertha this past afternoon and through this evening continues to intermittently impress by firing off strong storm bursts east of the center that at times covers the center.

Atmospheric Outlook for the Forecast Period...In the short term the track of Bertha will bend on a more eastward direction in the flow on the south side of the 1009 mb southeastern Canada frontal cyclone. The track will then bend more northward around the east side of the frontal cyclone. The 999 mb deep-layered cyclone and upper trough southeast of Greenland in the above atmo chart will slide into the northeast Atlantic during the forecast period...with upper convergence on the west side of the cyclone supporting a north Atlantic surface ridge to the east of Bertha that will also help deflect the track of Bertha more northward (this surface ridge has begun to form with the 1018 mb surface high marked near the east coast of Newfoundland in the above atmo chart). Then at the very end of the forecast period...a non-tropical Bertha will bend more eastward in track while breaking through the north Atlantic surface ridge while becoming pulled into the northeast Atlantic deep-layered cyclone.

Thermodynamic Outlook for the Forecast Period...This system is currently over 27 to 28 deg C waters...and in the next 24 hours this system will be riding east-northeast to northeast along the sharp temperature gradient of the north wall of the Gulf stream. By 36 hours it will have crossed the gradient and into waters below 26 deg C which will encourage Bertha's thunderstorm intensity to die down...which in turn will aid in Bertha's transition to a non-tropical entity.

 photo Aug_5_2014_TS_Bertha_Forecast_zps0735b0d3.png

Track Forecast...Based on Bertha's positioning this evening...she has tracked a little faster and is a little further north than previously thought in my previous forecast from discussion #54. Therefore my updated track forecast above is similar to my previous...but with all points moved a bit rightward and northward to adjust for where Bertha has been tracking this evening. My forecast track line initially shows a bend towards the east-northeast thru 8 PM Wednesday...with a northward deflection thru 8 PM Thursday...and then an eastward deflection at the very end due to the forecast influences discussed in the above atmo outlook section.

Intensity Forecast...Even though Bertha is battling westerly shear...her acceleration to the east-northeast is making the storm track more aligned with the direction and speed of the upper westerlies which overall means a reduction (but not elimination) of storm relative westerly shear. This may allow for the storm bursts mentioned in the current prognosis section to stay near enough the center to maintain current strength for the next 24 hours (which is what my intensity forecast above shows)...especially with the expected storm track allowing exposure to 26+ deg C waters during this timeframe. In fact I would not be suprised if Bertha slightly restrengthens in an impressive storm burst during the next 24 hours. But by 36 hours with arrival to waters below 26 deg C...this should encourage weakening. However I only slightly weaken Bertha at 36 hours as she should be transitioning to a non-tropical low supported by the eastern North America upper trough's eastern divergence.

Impact Forecast...Impact swath in the above forecast graphic is extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track. Sea swells are occuring in the storm vicinity...but are not substantial with the storm's small size and moderate-tropical-storm-force winds.

2014 Atlantic Hurricane Season Birdseye Discussion #54

By: NCHurricane2009, 4:33 AM GMT on August 05, 2014

...TUESDAY AUGUST 5 2014 12:35 AM EDT...
Bertha becomes a hurricane earlier than expected while moving northward in the western Atlantic. Additional strengthening is not expected...and Bertha is expected to weaken for the remainder of its lifespan while encountering less favorable atmospheric and thermodynamic conditions while curving on a more norheastward track across the northwestern Atlantic. See special feature section below for additional details on Bertha.

