NCHurricane2009's Blog

2015 Atlantic Hurricane Season Birdseye Discussion #73

By: NCHurricane2009, 4:25 AM GMT on August 31, 2015

...MONDAY AUGUST 31 2015 12:25 AM EDT...
Special statement: I have graciously learned on Dr. Masters blog this past afternoon that a decision was made at the United Nations in late October of 2013 that the Cape Verde Islands are to be referred to as the Republic of Cabo Verde. Henceforth on this blog I will be referring to the Cape Verde Islands as the Republic of Cabo verde.

Rapidly developing Tropical Storm Fred likely to make history in the Republic of Cabo Verde...expected to become the first tropical cyclone to strike the Republic as a category 1 hurricane by tomorrow morning. A hurricane warning continues to be in effect for the Republic and all preparations should have been rushed to completion by now. Continue to visit www.nhc.noaa.gov for up to the minute latest information on Fred...including information on warnings in effect for the Republic of Cabo Verde. After clearing the islands of the Republic...Fred is expected to weaken into a mid-ocean remnant low later this week. See Fred special feature section below for more details.

After producing very heavy thunderstorms over south Florida and western Cuba last night...the remnant surface trough of former Tropical Storm Erika appears to be weakening in the eastern Gulf of Mexico tonight while featuring much weaker activity. Therefore Erika is no longer expected to regenerate into a tropical cyclone and I have cancelled it as a special feature on this blog.

An upper vortex has ejected northeastward from the western Gulf of Mexico and into the southeastern United States over the last 36 hours...and has merged with a shortwave upper trough that was moving across the central US...resulting in a vigorous shortwave upper trough marked as a blue-dashed line over the eastern US in the atmospheric features chart below. Divergence on the east side of the shortwave has expanded the surface trough of the remnant of Erika...as well as showers and thunderstorms...northward from Florida and into the Carolinas as well as the waters offshore of the Carolinas. The shortwave upper trough is expected to merge with the 1003 mb frontal depression and its shortwave currently over eastern Canada as the 1003 mb frontal depression moves away into the north-central Atlantic during the next 48 hours...leaving favorable upper winds offshore of the southeastern United States as the western Atlantic upper ridge (marked by blue H between the Carolinas and Bermuda in the atmospheric features chart below) expands in its place. Therefore it remains to be seen if tropical activity offshore of the Carolinas develops along the surface trough. So far there are no signs of this occuring...and none of the major computer models currently forecast this to occur.

The frontal cyclone that has moved into southern Greenland has left behind a decaying cold front over the western Atlantic. A 1018 mb surface low along the decaying front located just northwest of Bermuda fired some vigorous thunderstorms this past afternoon which have weakened this evening. As the 1003 mb frontal depression over eastern Canada intensifies into a frontal cyclone while moving into the north-central Atlantic...the 1018 mb surface low is expected to accelerate eastward in westerly flow on the south side of the frontal cyclone and become absorbed by the cold front of the frontal cyclone by 48 hours. The 1018 mb surface low is not expected to develop into a tropical cyclone before its absorption as unfavorable westerly vertical shear increases on the south side of the amplifying upper trough associated with the frontal cyclone.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL STORM FRED...
Current Prognosis...Fred is a classic healthy tropical cyclone in a low shear vertical shear and enhanced upper outflow environment tonight...featuring a central dense overcast of thunderstorms with spiral bands wrapped around. Maximum sustained winds near the center are estimated at 70 mph as of the 11 PM EDT advisory from the NHC...which means Fred is just below hurricane force. As of 0000Z earlier this evening Fred was centered at 14.9N-21.8W and is about to move northwestward into the Republic of Cabo Verde. As such...severe weather (heavy rain and damaging winds) will be moving into the Republic through tomorrow morning and afternoon.

Atmospheric Outlook for the Forecast Period...The surface subtropical ridge in the eastern Atlantic is re-organizing further north around what is currently the 1025 mb center north of the Azores supported by upper convergence on the back side of the eastern Atlantic upper trough (marked by blue-dashed line on the upper right side of the above atmopsheric features chart). This northward re-location of the surface ridge...coupled with the fact Fred has quickly become strong/tall enough to be steered by a cut-off upper vortex left behind by the upper trough (marked by blue L adjacent to Fred)...has caused Fred to accelerate northwestward toward the Republic of Cabo Verde faster than expected. Because Fred is now left of previous forecast tracks...he will now interact with a ridge weakness associated with a strong frontal cyclone and associated upper vortex that will enter the north-central Atlantic from eastern Canada (the early phase of this frontal cyclone can be seen in the top-left of the above atmospheric features chart...with the 1003 mb frontal depression and its associated shortwave upper trough coming into view over eastern Canada). It is not until 72 hours that the track of Fred will bend more westward as the weakness fills in when the frontal cyclone and its upper vortex lifts out to the north. After 24 hours...Fred will run into unfavorable southwesterly vertical shear induced by the aforementioned adjacent cut-off upper vortex. Even though the upper vortex is still forecast to weaken...the GFS model has been more aggressive with maintaining the TUTT (Tropical Upper Tropospheric Trough) currently marked by a blue-dashed line northeast of the Lesser Antilles...and has been showing that the TUTT will be at a further south location than previously thought. Coupled with the northward adjusted later part of the forecast track...it seems a sure bet that Fred will now run into the TUTT and get sheared apart by the TUTT.

Thermodynamic Outlook for the Forecast Period...Fred will stay over favorable waters above 26 deg C thru the forecast period. However thermodynamic parameters are not expected to be favorable for Fred due to the dry saharan air layer (SAL). The above thermodynamics chart and SAL analysis from CIMSS suggest that strengthening northeasterly winds ahead of Fred....caused by the pressure gradient between Fred's strengthening circulation and the surrounding environment...have driven a large slug of SAL southwestward in the environment ahead of Fred. Therefore...expect this unfavorable SAL to get driven into Fred by increasing westerly shear after 24 hours.


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

12 Hr Forecast (1200Z Aug 31)...85 mph maximum sustained wind hurricane centered over the northeastern part of the Republic of Cabo Verde...at 16.2N-24W

24 Hr Forecast (0000Z Sep 1)...80 mph maximum sustained hurricane centered just northwest of the Repbulic of Cabo Verde...at 17.5N-26W

48 Hr Forecast (0000Z Sep 2)...60 mph maximum sustained wind tropical storm centered at 20N-30W

72 Hr Forecast (0000Z Sep 3)...40 mph maximum sustained wind tropical storm centered at 21.5N-34.5W

96 Hr Forecast (0000Z Sep 4)...Remnant low centered at 23N-39W

Track Forecast...The big change with the track forecast is due to a faster northwest track in the short-term (due to the rapid initial motion noted in the current prognosis)...which causes Fred to continue northwest in the middle part of the forecast track as he will now reach the ridge weakness associated with the forecast north-central Atlantic frontal cyclone mentioned in the above atmo outlook section. Fred is still expected to bend more westward in track by the end of the forecast period as the frontal cyclone lifts out to the north...but with a northward adjusted middle part of the forecast track the later part of the forecast track is also adjusted northward.

Intensity Forecast...The short-term intensity forecast is raised due to the rapid strengthening Fred has undergone over the last 24 hours. The long term intensity forecast is lower than my previous due to a higher chance of wind shear and dry air killing the storm as noted in the above atmo and thermo outlook sections. In fact I dissipate Fred into a remnant low by 96 hours.

Impact Forecast...Impact swath in the above graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track. I have added impact statement (b) in the above forecast graphic because Fred is now a strong...moisture rich tropical cyclone capable of dumping heavy rains on the arid soils of the Republic of Cabo Verde.

2015 Atlantic Hurricane Season Birdseye Discussion #72B (Special Update)

By: NCHurricane2009, 7:07 PM GMT on August 30, 2015

...SUNDAY AUGUST 30 2015 3:07 PM EDT...
Because of the immediate threat to the Cape Verde Islands...the following special update is to note changes in track and intensity in Tropical Storm Fred located in the far eastern tropical Atlantic since special update #72A.

Visible satellite imagery showed Tropical Storm Fred developing a banding-type eye feature late this morning and early this afternoon...with the most recent visible satellite frame showing a hot tower burst covering the eye. Moreover the impressive core of Fred is surrounded by very well organized sprial bands. Previous thinking was that the dry Saharan air layer near the Cape Verde Islands could limit the strengthening of the storm...but because the low vertical shear has allowed Fred to keep his thunderstorm vertically aligned with the center...the latest CIMSS Saharan Air Layer (SAL) analysis shows that Fred's moisture field has plowed away the dry air in the vicinity of the Cape Verde Islands. Therefore the short-term intensity forecasts have been increasing and Fred is expected to strike the Cape Verde Islands at least as a category 1 hurricane (possibly stronger). A hurricane warning was issued for the Cape Verde Islands earlier today. Fred has been tracking to the left of my 1 AM EDT forecast shown in special update #72A and to the right of the 1 AM EDT NHC forecast also shown in update #72A...and therefore conditions will go downhill in the Cape Verde Islands tomorrow morning and afternoon. Preperations in the Cape Verde Islands for a signficant hurricane should be rushed to completion.

CIMSS SAL (Saharan air layer) analysis...as well as all water vapor satellite imagery...also show that northeasterly winds driven by the pressure gradient between Fred's strengthening circulation and the surrounding environment have driven a mass of Saharan dry air southwestward along the future track of Fred. Furthermore each successive run of the GFS computer model shows more westerly vertical shear along the future track of Fred. Therefore I will be lowering my longer-term intensity forecast on Fred...showing Fred weakening after it passes the Cape Verde Islands as the westerly shear pushes aside Fred's thunderstorms and drives the dry air into the circulation.

My next full blog update on the Atlantic tropics...including an update on the remnants of Erika moving into the Gulf of Mexico...will come out late tonight. In the meantime continue referring to www.nhc.noaa.gov for up to the minute latest information on Fred...which includes the latest information on warnings that are in effect for the Cape Verde Islands.

2015 Atlantic Hurricane Season Birdseye Discussion #72A (Special Update)

By: NCHurricane2009, 6:40 AM GMT on August 30, 2015

...SUNDAY AUGUST 30 2015 2:40 AM EDT...
Tropical low Invest 99-L just offshore of western Africa has been upgraded to the sixth tropical depression of the 2015 Atlantic Hurricane Season. A tropical storm warning and hurricane watch have been raised for the Cape Verde Islands. Visit www.nhc.noaa.gov for up to the minute lastest information on this tropical cyclone including the latest on the watches and warnings for the Cape Verde Islands. It is very likely that tropical depression six will strengthen to Tropical Storm Fred later today.

See Invest 99-L special feature section of full discussion #72 for my prognosis and forecast reasoning for newly-formed tropical depression six. Below I have overlaid my tropical depression six forecast on top of National Hurricane Center (NHC) 1 AM EDT forecast graphic. My intensity forecast is below the NHC's 1 AM EDT forecast...but both intensity forecasts keep this system below hurricane force as this system will move northward toward the more stable dry Saharan air layer. However like we saw with Danny last week...there is a possiblity that the low vertical shear allows the thunderstorm core to stay vertically aligned with the surface center and prevent the dry air from penetrating the center...in which case this system could in fact strengthen into a hurricane. This is why a hurricane watch is in effect for the Cape Verde Islands.

Return to full discussion #72 for an assessment on the rest of the Atlantic tropics...including an update on the remnant of Erika.

2015 Atlantic Hurricane Season Birdseye Discussion #72

By: NCHurricane2009, 5:05 AM GMT on August 30, 2015

...SUNDAY AUGUST 30 2015 1:05 AM EDT...
Tropical Storm Erika becomes a poorly-organized remnant low that has rapidly moved northwestward from Haiti to the waters just north of Cuba and just south of the Florida peninsula in only 24 hours. Erika has moved past the TUTT (Tropical Upper Tropopsheric Trough) fragment that sheared it apart...and the unfavorable upper vortex ejecting northeastward from the western Gulf of Mexico cut-off upper trough will soon move away which could allow upper winds in the eastern Gulf of Mexico to become more favorable for Erika to regenerate. If Erika re-generates...she could transition into a slow moving tropical or subtropical-like cyclone supported by upper divergence on the east side of the western Gulf cut-off upper trough capable of soaking the southeastern United States in the Florida panhandle/Alabama region...perhaps creating a flooding risk. See Erika special feature section below for more details.

Elsewhere...the vigorous tropical wave just offshore of Africa has rapidly organized into tropical low Invest 99-L. It should be noted that 99-L has potential to move into the Cape Verde Islands as a tropical cyclone by 48 to 72 hours...and therefore interests in these islands should continue to monitor 99-L. See second special feature section below for an update on 99-L.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...REMNANT OF ERIKA (INVEST 90-L)...
Current Prognosis...Erika this morning lost the battle against land interaction with Haiti and westerly wind shear generated by what is left of a weakening TUTT (Tropical Upper Tropospheric Trough) in the area (marked by a blue-dashed line in the central Caribbean Sea in the atmospheric features chart above). This has resulted in Erika de-generating into a poorly-organized surface low/trough as it moved across eastern Cuba today. It should be noted that the spin seen over eastern Cuba is not the remnant of Erika...but instead is the aforementioned weakening TUTT. Instead...visible satellite animation showed that the remnant surface/low trough of Erika was centered just offshore of the north Cuban coast at approximately 23N-79W as of 0000Z. This is north and west of my previous forecast track and therefore I have once again adjusted my forecast track below accordingly. The thunderstorm activity currently over Florida is not associated with Erika...but instead is produced by upper divergence on the east side of an upper vortex ejecting northeastward from the western Gulf of Mexico cut-off upper trough. This upper vortex will soon move northeastward and away while merging with the central US 1015 mb frontal depression and its associated shortwave upper trough. Meanwhile this shortwave upper trough extends into Texas...and the Texan part of the shortwave will re-enforce the western Gulf of Mexico cut-off upper trough.

Atmospheric Outlook for the Forecast Period...Erika has finally tracked increasingly to the north in response to a low-level ridge weakness created by upper-level divergence on the east side of the cut-off upper trough in the western Gulf of Mexico. The reason the current track is northwest instead of purely north is because of the 1023 mb surface ridge over the eastern United States supported by upper convergence on the west side of upper trough associated with the 1001 mb frontal cyclone near southern Greenland. It is not until the end of the forecast period that Erika is expected to bend completely northward in track as Erika comes under the influence of the western Gulf cut-off upper trough. I show a very slow northeastward track into the Gulf coast at the Florida/Alabama border as the cut-off upper trough tries to push Erika into the southeastern US while the 1023 mb eastern US surface ridge (which will be quasi-stationary thru the forecast period) blocks this motion. If my forecast below turns out to be correct...there is a possibility Erika transitions into a more subtropical-type of cyclone supported by upper divergence on the east side of the cut-off upper trough with the slow northeastward motion perhaps creating a prolonged rainfall period with a flooding risk in the Florida panhandle/southern Alabama region of the southeastern US. I show a conservative intensity forecast due to interaction with the cut-off upper trough...land interaction with the US Gulf coast later in the forecast period...and current poorly-organized nature of Erika's remnant which means Erika will take a while to re-organize if it does regenerate into a tropical cyclone.

Thermodynamic Outlook for the Forecast Period...This system will be over very favorable Gulf of Mexico waters at and above 30 deg C thru the forecast period.

24 Hr Forecast (0000Z Aug 31)...Remnant surface trough in the eastern Gulf of Mexico with vorticity maximum centered at 25N-84W

48 Hr Forecast (0000Z Sep 1)...Remnant surface low in the central Gulf of Mexico centered at 27N-89W

72 Hr Forecast (0000Z Sep 2)...35 mph maximum sustained wind tropical depression in north-central Gulf of Mexico just offshore of Alabama centered at 29N-89W

96 Hr Forecast (0000Z Sep 3)...40 mph maximum sustained wind tropical storm centered just offshore of the Florida/Alabama border...centered at 29.5N-87W

120 Hr Forecast (0000Z Sep 4)...Remnant low over southern Alabama centered at 31N-86W

...SPECIAL FEATURE...TROPICAL LOW INVEST 99-L...
Current Prognosis...The tropical wave just offshore of the west coast of Africa has rapidly organized into a healthy tropical low pressure spin (designated as Invest 99-L on the Naval Research Laboratory site of the US Navy). The tropical low features a central dense overcast surrounded by sprial bands...and therefore could be upgraded to a tropical depression or tropical storm at any time. Satellite animation shows that the well-defined center of circulation has taken a 6-hourly northwestward motion from 10N-16.5W as of 1800Z to 10.8N-17.8W as of 0000Z. The most recent satellite image at 0300Z suggests the center may be wobbling straight north at the moment while arriving to 11.5N-17.8W.

Atmospheric Outlook for the Forecast Period...The surface subtropical ridge in the eastern Atlantic is re-organizing further north around what is currently the 1024 mb center just northwest of the Azores supported by upper convergence on the back side of the eastern Atlantic upper trough (marked by blue-dashed line on the right side of the above atmopsheric features chart). This northward re-location of the surface ridge has allowed this system to track to the right of my previous forecast track as this system is already tracking northwestward...and perhaps northward as noted at the end of the above current prognosis section (this has caused me to adjust the early part of my updated forecast track below to the right of my previous). By 48 hours as the eastern Atlantic surface ridge strengthens and as this system runs into the ridge...I expect the track to bend back toward the west. This system was previously expected to interact with a ridge weakness associated with a strong frontal cyclone and associated upper vortex moving into the north-central Atlantic from eastern Canada. Because of the rightward adjustment in my short-term forecast track...I now expect this system to stay to the right of the ridge weakness...with the weakness filling in after 96 hours when the frontal cyclone and its upper vortex lifts out to the north. Therefore the later part of my updated forecast track becomes slightly southwest of my previous as this system no longer falls into the weakness. As far as the favorablility of upper winds...for the most part this system will be under favorable low shear and enhanced outflow of the eastern tropical Atlantic upper ridge marked by the blue-zig-zag line in the lower-right of the above atmospheric features chart. In the next 24 hours...the eastern Atlantic upper trough will leave behind a cut-off upper vortex just northwest of the Cape Verde Islands which is still forecast to weaken. However tonight's GFS model run does not weaken this upper vortex as fast as it did yesterday...and therefore this system could struggle with some westerly shear in the 72 to 96 hour timeframe before the upper vortex dissipates.

Thermodynamic Outlook for the Forecast Period...The above thermodynamics chart shows that the waters in the Cape Verde Islands region have warmed a bit...with the 26 deg C isotherm shifting northward. However the chart also shows some dry Saharan air over the Cape Verde Islands...and the saharan air layer (SAL) analysis from CIMSS also shows a belt of dry air just north of the islands. I initally increased my intensity forecast due to the rapid organization noted in the above current prognosis...followed by a leveling of the strength through 96 hours as the rightward adjusted forecast track now sets the circulation to track straight northward into this dry air in the short term (plus this system may also deal with a bit of shear at 72 to 96 hrs as noted in the above atmo outlook section). I then finally start ramping up the intensity at the end of the forecast (120 hours) as the possible shear diminishes and as this system moves more westward into warmer waters which could help this system fire some storm bursts that fight off the dry air.

24 Hr Forecast (0000Z Aug 31)...50 mph maximum sustained wind tropical storm just offshore of Africa and east-southeast of the Cape Verde Islands...centered at 14N-18.5W

48 Hr Forecast (0000Z Sep 1)...50 mph maximum sustained wind tropical storm just east of the Cape Verde Islands...centered at 16N-21W

72 Hr Forecast (0000Z Sep 2)...50 mph maximum sustained wind tropical storm centered very near the northwest Cape Verde Islands after passing through the islands...centered at 17.5N-26W

96 Hr Forecast (0000Z Sep 3)...50 mph maximum sustained wind tropical storm centered at 18.5N-31W

120 Hr Forecast (0000Z Sep 4)...60 mph maximum sustained wind tropical storm centered at 19N-36W

2015 Atlantic Hurricane Season Birdseye Discussion #71

By: NCHurricane2009, 5:10 AM GMT on August 29, 2015

...SATURDAY AUGUST 29 2015 1:11 AM EDT...
Tropical Storm Erika a flash flood and mudslide threat to Hispaniola (Haiti and the Dominican Republic) and perhaps Cuba as we progress through the day today. Erika is then expected to track into the eastern Gulf of Mexico and move into the southeastern United States from Florida...see special feature section below for a detailed update on Erika. Continue visiting www.nhc.noaa.gov for up to the minute latest information on Erika including watches and warnings.

Elsewhere...the vigorous tropical wave over western Africa has shifted southwestward away from the unfavorable upper trough currently in the eastern Atlantic (marked by blue-dashed line on the right side of the atmospheric features chart below). In addition the tropical wave continues to show rotation and some signs of organization on satellite animation...and therefore I have upgraded the tropical wave to a special feature on this blog. See second special feature section below for additional details on this tropical wave. It should be noted this tropical wave has potential to move into the Cape Verde Islands while developing into a tropical cyclone over the next 72 hours...and therefore interests in these islands should closely monitor this tropical wave.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL STORM ERIKA...
Current Prognosis...Erika continues to have a broad surface center with a thunderstorm complex that remains biased to the east of the center due to westerly shear from what is left of a weakening TUTT (Tropical Upper Tropospheric Trough) in the area (marked by a blue L to the left of Erika in the above atmopsheric features chart). Tonight's 0000Z fix was centered over southern Hipsaniola (Haiti and the Dominican Republic) at 18.3N-72.0W...which is very close to but a little west of my previous track forecast. The thunderstorm complex of Erika remains strong while producing a flash flood rain threat and gusty winds over Hispaniola.