Disturbed weather continues across the Florida peninsula and waters just offshore of the southeastern United States associated with a suface trough over Florida and a coastal frontal boundary supported by divergence on the east side of the eastern North America upper trough. A western Caribbean cut-off upper vortex has retrograded into the southern Gulf of Mexico as an inverted upper trough and is merging with the eastern North America upper trough. Over the next 48 hours the northern portion of the merged upper trough will push offshore from North America...taking much of the disturbed weather northeastward with it. However the southern portion of the merged upper trough will retrograde westward across the Gulf of Mexico...allowing favorable upper ridging currently over the Florida surface trough to expand into the Gulf of Mexico in its wake. Therefore watching to see if the Florida surface trough leaves behind a fragment in the eastern Gulf of Mexico over the next 48 hours which could then become a disturbance if it takes advantage of the upper ridging expanding into the Gulf.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_04_2014_2245Z_zps21c54ffa.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and the 1906Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_04_2014_2245Z_Thermo_zps43dbc8b9.png
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...HURRICANE BERTHA...
Current prognosis...As of the 11 PM EDT NHC advisory the center of Hurricane Bertha was located at 31.3N-73.1W...tracking north-northeastward well offshore of the eastern US coast and well west of Bermuda. Even though reconnaissance aicraft measurements earlier this afternoon showed a category 1 hurricane of 75 to 80 mph max sustained winds...Bertha has never looked like a conventional hurricane with the lack of a central eye and blobbed thunderstorm activity continuing to be biased to the southeast side of the circulation while continuing to deal with westerly vertical shear imparted by the upper outflow of the Florida surface trough disturbance. The satellite presentation of Bertha has detereorated under the shear since this afternoon while the center has become an exposed cloud swirl seperated from the thundestorm activity. However the National Hurricane Center chose to keep Bertha a hurricane as of the recent 11 PM EDT advisory...waiting for the next reconnaissance aircraft observations to confirm that Bertha has weakened below hurricane strength because Bertha has been measuring stronger than what satellite presentations suggest.

Atmospheric Outlook for the Forecast Period...This system will be taking an arcing track around the northwest side of what is now the 1025 mb Atlantic surface subtropical ridge marked in the above atmospheric features chart. The eastern North America upper trough (marked by blue dashed line in the above atmo chart) is producing a 1013 mb frontal depression over southeastern Canada which will soon strengthen to a frontal cyclone...with Bertha curving east-northeast between the north side of the surface Atlantic subtropical ridge and south side of the frontal cyclone. The track will then bend more northward around the east side of the frontal cyclone. The 993 mb deep-layered cyclone and upper trough southeast of Greenland in the above atmo chart will slide into the northeast Atlantic during the forecast period...with upper convergence on the west side of the cyclone supporting a north Atlantic surface ridge to the east of Bertha that could also help deflect the track of Bertha more northward (this surface ridge has begun to form with the 1018 mb surface high marked on the east coast of Canada in the above atmo chart). Then at the very end of the forecast period...a non-tropical Bertha will bend more eastward in track while breaking through the north Atlantic surface ridge while becoming pulled into the northeast Atlantic deep-layered cyclone.

Thermodynamic Outlook for the Forecast Period...This system is currently over 29 deg C waters...but by 36 hours this system will cross the sharp temperature gradient of the north wall of the Gulf stream and into waters below 26 deg C. This will encourage the weakening of this system as a tropical entity beyond 36 hours.

 photo Aug_4_2014_TS_Bertha_Forecast_zps4cd2e0a4.png

Track Forecast...Based on Bertha's positioning this evening...she has tracked a little slower than previously thought in my previous forecast from discussion #53. Therefore my updated track forecast above pretty much follows the track forecast line I presented previously...but I have moved the 8 PM Tuesday and 8 PM Wednesday points a bit further back along that line to adjust for the observation of a slower-than-previously thought track. For the late part of the forecast period...models have shifted more northward toward Newfoundland. I think this is a reflection of the slower-than-previously thought track which will now allow Bertha's circulation to now be closer to the eastern North America upper trough when that upper trough begins to move offshore...which will in turn allow Bertha's circulation to pull down more colder air associated with the upper trough than previously thought. In turn this will allow for a slightly-more-amplified upper trough that bends Bertha's track a bit more northward as she becomes non-tropical. Therefore I have also adjusted my 8 PM Thursday position to be a bit more northward...but have not made this adjustment as far to the north as the models have because my intensity forecast discussed below predicts Bertha to be weaker than previously thought by the time she interacts with the upper trough such that I don't think the upper trough will become as amplified as in some of the latest model runs. My forecast track line initially shows a bend towards the east-northeast thru 8 PM Wednesday...with a bend back towards the north thru 8 PM Thursday...and then a bend back to the east-northeast at the very end due to the forecast influences discussed in the above atmo outlook section.