Atmospheric Outlook for the Forecast Period...Through the forecast period...the track of Erika is expected to bend increasingly to the north in response to a low-level ridge weakness created by upper-level divergence on the east side of the cut-off upper trough in the western Gulf of Mexico (marked by blue-dashed line in the above atomspheric features chart). However...the track of Erika is not expected to bend immediately to the north because of the 1024 mb surface ridge over the eastern United States currently building north of Erika...supported by upper convergence on the west side of the deep-layered frontal system moving into the northwest Atlantic from eastern Canada and the northeastern US. It is not until the end of the forecast period that Erika could bend completely northward in track as it becomes strong/tall enough to feel the influence of the aforementioned cut-off upper trough. If Erika follows my forecast track shown below...Erika will be centered close to the cut-off upper trough...resulting in a possible transition to a large...broad tropical storm supported by widespread divergence on the east side of the cut-off upper trough...featuring a comma shaped storm mass biased to the east half of the circulation as the cut-off upper trough blocks activity on the west side of Erika.

Thermodynamic Outlook for the Forecast Period...This system is currently over 29 deg C waters...and will be tracking toward a very favorable thermodynamic environment as it moves into waters above 30 deg C and a more moist air mass over the Gulf of Mexico and western Atlantic that can be seen in the above thermodymamics chart.


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

24 Hr Forecast (0000Z Aug 30)...Remnant Tropical Wave with vorticity maximum over eastern Cuba...centered at 21N-78W

48 Hr Forecast (0000Z Aug 31)...40 mph maximum sustained wind tropical storm centered between on the north coast of Cuba and just south of the Florida Peninsula at 23.5N-81W

72 Hr Forecast (0000Z Sep 1)...45 mph maximum sustained wind tropical storm centered over the eastern Gulf of Mexico...at 26N-84W

96 Hr Forecast (0000Z Sep 2)...60 mph maximum sustained wind tropical storm approaching the Florida Panhandle coast...centered over the northeastern Gulf of Mexico at 28N-86W

120 Hr Forecast (0000Z Sep 3)...45 mph maximum sustained wind tropical storm centered over the Florida Panhandle...at 30.5N-86W

Track Forecast...My updated track forecast is slightly west of my previous to account for the fact that the intial position of the storm is a bit west of my previous as noted in the above current prognosis section. Note the slow northward track by the end of the forecast period...because the eastern US surface ridge is expected to be nearly stationary thru the forecast period...which means it will become a blocking feature as the western Gulf of Mexico cut-off upper trough tries to steer it northward.

Intensity Forecast...I have made no changes to my intensity forecast. I continue to predict Erika will soon open into a tropical wave due to the unfavorable westerly shear and land interaction with Hispaniola noted in the above current prognosis...followed by re-generation as Erika finds itself in more favorable upper winds after the shearing TUTT element dissipates and as the storm moves into a very favorable thermodynamic environment (mentioned in the above thermodymamic outlook). My forecast strenghtening rate by the end of the forecast period remains on the gradual side because Erika's west side will be suppressed by the western Gulf of Mexico cut-off upper trough (mentioned in the above atmo outlook).

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track with some shrinkage in anticipation that Erika opens into a tropical wave...followed by re-growth with the assumption that Erika transitions into a broad system in the eastern Gulf of Mexico as mentioned in the last sentence of the above atmospheric outlook section. A flash flood and mudslide threat is currently in progress over Hispaniola (Haiti and the Dominican Republic)...and this threat will shift into eastern Cuba over the next 24 hours (I think Erika will continue to be too far south of the Bahamas such that rain..but not heavy rain...is more likely there). Heavy rains spreading across Florida and into the southeastern United States are possible by the end of the forecast period if Erika transitions into the large-broad type of tropical storm mentioned at the end of the above atmospheric outlook section.

...SPECIAL FEATURE...TROPICAL WAVE EMERGING FROM AFRICA...
Current Prognosis...The tropical wave currently emerging from Africa appears to have a tropical low pressure spin currently centered on the west African coast at 10N-14W. Satellite animation over the last 24 hours suggests the tropical wave has moved southwestward perhaps as the 1020 mb surface ridge in the eastern Atlantic has undergone a southward shift in advance of the surface frontal boundary in the northeast Atlantic supported by the upper trough currently in the eastern Atlantic (marked by blue-dashed line on the right side of the above atmospheric features chart).

Atmospheric Outlook for the Forecast Period...The northeast Atlantic surface frontal boundary supported by the eastern Atlantic upper trough will continue to erode the 1020 mb eastern Atlantic surface ridge...causing the surface ridge to re-organize further north around what is currently the 1023 mb center just east of Newfoundland supported by upper convergence on the back side of the eastern Atlantic upper trough. As the surface ridge re-organizes further north...this will cause the track of the tropical wave to bend northwestward toward the Cape Verde Islands. A strong frontal cyclone and associated upper vortex will then move into the north-central Atlantic from eastern Canada and maintain the northwest track of the wave. At the end of the forecast period (120 hrs)...the north-central Atlantic frontal cyclone and upper vortex will being to lift out to the north and allow the Atlantic surface ridge to start rebuilding north of the tropical wave...which is why I bend the forecast track more westward by that time. As far as the favorablility of upper winds...this tropical wave will be under favorable low shear and enhanced outflow of the eastern tropical Atlantic upper ridge marked by the blue-zig-zag line in the lower-right of the above atmospheric features chart...with the exception of a brief period at 48 hours when the eastern Atlantic upper trough leaves behind a cut-off upper vortex just northwest of the Cape Verde Islands that could impart some southerly vertical shear. However this upper vortex will be weakening and moving away after 48 hours and therefore is not considered a big factor in my forecast below.

Thermodynamic Outlook for the Forecast Period...The above thermodynamics chart shows that dry Saharan air is not nearly as prominent as it was earlier this month. However...considering the previous two tropical waves have ingested dry saharan air that was not readily visible in the above thermodynamics chart...I am treating this situation as if there is a small amount of dry Saharan air that will interact with this system as it moves northwestward toward the Cape Verde Islands. In addition...it will be moving toward the 26 deg C sea-surface temperature isotherm as it passes by the Cape Verde Islands. This is why I keep the intensification rate slow thru the first 96 hours...and then I finally start ramping up the intensity at the end of the forecast (120 hours) as the system moves more westward into warmer waters.

24 Hr Forecast (0000Z Aug 30)...Well-organized tropical low centered at 10N-18W

48 Hr Forecast (0000Z Aug 31)...35 mph maximum sustained wind tropical depression under sourtherly vertical shear...centered at 12.5N-21W

72 Hr Forecast (0000Z Sep 1)...45 mph maximum sustained wind tropical storm moving into the southern Cape Verde Islands...centered at 15N-24W

96 Hr Forecast (0000Z Sep 2)...50 mph maximum sustained wind tropical storm just west of the Cape Verde Islands...centered at 17.5N-27W

120 Hr Forecast (0000Z Sep 3)...65 mph maximum sustained wind tropical storm centered at 19N-30.5W

2015 Atlantic Hurricane Season Birdseye Discussion #70

By: NCHurricane2009, 5:43 AM GMT on August 28, 2015

...FRIDAY AUGUST 28 2015 1:45 AM EDT...
Tropical Storm Erika reforms to the southeast...and therefore appears to be on a trajectory that will line up with several periods of land interaction and less favorable upper winds that will keep the storm weaker as it ultimately tracks toward the Florida peninsula and southeastern United States. However this is a low confidence forecast situation as noted in the National Hurricane Center advisories throughout the day...therefore interests in the projected path of the storm (the northern Caribbean Sea Islands...the Bahamas...and southeastern United States) should continue to carefully monitor Erika. See special feature section below for an update on Erika. Continue visiting www.nhc.noaa.gov for up to the minute latest information on Erika including watches and warnings.

Elsewhere...the National Hurricane Center has introduced a tropical wave over western Africa into their tropical weather outlook. Because the last two tropical waves that have emerged from Africa have weakened due to dry Saharan air...and because an unfavorable upper trough currently in the eastern Atlantic (marked by two blue-dashed lines on the right side of the atmospheric features chart below) will shift eastward toward Africa...I am not considering upgrading this tropical wave to a special feature on this blog at this time.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 0000Z and 0119Z-released WPC analysis.

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL STORM ERIKA...
Current Prognosis...Because Erika featured a broad surface center supsectible to regenerating at a new location...and because the tropical storm had a strong thunderstorm complex that was sheared off to the southeast of the broad surface center...the broad surface center has reformed at a further southeast location. Not suprisinlgy then...tonight's 0000Z fix was at 16.7N-64.7W...which is well southeast of previous forecasts. Currently Erika is under light westerly shear as elements of a weakening TUTT (Tropical Upper Tropopsheric Trough) are located immediately west of the storm (these elements are marked by two blue Ls to the left of Erika in the above atmospheric features chart). The thunderstorm complex of Erika remains strong while continuing to produce flash flooding rains and gusty winds reaching tropical storm force over the northeastern Caribbean Islands...but the thunderstorm complex is biased to the east half of the circulation due to the aforementioned light westerly shear.

Atmospheric Outlook for the Forecast Period...Through the forecast period...the track of Erika is expected to bend increasingly to the north in response to a low-level ridge weakness created by upper-level divergence on the east side of a developing western Gulf of Mexico cut-off upper trough (tonight this low-level ridge weakness is well-defined as the upper divergence has produced a 1013 mb surface frontal depression near the Floria Panhandle). However...the track of Erika is not expected to bend immediately to the north because a surface ridge moving offshore from North America will build north of Erika...supported by upper convergence on the west side of the departing deep-layered frontal system which is about to emerge from eastern Canada and the northeastern US. It is not until the end of the forecast period that Erika could bend completely northward in track as it becomes strong/tall enough to feel the influence of the aforementioned cut-off upper trough. The track forecast below is a significant westward shift from my previous (reasoning is explained in the track forecast section below). If it follows the updated forecast track...Erika will be centered much closer to the cut-off upper trough...resulting in a possible transition to a large...broad tropical storm supported by widespread divergence on the east side of the cut-off upper trough and also featuring a comma shaped storm mass biased to the east half of the circulation as the cut-off upper trough blocks activity on the west side of Erika.

Thermodynamic Outlook for the Forecast Period...This system is currently over 29 deg C waters...and will be tracking toward a very favorable thermodynamic environment as it moves into waters above 30 deg C and a more moist air mass over the Gulf of Mexico and western Atlantic that can be seen in the above thermodymamics chart.


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

24 Hr Forecast (0000Z Aug 29)...45 mph maximum sustained wind tropical storm over the southern Hispaniola at 18.5N-71W

48 Hr Forecast (0000Z Aug 30)...Remnant Tropical Wave with vorticity maximum over eastern Cuba...centered at 21N-76.5W

72 Hr Forecast (0000Z Aug 31)...40 mph maximum sustained wind tropical storm centered between Cuba...Florida...and the Bahamas at 23.5N-79W

96 Hr Forecast (0000Z Sep 1)...45 mph maximum sustained wind tropical storm centered over the southwestern Florida peninsula coast...at 26N-82W

120 Hr Forecast (0000Z Sep 2)...60 mph maximum sustained wind tropical storm approaching the Florida Panhandle coast...centered over the northeastern Gulf of Mexico at 29N-84W

Track Forecast...Because of the southeastward center reformation described in the current prognosis...Erika is now aligned to track into Hispaniola and Cuba...with the resulting land interaction keeping Erika weaker and hence delaying when it becomes strong/tall enough to be influenced and be turned northward by the east side of the cut-off upper trough (mentioned in the atmo outlook section). Thus my updated forecast track is a significant westward shift compared to my previous.

Intensity Forecast...I have also significantly lowered my intensity forecast with Erika now likely to struggle with a direct landfall over the mountanious and large island of Hispaniola (Haiti and the Dominican Republic). In fact I currently predict Erika will open into a tropical wave...followed by a forecast regeneration just southeast of the Florida peninsula as Erika finds itself in more favorable upper winds after the shearing TUTT elements (mentioned in the current prognosis section) dissipate and due to very favorable thermodynamic parameters (mentioned in the above thermodymamic outlook). My forecast strenghtening rate by the end of the forecast period then remains on the gradual side due to land interaction with the Florida Peninsula and because Erika's west side will be suppressed by the cut-off upper trough (mentioned in the above atmo outlook) if she follows my updated forecast track.

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track with some shrinkage in anticipation that Erika opens into a tropical wave...followed by re-growth with the assumption that Erika transitions into a broad system in the eastern Gulf of Mexico as mentioned in the last sentence of the above atmospheric outlook section. The National Hurricane Center reported significant flash flooding and potential for mudslides over the Lesser Antilles due to heavy rains that have been occuring in Erika's thunderstorm complex...and therefore a flash flood and mudslide threat is possible for the Virgin Islands...Puerto Rico Hispaniola (Haiti and the Dominican Republic)...and eastern Cuba over the next few days (I think Erika will now be tracking too far south of the Bahamas such that rain..but not heavy rain...is more likely there). Heavy rains spreading across Florida and into the southeastern United States are possible by the end of the forecast period if Erika transitions into the large-broad type of tropical storm mentioned at the end of the above atmospheric outlook section.

2015 Atlantic Hurricane Season Birdseye Discussion #69

By: NCHurricane2009, 3:22 AM GMT on August 27, 2015

...WEDNESDAY AUGUST 26 2015 11:23 PM EDT...
Tropical Storm Erika doing well in an environment of northerly shear and dry air and therefore is now expected to survive and threaten land areas in the western Atlantic over the next few days while moving into a much more favorable environment for strengthening. The northern Caribbean Islands (northern Lesser Antilles...Virgin Islands...Puerto Rico...Haiti...and the Dominican Republic) are to receive tropical storm conditions over the next 48 hours. By day 3 and beyond...the Bahamas and southeastern United States (from Florida to the Carolinas) could be threatened by a hurricane strengthening into a major hurricane. Needless to say...this situation bears very close watching. See Erika special feature section below for additional details. Continue visiting www.nhc.noaa.gov for up to the minute latest information on Erika including watches and warnings.

Elsewhere...the vigorous tropical wave that has recently emerged from western Africa into the eastern tropical Atlantic has significantly weakened while ingesting dry saharan air...and therefore is not expected to develop. I have cancelled it as a special feature on this blog.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL STORM ERIKA...
Current Prognosis...As of 0000Z Tropical Storm Erika was centered at 16.7N-59.5W...with the thunderstorm activity continuing to be biased to the south half of the circulation as the north half remains suppressed by the adjacent dry saharan air mass seen in the bottom-center of the above thermodynamics chart. Another factor suppressing activity in the north half of the circulation is northerly wind shear induced by the tail end of a TUTT (Tropical Upper Tropospheric Trough) fragment marked by a blue-dashed line just northeast of Erika in the above atmospheric features chart. Despite the presence of the dry air and northerly wind shear...strong thunderstorm bursts in the south half of the circulation have prevented Erika from weakening today and therefore it appears imminent Erika will strike the northern Lesser Antilles...Virgin Islands...Puerto Rico...Haiti...and the Dominican Repbulic as a tropical storm over the next 48 hours.

Atmospheric Outlook for the Forecast Period...Through the forecast period...the track of Erika is expected to bend increasingly to the north in response to a low-level ridge weakness created by upper-level divergence on the east side of a cut-off upper trough to be left behind by the current 1005 mb deep-layered frontal cyclone currently over eastern North America. The track of Erika is not expected to bend immediately to the north because a surface ridge moving offshore from North America will build north of Erika...supported by upper convergence on the west side of the departing 1005 mb deep-layered frontal cyclone. It is not until the end of the forecast period that Erika could bend completely northward in track as it becomes strong/tall enough to feel the influence of the aforementioned cut-off upper trough. The forecast track of Erika means that Erika will be curving into a very favorable upper ridge in the western Atlantic that will supply this system with low vertical shear and enhanced upper outflow (this upper ridge is currently marked by a blue H due north of Erika in the above atmospheric features chart).

Thermodynamic Outlook for the Forecast Period...This system is currently over 29 deg C waters...and will be tracking toward a very favorable thermodynamic environment as it moves into waters above 30 deg C and a more moist air mass over the Gulf of Mexico and western Atlantic that can be seen in the above thermodymamics chart.


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

24 Hr Forecast (0000Z Aug 28)...50 mph maximum sustained wind tropical storm over Puerto Rico...centered at 18N-66W

48 Hr Forecast (0000Z Aug 29)...60 mph maximum sustained wind tropical storm over the north coast of Hispaniola at 20N-72W

72 Hr Forecast (0000Z Aug 30)...80 mph maximum sustained wind hurricane centered between Cuba and the Bahamas at 22.5N-77.5W

96 Hr Forecast (0000Z Aug 31)...100 mph maximum sustained wind hurricane centered over the western Bahamas at 26N-78.5W

120 Hr Forecast (0000Z Sep 1)...120 mph maximum sustained wind hurricane centered north of the Bahamas and offshore of the southeastern United States...at 29N-79W

Track Forecast...The 0000Z fix in the above current prognosis is closely aligned with my previous forecast track...and therefore I have made no changes to the early part of my track. However I have made a rightward adjustment to the later part of my track because computer model runs have reverted back to showing the forecast cut-off upper trough (mentioned in the above atmospheric outlook section) at a more eastward position...coupled with the fact Erika is likely to strengthen and be strong/tall enough to feel the influence of the upper trough.

Intensity Forecast...Because Erika has not weakened due to the northerly wind shear and dry air effects...I have increased my intensity forecast. My strengthening rate is initially shown to be slow due to land interaction with Puerto Rico and Hispaniola...followed by more rapid strengthening when Erika is forecast to clear land and take advantage of very warm waters above 30 deg C...a moist air mass...and low shear and enhanced upper outflow below a western Atlantic upper ridge as noted in the above atmospheric and thermodynamic outlook sections.

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track with some growth in anticipation that Erika will strengthen. Impacts to the northern Caribbean Islands (northern Lesser Antilles...Virgin Islands...Puerto Rico...Haiti and the Dominican Republic) over the next 48 hours will be heavy rains with possible flash flooding coupled with some tropical storm force winds. Beyond 48 hours...the Bahamas have a high chance of receiving tropical storm conditions...with some of the Bahamian islands possibly receiving hurricane conditions if Erika strengthens as forecast. By the end of the 5-day forecast period we could be talking about a hurricane...possibly a major hurricane...threatening the southeastern United States coast anywhere from Florida to the Carolinas. Needless to say...this situation bears close watching.

2015 Atlantic Hurricane Season Birdseye Discussion #68

By: NCHurricane2009, 4:15 AM GMT on August 26, 2015

...WEDNESDAY AUGUST 26 2015 12:15 AM EDT...
Tropical Storm Erika is currenlty struggling as it approaches the northeastern Caribbean Sea Islands (the northern Lesser Antilles...Virgin Islands...Puerto Rico...Haiti and the Dominican Republic). Even though Erika is currently struggling...interests in these islands...as well as Cuba...the Bahamas...Florida and the southeastern United States including the eastern Gulf of Mexico should continue to carefully monitor Erika as the storm will be finding a much more favorable environment if it survives the next couple of days. See special feature section below for an update on Erika. Visit www.nhc.noaa.gov for up to the minute latest information on Erika including watches and warnings.

The remnant of Danny has redeveloped thunderstorms within the last 24 hours. However the remnant is headed into the rugged island of Hispaniola...which is as large as Danny...and therefore Danny is not expected to survive the island and regenerate.

The tropical wave in the eastern tropical Atlantic...currently located west of the Cape Verde Islands...has become less organized while ingesting dry Saharan air and is no longer expected to develop. It has been dropped from the National Hurricane Center tropical weather outlook. I have also cancelled it as a special feature on this blog.

Yet another vigorous tropical wave is about to emerge from western Africa into the eastern tropical Atlantic. Because this tropical wave currently looks impressive on satellite and because it is headed into a generally favorable environment in the eastern tropical Atlantic...I have already upgraded it to a special feature on this blog. See second special feature section below for more details on this tropical wave.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL STORM ERIKA...
Current Prognosis...As of 0000Z Tropical Storm Erika was centered at 15.8N-53.6W...with the thunderstorm activity continuing to be biased to the south half of the circulation as the north half remains suppressed by the adjacent dry saharan air mass seen in the bottom-center of the above thermodynamics chart. Because Erika has been struggling due to the dry air ingestion...Erika has weakened over the last 24 hours.