Intensity Forecast...Even though Bertha has become a hurricane earlier than expected...my updated intensity forecast shown above is below the National Hurricane Center's most recent forecast and below my previous intensity forecast. This is because Bertha currenlty looks dishevled from stronger than expected westerly shear imparted by the upper outflow of the Florida surface trough disturbance to the west has been more impressive than previously thought. My updated intensity forecast predicts continual weakening as Bertha tracks toward cooler waters and should continue to be under westerly shear...at first from the continued outflow of the disturbance to the west...followed by strong southwesterly upper winds ahead of the eastern North America upper trough soon to move offshore. At first I make the weakening rate more rapid...followed by a flattened weakening rate as Bertha gains the support of the upper trough's eastern divergence as a non-tropical entity.

Impact Forecast...Impact swath in the above forecast graphic is extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track...with the swath width narrowed toward the later part of the forecast to reflect the forecast weakening. Even though the impact swath continues to exclude Newfoundland...this could change if the forecast track becomes adjusted further to the north once again. Sea swells are occuring in the storm vicinity...but should diminish with time if Bertha weakens as forecast above.

2014 Atlantic Hurricane Season Birdseye Discussion #53

By: NCHurricane2009, 6:57 PM GMT on August 03, 2014

...SUNDAY AUGUST 3 2014 3:05 PM EDT...
Tropical Storm Bertha is moving across the eastern Bahamas...and is expected to turn north and then northeast across the open northwestern Atlantic over the next few days while intensifying into a strong tropical storm or possibly a category 1 hurricane. Visit www.nhc.noaa.gov for the lastest watches and warnings with this system. See special feature section below for additional details on Bertha.

A surface trough formed over the western Bahamas yesterday with the support of split flow upper divergence between a Tropical Upper Tropospheric Trough (TUTT) upper vortex to the east and western Caribbean TUTT upper vortex to the southwest. The surface trough has moved westward into the Florida peninsula...but is producing a thunderstorm flare up just offshore of southeastern Florida in a favorable low shear-enhanced outflow environment beneath a small upper anticyclone that has developed between the two weakening TUTT upper vortices. Even though radar imagery is showing some rotation in the showers and thunderstorms offshore of southeastern Florida...the rotation is not showing signs of consolidation. Therefore it is currently assumed that this system is not developing fast enough to become a tropical cyclone before becoming assimlated in the next 48 hours into the approaching low pressure field of Tropical Storm Bertha to the east and frontal boundary to the north.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_03_2014_1445Z_zpse89c8d3f.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z and the 1317Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_03_2014_1445Z_Thermo_zpse16d7e0f.png
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 BERTHA...
Current prognosis...As of the 2 PM EDT NHC advisory the center of Tropical Storm Bertha was located at 22.7N-72.6W...beginning to exit the eastern Bahamas and into the open western Atlantic while bending on an increasingly northward track. The thunderstorm activity of Bertha remains biased to the east side of the circulation center as this system continues to deal with westerly vertical shear imparted by the weakening upper vorticity associated with the Tropical Upper Tropospheric Trough (TUTT) mentioned in the atmo outlook section below...and also imparted by the upper anticyclone of the disturbance offshore of southeastern Florida. Ever since leaving the Dominican Repbulic early this morning...satellite imagery suggests this system is a bit better organized with the thunderstorm activity looking less blobbed and a bit more banded.