Atmospheric Outlook for the Forecast Period...This system will initally be steered on a west-northwest course by the 1022 mb Atlantic surface ridge marked in the above atmospheric features chart. The tropical eastern Atlantic is covered by a favorable upper ridge that earlier helped Erika develop (marked by blue H and blue-zig-zag line in the lower-right of the above atmospheric features chart). Meanwhile beyond the upper ridge is a less favorable but weakening TUTT (Tropical Upper Tropospheric Trough...marked by a series of blue-dashed lines strecthing from the Caribbean Sea to the northeast Atlantic south of the Azores). Computer model runs have been consistent in showing that the TUTT will continue to weaken while the upper ridge currently located near Bermuda (marked by blue H) expands in its place...and therefore upper winds are expected to be generally favorable thru the forecast period...with the exception of a brief period during the next 24 hours when a southward shifting framgent of the weakening TUTT imparts northerly shear on Erika. During the second half of the forecast period...the track of this system is likely to bend more northward in response to a low-level ridge weakness created by upper-level divergence on the east side of an upper trough to be left behind by the current 1006 mb deep-layered frontal cyclone currently over eastern North America. The weakness however will be insufficient in curving Erika completely northward as a surface ridge builds north of Erika...supported by upper convergence on the west side of the departing 1006 mb deep-layered frontal cyclone.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over favorable 28 to 29 deg C waters in the early part of hte forecast period...increasing to extremly favorable 30 to 32 deg C if the system indeed makes it way to the waters between the Bahamas and Cuba by the end of the forecast period. The only unfavorable thermodynamic factor for Erika is the adjacent dry Saharan air (seen in the bottom-center of the above thermodynamics chart). If Erika can survive the dry air in the short term...then she will be rewarded by the end of the forecast period with a more moist air mass currently seen in the Gulf of Mexico and western Atlantic.


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

24 Hr Forecast (0000Z Aug 27)...30 mph maximum sustained wind tropical depression under northerly wind shear approaching the northern Lesser Antilles...centered at 16.5N-60W

48 Hr Forecast (0000Z Aug 28)...40 mph maximum sustained wind tropical storm over Puerto Rico...centered at 18N-66W

72 Hr Forecast (0000Z Aug 29)...45 mph maximum sustained wind tropical storm over the north coast of Hispaniola at 20N-72W

96 Hr Forecast (0000Z Aug 30)...60 mph maximum sustained wind tropical storm centered between Cuba and the Bahamas at 22.5N-77.5W

120 Hr Forecast (0000Z Aug 31)...80 mph maximum sustained wind hurricane centered over the Florida Keys at 25N-82W

Track Forecast...The 0000Z fix in the above current prognosis is closely aligned with my previous forecast track...and therefore I have made no changes to my track forecast. 24 hours ago I was considering showing Erika bending more northward in track for tonight's 120 hr forecast point in response to a strengthening and tall enough Erika feeling the influence of the upper trough mentioned at the end of the above atmo outlook section. Instead tonight my new 120 hr forecast point now continues Erika into south Florida because models show the upper trough at a further west location such that I believe the upper trough will be too far away to pull Erika northward at 120 hours irrespective of how weak/strong (shallow/tall) Erika is by that time.

Intensity Forecast...Erika has weakened due to dry air effects...and therefore I forecast Erika to weaken further to a tropical depression in the next 24 hours because Erika's troubles will be exacerbated by a burst of northerly wind shear noted in the above atmospheric outlook section. I then re-strengthen Erika as she will then be forecast to reach a more moist air mass and 30 to 32 deg C waters in the Gulf of Mexico and western Atlantic (noted in the above thermo outlook)...coupled with a favorable upper ridge near Bermuda in the western Atlantic (noted in the above atmospheric outlook section). My re-strengthening rate is initially shown to be slow due to land interaction with Puerto Rico and Hispaniola...followed by more rapid strengthening when Erika is forecast to clear land.

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track...but I interrput the swath during the next 24 hours as I forecast Erika to dip down into tropical depression strength during that time. Impacts to the northern Caribbean Islands (northern Lesser Antilles...Virgin Islands...Puerto Rico...Haiti and the Dominican Republic)...Bahamas...and possibly Cuba are likely within the next four days. The southeastern United States (especially Florida)...in addition to the eastern Gulf of Mexico region...should monitor the progress of Erika for potential impacts by day 5 and beyond.

...SPECIAL FEATURE...TROPICAL WAVE EMERGING FROM AFRICA...
Current Prognosis...Meteosat-9 infrared satellite animation over the last 24 hours shows that a large and impressive tropical wave...which has recently gained the appearance of a well-organized tropical low...has traveled very rapidly westward over western Africa from 5W longitude to 17W longitude in only 24 hours! Satellite organization suggests that the tropical low pressure center in the tropical wave is currently located at 12N-17W. Based on its current and well-organized satellite appearance and the favorable atmospheric and thermodynamic environment that lies ahead of it...I have upgraded this tropical wave to a special feature on this blog...even though none of the current computer model runs do not forecast it to develop and the National Hurricane Center has not yet introduced it in their tropical weather outlook.

Atmospheric Outlook for the Forecast Period...This system will be steered westward by the 1022 mb Atlantic surface ridge marked in the above atmosphericeatures chart. The rapid development and westward motion of this tropical wave thus far I think indicates that their is a strong mid-level African Easterly Jet...and so my forecast track philosophy below is to gradually slow the westward speed of the tropical wave to a more typical pace as the wave distances itself away from the easterly jet. Conditions will initially be favorable for this tropical wave to develop under the favorable low shear and enhanced upper outflow environment of an upper ridge in the eastern tropical Atlantic (marked by blue-zig-zag line in the lower-right of the above atmospheric features chart). Beyond the upper ridge is a less favorable but weakening TUTT (Tropical Upper Tropospheric Trough...marked by series of blue-dashed line from the Caribbean Sea to the northeast Atlantic south of the Azores). Even though the TUTT is weakening...it is still forecast to have some presence at the end of the 5-day forecast period...and if the forecast track below holds this system will be nearing the south side of the TUTT at day 5. Therefore my intensification forecast is on the conservative side due to potential interaction with the TUTT...the fact that this is currently a large ciruclation on satellite imagery which will take time to consolidate into a tropical cyclone if it were to develop...and the fact that none of the computer model runs tonight show development of this system.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over favorable 27 to 29 deg C sea surface temperatures thru the forecast period. Although their continues to be a dry Saharan air layer in the bottom-center of the above thermodynamics chart...an observation of the last few days worth of thermodynamics charts suggests the dry air mass has been weakening due to the recent developments of Danny and Erika to the west and therefore I am currently treating this situation as if dry air will not be a major problem.

24 Hr Forecast (0000Z Aug 27)...Well-organized tropical low passing south of the Cape Verde Islands centered at 12.5N-26W

48 Hr Forecast (0000Z Aug 28)...35 mph maximum sustained wind tropical depression centered at 13.5N-34W

72 Hr Forecast (0000Z Aug 29)...45 mph maximum sustained wind tropical storm centered at 14.5N-40W

96 Hr Forecast (0000Z Aug 30)...60 mph maximum sustained wind tropical storm centered at 15.5N-46W

120 Hr Forecast (0000Z Aug 31)...70 mph maximum sustained wind tropical storm centered at 16.5N-52W

2015 Atlantic Hurricane Season Birdseye Discussion #67

By: NCHurricane2009, 3:57 AM GMT on August 25, 2015

...MONDAY AUGUST 24 2015 11:58 PM EDT...
Tropical Storm Danny dissipates in the northeastern Caribbean Sea while Tropical Storm Erika comes to life in the central tropical Atlantic as the active pace of the 2015 Atlantic Hurricane Season continues...

The remnant of Danny has become weak on satellite pictures in the northeastern Caribbean Sea after its dissipation earlier today. The remnant has reverted to a more northward track in alignment toward the island of Hispaniola (Haiti and the Dominican Republic) while getting pulled toward a developing ridge weakness being generated by upper divergence on the southeast side of the upper trough associated with the deep-layered 1000 mb frontal cyclone currently over eastern North America. With the feeble remnant of Danny headed toward the rugged island of Hispaniola...which is as large as Danny...Danny is not expected to survive the island and regenerate.

Tropical wave Invest 98-L has become Tropical Storm Erika in the central tropical Atlantic this evening. Interests in the northeastern Caribbean Islands (the northern Lesser Antilles...Virgin Islands...Puerto Rico...Haiti and the Dominican Republic)...Cuba...and the Bahamas should take note that the TUTT (Tropical Upper Tropospheric Trough) that sheared apart Danny will be weakening as Erika moves in. Therefore Erika poses a bigger threat to these areas while forecast to arrive in 2 to 4 days. Interests in the southeastern United States including Florida should also monitor Erika as it is too early to know exactly what Erika will do just beyond the 5-day forecast period. See special feature section below for more info on Erika.

Elsewhere...the tropical wave in the eastern tropical Atlantic has not become any better organized as it might be struggling with some dry saharan air. If this trend continues for another 24 hours...I will be cancelling it as a special feature on this blog. For now...see second special feature section below for an update on this tropical wave.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 2211Z-released WPC analysis.

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL STORM ERIKA...
Current Prognosis...As of 0000Z newly-formed Tropical Storm Erika was centered at 14.5N-46.5W which is in alignment with the track forecast shown in discussion #65...and therefore I have reverted back to that forecast track. A central dense overcast of thunderstorms with spiral banding has been covering the south half of the circulation while the north half appears to be struggling a bit due to the adjacent dry saharan air mass seen in the bottom-center of the above thermodynamics chart.

Atmospheric Outlook for the Forecast Period...This system will initally be steered on a west-northwest course by the 1024 mb Atlantic surface ridge marked in the above atmospheric features chart. The tropical eastern Atlantic is covered by a favorable upper ridge that Erika has been taking advantage of (marked by blue H and blue-zig-zag line in the lower-right of the above atmospheric features chart). Meanwhile beyond the upper ridge is a less favorable but weakening TUTT (Tropical Upper Tropospheric Trough...marked by a series of blue-dashed lines strecthing from the Caribbean Sea to the northeast Atlantic south of the Azores). Computer model runs have been consistent in showing that the TUTT will weaken while the upper ridge currently located near the northern Bahamas (marked by blue H) expands in its place...and therefore upper winds are expected to be generally favorable thru the forecast period...with the exception of a brief period at 48 hours when a southward shifting framgent of the weakening TUTT imparts northerly shear on this system. By the end of the forecast period...the track of this system is likely to bend more northward in response to a low-level ridge weakness created by upper-level divergence on the east side of an upper trough to be left behind by the current 1000 mb deep-layered frontal cyclone currently over eastern North America. The low-level ridge weakness won't be very impressive...with a surface ridge re-developing due north of Erika due to western upper convergence on the west side of the departing deep-layered cyclone. But I still maintain the bend to the north through 120 hours as I forecast Erika will be strong and deep-layered enough to get pulled by the aforementioned upper trough.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over favorable 28 to 29 deg C waters in the early part of hte forecast period...increasing to extremly favorable 30 to 32 deg C if the system indeed makes it way to the waters between the Bahamas and Cuba by the end of the forecast period. The dry Saharan air adjacent to Erika (seen in the bottom-center of the above thermodynamics chart) hast not been much of a problem for Erika...with the low vertical wind shear in Erika's current environment allowing its moisture field to remain vertically stacked with the surface center...with the moisture field for the most part plowing the dry air out of the way. However there have been recent signs that some of this dry air has been supressing the north half of the circulation as noted in the above current prognosis...but for now will continue to assume that dry air won't be much of a problem for Erika.


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

24 Hr Forecast (0000Z Aug 26)...60 mph maximum sustained wind tropical storm centered at 15.5N-54W

48 Hr Forecast (0000Z Aug 27)...60 mph maximum sustained wind tropical storm under northerly wind shear approaching the northern Lesser Antilles...centered at 16.5N-60W

72 Hr Forecast (0000Z Aug 28)...65 mph maximum sustained wind tropical storm over Puerto Rico...centered at 18N-66W

96 Hr Forecast (0000Z Aug 29)...65 mph maximum sustained wind tropical storm over the north coast of Hispaniola at 20N-72W

120 Hr Forecast (0000Z Aug 30)...85 mph maximum sustained wind hurricane centered between Cuba and the Bahamas at 22.5N-77.5W

Track Forecast...Reverting back to the track forecast shown in discussion #65 due to the observations in the above current prognosis section.

Intensity Forecast...Erika is perfectly aligned with my previous intensity forecast...and therefore I have essentially used the same intensity forecast again...showing a leveling of the strength in the less favorable northerly shear environment at 48 hours (noted in the above atmo outlook section)...followed by slow strengthening due to land interaction with Puerto Rico and Hispaniola...followed by more rapid strengthening into a hurricane when Erika clears land and finds itself in favorable upper winds below a western Atlantic upper ridge and also over very favorable 30 to 32 deg C waters as noted in the above thermodynamic outlook.

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track with some growth to account for the forecast strengthening. Impacts to the northern Caribbean Islands (northern Lesser Antilles...Virgin Islands...Puerto Rico...Haiti and the Dominican Republic)...Bahamas...and possibly Cuba are likely within the next five days. The southeastern United States including Florida should monitor the progress of Erika for potential impacts just beyond the five day forecast period.

...SPECIAL FEATURE...EASTERN ATLANTIC TROPICAL WAVE...
Current Prognosis...Based on the latest Meteosat-9 infrared satellite image...the vigorous eastern Atlantic tropical wave has produced a tropical low that was centered just west-southwest of the Cape Verde Islands at 15N-28W as of 0000Z...which is slightly north and east of my previous track forecast and so my updated track forecast below is slightly north and east of the previous. Thunderstorm activity associated with the tropical wave has decreased over the last 24 hours and is confined to the eastern half of the circulation...perhaps suggesting that the north and west parts of the circulation are ingesting dry and stable saharan air not seen in the above thermodynamics chart.

Atmospheric Outlook for the Forecast Period...This system will be steered west-northwest by the 1024 mb Atlantic surface ridge marked in the above atmospheric features chart. The tropical eastern Atlantic is covered by a favorable upper ridge that this system is taking advantage of (marked by blue-zig-zag line in the lower-right of the above atmospheric features chart). Beyond the upper ridge is a less favorable but weakening TUTT (Tropical Upper Tropospheric Trough...marked by series of blue-dashed line from the Caribbean Sea to the northeast Atlantic south of the Azores). Although the TUTT is weakening...this system is expected to begin encounterinng some westerly shear from a fragment of the TUTT by 96 hours as reflected in the forecast below. However...I do not dissipate this system from the shear as the TUTT fragment is forecast to weaken continuously during the forecast period.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over favorable 27 to 29 deg C sea surface temperatures thru the forecast period. Although the above thermodynamics chart shows that this tropical wave is well-embedded in moisture...apparently the north and west halves of the circulation have lost thunderstorm activity perhaps from ingesting dry saharan air that is not readily visible in the chart. Therefore I have lowered my intensity forecast for this system and have delayed forecast tropical cyclone formation for another 24 hours. However if this trend continues...I will be cancelling this system as a special feature on this blog.

24 Hr Forecast (0000Z Aug 26)...Tropical low centered at 16N-35W

48 Hr Forecast (0000Z Aug 27)...40 mph maximum sustained wind tropical storm centered at 17N-40W

72 Hr Forecast (0000Z Aug 28)...50 mph maximum sustained wind tropical storm under westerly shear centered at 18N-45W

96 Hr Forecast (0000Z Aug 29)...35 mph maximum sustained wind tropical depression under westerly shear centered at 19N-50W

120 Hr Forecast (0000Z Aug 30)...35 mph maximum sustained wind tropical depression under southwesterly shear centered at 19.5N-55W

2015 Atlantic Hurricane Season Birdseye Discussion #66

By: NCHurricane2009, 3:14 AM GMT on August 24, 2015

...SUNDAY AUGUST 23 2015 11:14 PM EDT...
Although the northeastern Caribbean Sea islands are dealing with Tropical Storm Danny over the next 24 hours...interests in this region should also be watching tropical disturbance Invest 98-L which could become a tropical cyclone at any time and will already be moving into this region in 3 to 4 days. See first and second special feature section below for an update on Danny and 98-L. Elsewhere...a vigorous tropical wave that has recently emerged from Africa and into the tropical eastern Atlantic could also develop...see third special feature section below for an update on this tropical wave.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL STORM DANNY...
Current Prognosis...Wind shear and dry air continue to take their toll on Danny. The tropical cyclone continues to display itself as a weakening cloud swirl featuring occasional thunderstorm bursts northeast of the center. As of 0000Z the center of circulation passed over 15.5N-59.3W which is slightly south of my previous track forecast.

Atmospheric Outlook for the Forecast Period...Danny is situated between a tropical upper ridge to his east (marked by blue zig-zag line in the above atmospheric features chart) and tropical upper tropospheric trough (TUTT) to his north and west (marked by series of four blue Ls from the Caribbean Sea all the way to the northeast Atlantic south of the Azores)...with upper southwesterlies not aligned with the forward travel of Danny between these two upper-level features imparting shear on Danny. The 1026 mb Atlantic surface ridge will continue to steer Danny westward into these upper southwesterly winds.

Thermodynamic Outlook for the Forecast Period...Danny will be tracking over favorable 28 to 29 deg C waters through the forecast period...but thermodynamic conditions are no longer favorable for Danny as wind shear continues to push dry Saharan air surrounding the storm (seen in the bottom-center of the above thermodynamics chart) into the circulation.


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

24 Hr Forecast (0000Z Aug 25)...Tropical wave in the eastern Carribean Sea with vorticity maximum centered at 15.5N-64W

Track Forecast...I have updated my track forecast to be slightly south of my previous because of the observations noted in the current prognosis section.

Intensity Forecast...Because Danny continues to collapse in the dry air and shear environment and these conditions will persist for another 24 hours...I am forecasting that Danny will become a remnant tropical wave in the eastern Caribbean Sea in the next 24 hours.

Impact Forecast...Danny will be crossing the northern Lesser Antilles during the overnight into tomorrow morning...afterwards passing just south of the Virgin Islands and Puerto Rico. It is possible that Danny will fire clumps of showers and thunderstorms over these islands over the next 24 hours...but no signficant impacts are expected.

...SPECIAL FEATURE...TROPICAL WAVE INVEST 98-L...
Current Prognosis...As predicted yesterday...tropical low Invest 98-L is well-organized with spiral banding features in the thunderstorm clouds and is centered at 13.5N-39.5W. Despite following my previous forecast fairly well...I have adjusted my track forecast to be a little south of my previous because the circulation is currently traveling straight west instead of west-northwest.

Atmospheric Outlook for the Forecast Period...This system will be steered westward by the 1026 mb Atlantic surface ridge marked in the above atmospheric features chart. Although this system is currently moving rapidly westward...computer model runs gradually slow the forward speed thru the forecast period as the surface ridge gradually weakens. The tropical eastern Atlantic is covered by a favorable upper ridge (marked by blue-zig-zag line in the lower-right of the above atmospheric features chart). Meanwhile beyond the upper ridge is a less favorable TUTT (Tropical Upper Tropospheric Trough...marked by four blue Ls strecthing from the Caribbean Sea to the northeast Atlantic south of the Azores). Computer model runs have been consistent in showing that the TUTT will weaken while the upper ridge currently located near the northern Bahamas (marked by blue H) expands in its place...and therefore upper winds are expected to be generally favorable thru the forecast period...with the exception of a brief period at 72 hours when one of the upper vortices of the weakening TUTT (currently near 30N-45W) dives south and imparts northerly shear on this system. Because this system is organizing faster than I previously thought...my intensity forecast below is initially bumped up...followed by a leveling of the strength in the less favorable upper winds at 72 hours...followed by re-strengthening beyond 72 hours. By the end of the forecast period...the track of this system is likely to bend more northward in response to a low-level ridge weakness created by upper-level divergence on the east side of an upper trough to be left behind by the current 997 mb frontal cyclonic system currenlty over the north-central US.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over 28 to 29 deg C sea surface temperatures thru the forecast period. The dry Saharan air to the west of 98-L (seen in the bottom-center of the above thermodynamics chart) does not appear to be a problem for 98-L...with the low vertical wind shear in 98-L's environment allowing its moisture field to remain vertically stacked with the surface center...with the moisture field plowing the dry air out of the way.

24 Hr Forecast (0000Z Aug 25)...45 mph maximum sustained wind tropical storm centered at 13.5N-47W

48 Hr Forecast (0000Z Aug 26)...60 mph maximum sustained wind tropical storm centered at 14.5N-54W

72 Hr Forecast (0000Z Aug 27)...60 mph maximum sustained wind tropical storm under northerly wind shear approaching the northern Lesser Antilles...centered at 15.5N-60W

96 Hr Forecast (0000Z Aug 28)...65 mph maximum sustained wind tropical storm with center passing just south of Puerto Rico...centered at 16.5N-66W

108 Hr Forecast (1200Z Aug 28)...75 mph maximum sustained wind hurricane making landfall on south coast of Dominican Republic...centered at 17.5N-69W

120 Hr Forecast (0000Z Aug 29)...65 mph maximum sustained wind tropical storm centered over Hispaniola (Haiti and the Dominican Republic) at 18.5N-72W

...SPECIAL FEATURE...EASTERN ATLANTIC TROPICAL WAVE...
Current Prognosis...Based on the latest Meteosat-9 infrared satellite image...the vigorous tropical wave that has recently emerged from west Africa into the Atlantic has an expansive area of showers and thunderstorms...with the organization of this activity suggesting that the vorticity maximum of the wave is southeast of the Cape Verde Islands at 13.5N-23W. Because the wave is not organizing as fast as I thought it previously would...I have delayed tropical cyclone formation in my forecast below by 24 hours.