Atmospheric Outlook for the Forecast Period...This system will be taking an arcing track around the west side of what is now the 1024 to 1027 mb Atlantic surface subtropical ridge marked in the above atmospheric features chart. By connecting the western Caribbean blue L...central Atlantic blue L...and blue dashed lines north and south of Bertha in the above chart...a Tropical Upper Tropospheric Trough (TUTT) that is breaking apart spans the Caribbean to the central Atlantic. In the next 24 hours as the weakening TUTT upper troughs (blue dashed lines) north and south of Bertha dissipate...Bertha will find herself in a more favorable environment below a shear-reducing and outflow enhancing upper ridge (currently this upper ridge is present as marked by a blue H offshore of the eastern US). Towards the end of the forecast period...the eastern North America upper trough (marked by blue dashed line in the above atmo chart) will produce a surface frontal cyclone over southeastern Canada...with Bertha curving east-northeast between the north side of the surface Atlantic subtropical ridge and south side of the frontal cyclone. The track will then bend more northward around the east side of the frontal cyclone. The 990 mb frontal cyclone and upper trough southeast of Greenland in the above atmo chart is expected to evolve into a deep-layered cyclone in the northeast Atlantic during the forecast period...with upper convergence on the west side of the cyclone supporting a north Atlantic surface ridge to the east of Bertha that could also help deflect the track of Bertha more northward. Then at the very end of the forecast period...a non-tropical Bertha will bend more eastward in track while breaking through the north Atlantic surface ridge while becoming pulled into the northeast Atlantic deep-layered cyclone.

Thermodynamic Outlook for the Forecast Period...This system will track over 29 to 30 deg C water early in the forecast period. By 72 hours...if this system follows the forecast track shown below...this system will cross the sharp temperature gradient of the north wall of the Gulf stream and into waters below 26 deg C. This will encourage the weakening of this system as a tropical entity beyond 72 hours.

 photo Aug_3_2014_TS_Bertha_Forecast_zps6b6d3594.png

Track Forecast...Bertha is tracking very well with my previous track forecast shown in discussion #52. Moreover the NHC track forecast in the last 24 hours has become aligned closer to my previous...and therefore my updated forecast track below is a copy-paste of my previous with the exception of the 8 AM Thursday position which is further east. This is because computer models late in the forecast period now suggest Bertha's vigorous circulation will pull down some of the cool air associated with the eastern North America upper trough...which will form a shortwave upper trough and produce a tighter upper-level pressure gradient between the forecast shortwave and upper ridging to the south. A stronger upper-level pressure gradient will cause stronger upper-level winds that will push Bertha on a faster track as she becomes non-tropical...which is why I moved my forecast point for 8 AM Thursday further east. My forecast track line towards the end of the forecast is east-northeast...with a bend towards the north...and then a bend back to the east-northeast at the very end due to the forecast influences mentioned at the end of the above atmo outlook section.

Intensity Forecast...Because Bertha did not degenerate into a tropical wave...I have now bumped up my intensity forecast close to the NHC's most recent which suggests Bertha will breifly become a category 1 hurricane. I keep the intensification very slow for the next 24 hours as Bertha will have to deal with some westerly shear from the upper anticyclone of the tropical disturbance currently offshore of southeastern Florida. I then show more rapid strengthening as the disturbance is expected to have dissipated while becoming absorbed into the west side of Bertha's low pressure field and frontal boundary associated with the eastern North America upper trough. I forecast Bertha to become a hurricane a little earlier than when the latest NHC forecast shows...because I expect Bertha to begin weakening by 8 AM Wednesday while she crosses into cooler waters and begins to deal with westerly vertical shear on the north side of the upper ridge. However the weakening will be on the more gradual side as Bertha becomes a non-tropical cyclone supported by upper divergence on the east side of a forecast shortwave upper trough mentioned in the above track forecast section.