Atmospheric Outlook for the Forecast Period...This system will be steered by the 1026 mb Atlantic surface ridge marked in the above atmospheric features chart. The tropical eastern Atlantic is covered by a favorable upper ridge that this system is taking advantage of (marked by blue-zig-zag line in the lower-right of the above atmospheric features chart). Beyond the upper ridge is a less favorable TUTT (Tropical Upper Tropospheric Trough...marked by four blue Ls from the Caribbean Sea to the northeast Atlantic south of the Azores). Although computer model runs have been consistent in showing that the TUTT will weaken...models consistenly show that the upper vortex near 30N-45W in the weakeneing TUTT will dive south and begin to impart unfavorable westerly shear on this system later in the forecast period. It was previously thought this upper vortex would also team up with what is left of Invest 97-L to create a break in the Atlantic surface ridge that would deflect the track north...but the GFS model has cancelled this solution and so I now show this system continuing west-northwest thru the forecast period.

Thermodynamic Outlook for the Forecast Period...This system is currently over very favorable 29 to 30 deg C waters...and will be tracking over favorable 28 to 29 deg C sea surface temperatures thru the forecast period. With 98-L to its west plowing away the dry Saharan air seen in the bottom-center of the above thermodynamics chart...not expecting dry air to be a problem for this system.

24 Hr Forecast (0000Z Aug 25)...Tropical low centered west-southwest of the Cape Verde Islands at 14.5N-29W

48 Hr Forecast (0000Z Aug 26)...35 mph maximum sustained wind tropical depression centered at 15.5N-36W

72 Hr Forecast (0000Z Aug 27)...50 mph maximum sustained wind tropical storm centered at 16.5N-41W

96 Hr Forecast (0000Z Aug 28)...60 mph maximum sustained wind tropical storm under westerly shear centered at 17.5N-46W

120 Hr Forecast (0000Z Aug 29)...50 mph maximum sustained wind tropical storm under westerly shear centered at 18N-51W

2015 Atlantic Hurricane Season Birdseye Discussion #65

By: NCHurricane2009, 4:42 AM GMT on August 23, 2015

...SUNDAY AUGUST 23 2015 12:45 AM EDT...
While approaching the northeastern Caribbeean Sea islands...Danny has rapidly weakened from a category 2 hurricane to a tropical storm within the last day as wind shear and dry air have finally begun taking its toll on this system. See special feature section below for an update on Tropical Storm Danny. Visit www.nhc.noaa.gov for up to the minute lastest information on Danny...including tropical storm advisories which are currently in effect for some of the northeastern Caribbean islands.

Computer models continue to suggest there is potential for vigorous tropical waves to the east of Danny to also develop. See second special feature section below concerning the vigorous tropical wave which has moved from the waters southeast of the Cape Verde Islands to the waters southwest of the islands while becoming better organized into a tropical low that has recently been upgraded to Invest 98-L. It should be noted that 98-L is moving faster than Danny did and will already reach the northeastern Caribbean Islands by day 5 if it does develop. Another vigorous tropical wave has moved from interior western Africa and onto the west coast and is about to emerge into the Atlantic. I have upgraded this tropical wave to a special feature on this blog as it too has become better organized...see the third special feature section below for additional details and an outlook on this wave.

Elsewhere...subtropical disturbance Invest 97-L located in the western Atlantic just northwest of Bermuda continues to lack a tight surface center and therefore has run out of time to develop before conditions become more hostile by 48 hours. I have cancelled it as a special feature on this blog.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL STORM DANNY...
Current Prognosis...Just as Danny proved small circulations can rapidly intensify....Danny over the last 24 hours has demonstrated that small circulations can also rapidly weaken...going from a high-end category 2 hurricane to a tropical storm while while wind shear has finally pushed aside the storm canopy of the small circulation and allowed dry air to penetrate. As of 0000Z the center of circulation passed over 15.6N-54.1W which is slightly southwest of my previous track forecast. Danny has essentially lost all significant thunderstorm activity with the exception of bursts that are firing just northeast of the center.

Atmospheric Outlook for the Forecast Period...Danny is situated between a tropical upper ridge to his east (marked by blue H in the above atmospheric features chart) and tropcial upper tropospheric trough (TUTT) to his north and west (marked by four blue Ls)...with upper southwesterlies not aligned with the forward travel of Danny between these two upper-level features imparting shear on Danny. The 1029 mb Atlantic surface ridge will continue to steer Danny westward into these upper southwesterly winds...but these winds will not be severe on Danny because the TUTT will be simultaneously weakening. Hence in my updated forecast below I do not immediately dissipate Danny.

Thermodynamic Outlook for the Forecast Period...Danny will be tracking over favorable 28 to 29 deg C waters through the forecast period...but thermodynamic conditions are no longer favorable for Danny as wind shear has finally pushed aside his storm canopy and allowed the dry Saharan air surrounding the storm (seen in the bottom-center of the above thermodynamics chart) to penetrate the circulation.


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

24 Hr Forecast (0000Z Aug 24)...40 mph max sustained wind tropical storm centered at 16N-59W

48 Hr Forecast (0000Z Aug 25)...40 mph max sustained wind tropical storm centered just south of the Virgin Islands at 17N-64W

72 Hr Forecast (0000Z Aug 26)...40 mph max sustained wind tropical storm making landfall in the eastern Dominican Republic opening into a tropical wave...centered at 18N-69W

Track Forecast...I have updated my track forecast to be slightly southwest of my previous because of the observations noted in the current prognosis section. With Danny being further southwest than previously forecast...he has an increased chance of tracking into the mountainous island of Hispaniola (Haiti and the Dominican Republic) which is larger than the small circulation of this storm...and therefore I forecast Danny to dissipate at 72 hours when he reaches the longitudes of Hispaniola.

Intensity Forecast...My previous two intensity forecasts were nearly correct as far as predicting the peak intensity of Danny...but were incorrect in predicting when Danny would move into wind shear and rapidly weaken as this has happened 24 hours earlier than I predicted. Because the upper southwesterly winds that are currently shearing the storm are not expected to be severe (as noted in the above atmospheric outlook section)...in my updated intensity forecast I hold on to Danny as a weak tropical storm and wait to dissipate it until landfall at 72 hours.

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

...SPECIAL FEATURE...TROPICAL WAVE INVEST 98-L...
Current Prognosis...Satellite animation of this tropical wave over the last 24 hours showed heavy thunderstorms firing near and over the southern Cape Verde Islands which have since oragnized into a new surface tropical low pressure spin centered southwest of the Cape Verde Islands located at 13N-30W as of 0000Z. This is further north and west of where I predicted that a tropical low would organize and therefore I have adjusted my forecast track below accordingly. Recent satellite images show that the tropical low has been losing thunderstorm activity over the last 12 hours.

Atmospheric Outlook for the Forecast Period...This system will be steered westward by the 1029 mb Atlantic surface ridge marked in the above atmospheric features chart. Satellite animation shows that the new tropical low pressure circulation has been moving at a rapid westward clip of nearly 5W per 12 hours (or nearly 10W per 24 hours)...and computer models suggest this rapid westward motion will continue for another 24 hours. However computer model runs gradually slow the westward speed of this system thru the forecast period as the surface ridge gradually weakens. The tropical eastern Atlantic is covered by a favorable upper ridge (marked by blue-zig-zag line and blue H in the lower-right of the above atmospheric features chart). Meanwhile the tropical western Atlantic is covered by a less favorable TUTT (Tropical Upper Tropospheric Trough...marked by four blue Ls to the northwest of Danny). However...computer model runs have been consistent in showing that the TUTT will weaken while the upper ridge currently located near the Florida Peninsula (marked by blue H) expands in its place...and therefore upper winds are expected to be generally favorable for this tropical wave thru the forecast period.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over 28 to 29 deg C sea surface temperatures thru the forecast period. There is some uncertainty as to whether or not this system will ingest the unfavorable dry Saharan air seen in the bottom-center of the above thermodynamics chart...especially since this system has organized further northwest closer to this dry air and is moving rapidly westward into this dry air. This is why I have lowered my intensity forecast on this system relative to 24 hours ago.

24 Hr Forecast (0000Z Aug 24)...Well-organized tropical low centered at 13.5N-39W

48 Hr Forecast (0000Z Aug 25)...35 mph maximum sustained wind tropical storm centered at 14.5N-47W

72 Hr Forecast (0000Z Aug 26)...45 mph maximum sustained wind tropical storm centered at 15.5N-54W

96 Hr Forecast (0000Z Aug 27)...50 mph maximum sustained wind tropical storm approaching the northern Lesser Antilles...centered at 16.5N-60W

120 Hr Forecast (0000Z Aug 28)...60 mph maximum sustained wind tropical storm making landfall in southeastern Puerto Rico...centered at 17.5N-66W

...SPECIAL FEATURE...TROPICAL WAVE EMERGING FROM AFRICA...
Current Prognosis...Based on the latest Meteosat-9 infrared satellite image...the vigorous tropical wave emerging from the west coast of Africa currently has the appearance of a broad tropical low pressure spin organizing at 12.5N-16W

Atmospheric Outlook for the Forecast Period...This system will initially be steered by the 1029 mb Atlantic surface ridge marked in the above atmospheric features chart. Like Invest 98-L immediately to the west...this system is expected to initially move quickly to the west and then gradually slow its forward speed as the surface ridge gradually weakens. The tropical eastern Atlantic is covered by a favorable upper ridge (marked by blue-zig-zag line and blue H in the lower-right of the above atmospheric features chart). Meanwhile the tropical western Atlantic is covered by a less favorable TUTT (Tropical Upper Tropospheric Trough...marked by four blue Ls to the northwest of Danny). Although computer model runs have been consistent in showing that the TUTT will weaken...the northeastern-most upper vortex of the TUTT may team up with what is left of Invest 97-L to create a mid-ocean break in the Atlantic surface ridge that turns this system northwestward while this upper vortex simulatenous dives southeast and begins unfavorably shearing this system at the end of the forecast period as reflected in the forecast below.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over 28 to 29 deg C sea surface temperatures thru the forecast period. There is some uncertainty as to whether or not this system will ingest the unfavorable dry Saharan air seen in the bottom-center of the above thermodynamics chart. However Invest 98-L ahead of this system may help moisten out some of this dry air which would help this system develop.

24 Hr Forecast (0000Z Aug 24)...Broad tropical low centered just southeast of the Cape Verde Islands centered at at 13N-23W

48 Hr Forecast (0000Z Aug 25)...Well-organized tropical low centered west-southest of the Cape Verde Islands at 14N-29W

72 Hr Forecast (0000Z Aug 26)...45 mph maximum sustained wind tropical storm centered at 15N-36W

96 Hr Forecast (0000Z Aug 27)...50 mph maximum sustained wind tropical storm centered at 16N-41W

120 Hr Forecast (0000Z Aug 28)...60 mph maximum sustained wind tropical storm under southwesterly shear centered at 18.5N-43.5W

2015 Atlantic Hurricane Season Birdseye Discussion #64

By: NCHurricane2009, 3:39 AM GMT on August 22, 2015

...FRIDAY AUGUST 21 2015 11:40 PM EDT...
Danny rapidly intensifies into the first major hurricane (category 3 or greater) of the season. However current expectation is that Danny will weaken back to a tropical storm by the time it reaches the northeastern Caribbean Islands in 3 to 4 days while encountering increasing wind shear. However these islands should very carefully watch Danny and not let their guard down if the wind shear forecast changes in a way that allows Danny to maintain hurricane strength while moving into this region. See special feature section below for additional details on Danny.