Impact Forecast...Impact swath in the above forecast graphic is extrapolation of the 11 AM EDT NHC tropical storm wind radius along my forecast track. Flooding from rainfall should not be an issue in the eastern Bahamas since the storm field of Bertha is relatively small and weak and since Bertha should remain on a brisk track...although isolated flash flooding can't be ruled out from a heavy shower. Sea swells early in the forecast period should not be much of an issue as Bertha is expected to be weak...but become more of a concern in the storm vicinity later in the forecast period if Bertha strengthens as forecast in the western Atlantic.

2014 Atlantic Hurricane Season Birdseye Discussion #52

By: NCHurricane2009, 6:02 PM GMT on August 02, 2014

...SATURDAY AUGUST 2 2014 2:03 PM EDT...
Tropical Storm Bertha has crossed the Lesser Antilles with gusty winds and rainfall in the last 24 hours...and is currently striking Puerto Rico while the center is located just south of the island. Bertha is headed for landfall in the Dominican Repbulic later today and is likely to affect the eastern Bahamas tomorrow. Visit www.nhc.noaa.gov for the lastest watches and warnings with this system. See special feature section below for additional details on Bertha.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Aug_02_2014_1145Z_zpsfebf0799.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z and the 1311Z-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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Aug_02_2014_1145Z_Thermo_zps6cdf22f9.png
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 BERTHA...
Current prognosis...The center of Tropical Storm Bertha was located at 17.2N-66.7W...or just south of Puerto Rico...and continuing to move west-northwest at a brisk pace as of the 11 AM EDT National Hurricane Center advisory. The thunderstorm activity of Bertha remains biased to the east side of the circulation center as this system continues to deal with westerly vertical shear imparted by upper vorticity associated with the Tropical Upper Tropospheric Trough (TUTT) mentioned in the atmo outlook section below. Radar and satellite presentations show that the circulation of Bertha is currently loosely defined almost to suggest that Bertha later tonight could open into a tropical wave while becoming disrupted by the mountainous terrain of the Dominican Republic.

Atmospheric Outlook for the Forecast Period...This system will be taking an arcing track around the west side of what is now the 1029 mb Atlantic surface subtropical ridge marked in the above atmospheric features chart. By connecting the series of blue Ls from the Caribbean to central Atlantic in the above chart...a Tropical Upper Tropospheric Trough (TUTT) spans the Caribbean to the central Atlantic. Early in the forecast period...Bertha will continue to battle the unfavorable TUTT. The TUTT is already breaking down in the vicinity of Bertha as the TUTT's upper vorticity is splitting apart to the north and south of the tropical storm as shown by the blue Ls north and south of Bertha in the above chart. After the TUTT breaks down and Bertha recurves into the western Atlantic...Bertha will find herself in a more favorable environemnt below a shear-reducing and outflow enhancing upper ridge (currently this upper ridge is present as marked by a blue H offshore of the eastern US). Towards the end of the forecast period...models generally agree that the eastern North America upper trough (marked by blue dashed line in the above atmo chart) will produce a surface frontal cyclone over southeastern Canada...with Bertha curving east-northeast between the north side of the surface Atlantic subtropical ridge and south side of the frontal cyclone. The track at the very end of the forecast period could bend more northward around the east side of the frontal cyclone. The 1002 mb frontal cyclone and upper trough over southern Greenland in the above atmo chart is expected to evolve into a deep-layered cyclone in the northeast Atlantic during the forecast period...with upper convergence on the west side of the cyclone supporting a north Atlantic surface ridge to the east of Bertha that could also help deflect the track of Bertha more northward at the end of the forecast period.

Thermodynamic Outlook for the Forecast Period...This system will track over 29 to 30 deg C water early in the forecast period. By 96 hours...if this system follows the forecast track shown below...this system will cross the sharp temperature gradient of the north wall of the Gulf stream and into waters below 26 deg C. This will encourage the weakening of this system as a tropical entity beyond 96 hours.

 photo Aug_2_2014_TS_Bertha_Forecast_zps5498eb3d.png

Track Forecast...The 11 AM EDT position of Bertha is approximately the 2 PM EDT position put out in the previous forecast in discussion #51. Therefore my updated forecast track above is a bit faster-paced than my previous...which makes my updated track a bit faster than the NHC's early in the forecast period. Because Bertha is also tracking a bit more west and a bit less north than previously forecast...and because Bertha could open into a tropical wave tonight when it interacts with the Dominican Republic mountanious terrain...my updated forecast track is also left of the NHC's early on as a tropical wave tends to track more west and less north compared to a closed circulation. Because my early forecast track has a larger radius compared to NHC's slower track...later in the forecast my track ends up re-aligning with the NHC's. My forecast track line towards the end of the forecast is east-northeast with a bend towards the north due to the forecast influences mentioned at the end of the above atmo outlook section.

Intensity Forecast...I am just below the 11 AM EDT NHC intensity forecast as I predict that Bertha will open into a tropical wave later today due to westerly shear and land interaction with the Dominican Repbulic. However I forecast that Bertha will re-generate into a tropical storm by Monday while sliding under the shear reducing and outflow enhancing upper ridge mentioned in the above atmo outlook section. I am reluctant to suggest Bertha becoming a hurricane by 96 hours like the NHC 11 AM forecast showed in case Bertha never regenerates into a tropical cyclone...and because by that time Bertha will be crossing into cooler waters and be under some westerly vertical shear on the north side of the upper ridge.

Impact Forecast...Impact swath in the above forecast graphic is extrapolation of the 11 AM EDT NHC tropical storm wind radius along my forecast track...with a little expansion of the swath width toward the end of the forecast with the anticipation that Bertha could strengthen in the western Atlantic. Flooding from rainfall should not be an issue since the storm cluster of Bertha is relatively small and since Bertha should remain on a brisk track...although isolated flash flooding in Puerto Rico...the Dominican Republic...and eastern Bahamas can't be ruled out from a heavy shower. However the rainfall from Bertha will be welcome as many of the islands in the region have been dealing with drought. Sea swells early in the forecast period should not be much of an issue as Bertha is expected to remain weak...but become more of a concern in the storm vicinity later in the forecast period if Bertha strengthens in the western Atlantic.

2014 Atlantic Hurricane Season Birdseye Discussion #51

By: NCHurricane2009, 11:14 AM GMT on August 01, 2014

...FRIDAY AUGUST 1 2014 7:15 AM EDT...
After once again losing thunderstorm activity yesterday afternoon due to dry air...the circulation of tropical disturbance Invest 93-L approaching the Lesser Antilles has redeveloped an increase in thunderstorms overnight. Coupled with yesterday afternoon's aircraft reconnaissance observations of tropcal storm force winds...this system has been upgraded to Tropical Storm Bertha. Watches and warnings are in effect for the Lesser Antilles...Puerto Rico...and the Virgin Islands. Visit www.nhc.noaa.gov for the lastest information on watches and warnings. See special feature section below for additional details on Bertha.

The tropical wave southwest of the Cape Verde Islands has become less organized in the past 24 hours in an environment of southeasterly shear on the east side on an inverted upper trough. And because computer models continue to insist this tropical wave will not develop...I have now dropped this tropical wave as a special feature on this blog.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...
 photo Jul_31_2014_2045Z_zpsb77db1a2.png
This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z last evening.

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. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...
 photo Jul_31_2014_2045Z_Thermo_zps6c82971b.png
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 BERTHA...
Current prognosis...The center of Tropical Storm Bertha was located at 13N-57W and moving west-northwest at a brisk pace as of the 5 AM EDT National Hurricane Center advisory. By comparing the earlier 11 PM advisory to where this system was centered at 11 PM July 29 (during discussion #49)...this system has been making a 1.5N to 2N latitude and 7W longitude progression per 24 hours. The thunderstorm activity of Bertha is becoming biased to the east side of the circulation center as this system begins to deal with westerly vertical shear imparted by an upper vortex to the northwest (marked by blue L in the above atmospheric features chart). This upper vortex is part of the Tropical Upper Tropospheric Trough (TUTT) mentioned in the atmo outlook section below.

Atmospheric Outlook for the Forecast Period...This system will be taking an arcing track around the west side of what is now the 1029 mb Atlantic surface subtropical ridge marked in the above atmospheric features chart. By connecting the series of blue-dashed lines and blue Ls from the Caribbean to northeast Atlantic in the above chart...a Tropical Upper Tropospheric Trough (TUTT) spans the Caribbean to the northeast Atlantic. And by connecting the the series of blue Hs and blue zig-zag lines in the above chart...a lengthy upper ridge extends from northern Mexico...northern Gulf of Mexico...and across the north Atlantic. Early in the forecast period...Bertha will have to battle with the unfavorable upper vortex to the northwest...which will drop south into the central Caribbean/Bahamas region and weaken into an inverted upper trough as the TUTT breaks down. After the TUTT breaks down and Bertha recurves into the western Atlantic...Bertha will find herself in a more favorable environemnt below the aformentioned upper ridge. At the very end of the forecast period...models generally agree that the eastern North America upper trough (marked by blue dashed line in the above atmo chart) will produce a surface frontal cyclone over southeastern Canada...with Bertha likely to travel east-northeast between the north side of the surface Atlantic subtropical ridge and south side of the frontal cyclone.

Thermodynamic Outlook for the Forecast Period...This circulation has traveled westward into increasingly warmer waters of 29 deg C...which may have provided enough instability for this system to suddenly fire off the thunderstorm cluster now present on its east side and quickly become Tropical Storm Bertha overnight in the face of dry air. With the forecast track below taking this system over more 29 deg C waters and into the more moist western Atlantic environment shown in the above thermodynamics chart...the thermodynamic parameters for Bertha should remain on the favorable side thru the forecast period.

 photo Aug_1_2014_TS_Bertha_Forecast_zpsbff442be.png

Track Forecast...By extrapolating the 24-hourly forward motion of 7W and 1.5N to 2N per 24 hours noted in the above current prognosis section...the NHC forecast track above for the next 24 hours is in good agreement with current observations of forward pace. Moreover...the NHC forecast track generally follows the shape of the west side of the surface subtropical ridge depicited in computer model runs...and therefore for the most part my forecast track above is in agreement with the NHC's. At the very end of the forecast period...the NHC's forecast track seems to suggest a more northeast motion...but I prefer a more east-northeast motion as Bertha should be situated on the north side of the aforementioned surface subtropical rideg and south side of a forecast frontal cyclone over southeast Canada.

Intensity Forecast...I am below the 5 AM EDT NHC intensity forecast early in the forecast period as I predict some weakening from the westerly shear on the east side of the TUTT upper vortex mentioned in the above atmo outlook section. Land interaction with Puerto Rico and the eastern tip of the Dominican Repbulic may also cause problems for Bertha early in the forecast. If Bertha survives the shear and land interaction...then her potential for development in the western Atlantic looks good while sliding under the shear reducing and outflow enhancing upper ridge mentioned in the above atmo outlook section...and therefore my forecast intensity later in the forecast period becomes above the 5 AM EDT NHC intensity forecast.

Impact Forecast...Impact swath in the above forecast graphic is extrapolation of the 5 AM EDT NHC tropical storm wind radius along my forecast track...with a little expansion of the swath width toward the end of the forecast with the anticipation that Bertha could strengthen in the western Atlantic. Flooding from rainfall should not be an issue since the storm cluster of Bertha is relatively small and since Bertha should remain on a brisk track...although isolated flash flooding in the Lesser Antilles...Virgin Islands...Puerto Rico...or eastern Dominican Republic can't be ruled out from a heavy shower. However the rainfall from Bertha will be welcome as many of the islands in the region have been dealing with drought. Sea swells early in the forecast period should not be much of an issue as Bertha is expected to remain weak...but become more of a concern in the storm vicinity later in the forecast period if Bertha strengthens in the western Atlantic.


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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