Computer models continue to suggest there is potential for vigorous tropical waves to the east of Danny to also develop. See third special feature section below concerning the vigorous tropical wave currently southeast of the Cape Verde Islands. Another vigorous tropical wave located over interior western Africa has been introduced into the National Hurricane Center 5-day tropical weather outlook...waiting to see how good this wave looks when it enters the Atlantic before upgrading it to a special feature on this blog.

Elsewhere...subtropical disturbance Invest 97-L located in the western Atlantic very close to Bermuda so far has not developed a tighter surface center and therefore is less likely to develop into a subtropical or tropical cyclone. However I am still keeping it as a special feature on this blog...see second special feature section below for an update on 97-L.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...HURRICANE DANNY...
Current Prognosis...As suspected last evening...Danny had the potential to strengthen rapidly as a compact tropical cyclone and indeed aircraft reconaissance this past afternoon confirmed that Danny had become a major category 3 hurricane with 115 mph maximum sustained winds. Danny had a pinhole eye during the time of the reconaissance mission which has since disappeared...indicating that Danny has begun weakening this eveing either due to an eye wall replacement cycle or due to increasing shear as he nears the TUTT mentioned in the atmopsheric outlook below. As of 0000Z...satellite showed that the center of Danny passed over 14.8N-49.2W which is consistent with my previous track forecast.

Atmospheric Outlook for the Forecast Period...Danny is situated between a tropical upper ridge to his east (marked by blue H in the above atmospheric features chart) and tropcial upper tropospheric trough (TUTT) to his north and west (marked by two blue Ls and purple L). As the 1027 to 1032 mb Atlantic surface ridge steers Danny west-northwest thru the forecast period...Danny will continue to track into the TUTT while the TUTT simultaneously weakens. In fact tonight's GFS model run shows the TUTT weakening faster than the run from this time yesterday...and therefore shear levels will be at a more moderate level and not at an elevated level. Hence I prefer at this time to not dissipate Danny at the end of the forecast period.

Thermodynamic Outlook for the Forecast Period...Danny will be tracking over favorable 28 to 29 deg C waters through the forecast period...but will continue to track westward into dry Saharan air seen in the bottom-center of the above thermodynamics chart. Because Danny appears to be very resilient in this dry air due to the current low shear environment...I do not expect dry air to be a problem for Danny until later in the forecast period when the storm is expected to move into a more moderate shear environment (as noted at the end of the above atmospheric outlook section).


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

24 Hr Forecast (0000Z Aug 23)...110 mph max sustained wind hurricane centered at 15.8N-53.5W

48 Hr Forecast (0000Z Aug 24)...70 mph max sustsained wind tropical storm centered at 16.8N-58.5W

72 Hr Forecast (0000Z Aug 25)...60 mph max sustained wind tropical storm moving across northern Lesser Antilles and Virgin Islands...centered at 17.8N-63.5W

96 Hr Forecast (0000Z Aug 26)...50 mph max sustained wind tropical storm moving into the east coast of the Dominican Republic...centered at 18.8N-68.5W

120 Hr Forecast (0000Z Aug 27)...50 mph max sustained wind tropical storm centered between Haiti...eastern Cuba...and eastern Bahamas at 20.5N-73.5W

Track Forecast...My forecast track is simply an update of my previous one as the previous one is currently doing well as noted in the above current prognosis section.

Intensity Forecast...Tiny circulations can easily rapidly intensify as proven by Danny this past afternoon. However tiny circulations can also rapidly weaken...and so I show a brisk weakening rate when Danny is expected to move into a moderate vertical shear environment which will finally push aside Danny's thunderstorm core and expose the tiny circulation to dry air ingestion. I then level off the weakening rate and do not dissipate Danny towards the end of the forecast period because tonight's GFS run suggests that the shearing TUTT maybe nearly gone by that time which would allow Danny to survive.

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track. If the above forecast holds...the northeastern Caribbean Islands (northern Lesser Antilles...Virgin Islands...Puerto Rico...and the Dominican Republic) will receive impacts from Danny in the 3 to 4 day timeframe. If Danny survives as I currently forecast...he could reach the Bahamas by day 5. Although Danny is currently expected to be a weakened tropical storm while passing over these areas...do not let your guard down in case the current wind shear forecast changes in a way that would allow Danny to maintain hurricane strength in this region.

...SPECIAL FEATURE...WESTERN ATLANTIC SUBTROPICAL DISTURBANCE INVEST 97-L...
Current Prognosis...A strong blocking upper ridge southeast of Newfoundland has pushed the parent upper vortex of this subtropical disturbance directly over the 1012 mb surface center...which is why the 1012 mb low is marked a deep-layered cyclonic circulation in the above atmospheric features chart. Using visible satellite animation just prior to sunset...I estimate the surface center to be located just south-southeast of Bermuda at 30N-64W...which is southeast of my previous track forecast and my updated track forecast below is adjusted accordingly. It should be noted that the 1012 mb surface low remains very broad without a tight center and therefore will take longer to become a tropical cyclone...which is why I have delayed subtropical/tropical cyclone formation in my forecast below by another 24 hours and show a lower peak strength as a result. If this system does not develop a tighter surface center in the next 24 hours...it will not have much more time to develop and I will cancel it as a special feature on this blog.

Atmospheric Outlook for the Forecast Period...A 1022 mb to 1032 mb blocking surface ridge is currently located north of this system as seen in the atmospheric features chart above. Beyond 24 hours...Invest 97-L will accelerate northward on the west side of the blocking surface ridge and in advance a frontal cyclone approaching from the United States. It should be noted that by 72 hours this system should be transitioning to non-tropical as it interacts with upper divergence on the east side of the upper vortex associated with the incoming frontal cyclone.

Thermodynamic Outlook for the Forecast Period...I forecast transition from current subtropical status to fully tropical status beyond 24 hours as the Invest 97-L accelerates northward away from its parent cold core upper vortex and below warm core upper ridging to amplify due to warm air advection in advance of the frontal cyclone forecast to approach from the US by that time. By 72 hours this system should be transitioning to non-tropical while crossing the 26 deg C isotherm into cooler waters and interacting with upper divergence on the east side of the upper trough associated with said frontal cyclone.

24 Hr Forecast (0000Z Aug 23)...Surface low centered just north of Bermuda at 33N-65W

48 Hr Forecast (0000Z Aug 24)...45 mph max sustsained wind tropical storm centered offshore of the eastern United States at 35N-67.5W

72 Hr Forecast (0000Z Aug 25)...45 mph max sustained wind tropical storm centered just offshore of Massachusetts at 40N-66W...beginning to transition into a non-tropical remnant low

...SPECIAL FEATURE...EASTERN ATLANTIC TROPICAL WAVE...
Current Prognosis...Baesd on the 0000Z infrared satellite image from Meteosat-9 and latest surface analysis from the National Hurricane Center TAFB...a semi-organized tropical wave axis featuring an expansive field of strong thunderstorms is at 20W longitude at a location southeast of the Cape Verde Islands. The tropical wave is in a region of moist air...warm 28 to 29 sea-surface temperatures...and favorable low vertical wind shear beneath an upper ridge covering the eastern tropical Atlantic. Therefore potential for tropical cyclone formation from this tropical wave is high.

Atmospheric Outlook for the Forecast Period...This system will be steered westward by the 1032 to 1027 mb Atlantic surface ridge marked in the above atmospheric features chart. It will be located below a favorable eastern tropical Atlantic upper ridge (marked by blue zig-zag line in the lower-right corner of the above atmospheric features chart) thru the forecast period.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over 28 to 29 deg C sea surface temperatures thru the forecast period. There is some uncertainty as to whether or not this system will ingest the strip of unfavorable dry Saharan air seen in the bottom-center of the above thermodynamics chart. Given that Danny has done well against this dry air in a low shear environemnt and that this tropical wave will be staying in a low shear environment thru the forecast period...my current assumption is that dry air will not be a problem for this tropical wave.

24 Hr Forecast (0000Z Aug 23)...Tropical wave organizing into tropical low south of the Cape Verde Islands centered at 11.5N-25W

48 Hr Forecast (0000Z Aug 24)...Well-organized tropical low centered at 11.5N-29W

72 Hr Forecast (0000Z Aug 25)...45 mph maximum sustained wind tropical storm centered at 12N-34W

96 Hr Forecast (0000Z Aug 26)...60 mph maximum sustained wind tropical storm centered at 13N-39W

120 Hr Forecast (0000Z Aug 27)...75 mph maximum sustained wind hurricane centered at 14N-44W

2015 Atlantic Hurricane Season Birdseye Discussion #63

By: NCHurricane2009, 3:31 AM GMT on August 21, 2015

...THURSDAY AUGUST 20 2015 11:31 PM EDT...
In the matter of about four days...the Atlantic Hurricane Season has rapidly escalated...going from zero to three areas of interest as follows...

Defiant Danny does well while moving into dry Saharan air due to low wind shear...intensifying into a compact hurricane midway between the Lesser Antilles and Cape Verde Islands while now at risk of rapid intensification. Danny is currently forecast to encounter increasing wind shear likely to weaken it back to a tropical storm as it moves into the northeastern Caribbean Islands in about 4 to 5 days. However these islands should not let their guard down if the wind shear forecast changes in a way that allows Danny to maintain hurricane strength while moving into this region. See special feature section below for additional details on Danny.

Computer models continue to suggest there is potential for vigorous tropical waves to the east of Danny to also develop. Satellite imagery suggests one such tropical wave is about to emerge from the west coast of Africa...and this tropical wave has been introduced into the National Hurricane Center tropical weather outlook. I have also upgraded this tropical wave to a special feature on this blog...see third special feature section below for additional details.

Elsewhere...an upper vortex just north of Bermuda has produced a new surface low pressure center just southwest of Bermuda that has already been upgraded to Invest 97-L due to its risk of becoming a subtropcial or tropical cyclone within the couple of days. See second special feature section below for an update on this situation.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...HURRICANE DANNY...
Current Prognosis...Danny has transitioned from a moderate strength and average sized tropical storm to an unusually compact category 1 hurricane within the last 24 hours. It appears the adjacent dry air eroded all of the outer thunderstorms of the circulation...with Danny consolidating into an ultra-compact tropical cyclone under a tight core of thunderstorms that has persisted with this circulation since last night. The only thing keeping Danny from dissipating from the dry air is that it is in a low vertical shear environment beneath an upper ridge in the eastern tropical Atlantic (marked by blue-zig-zag line in the lower-right corner of the above atmospheric features chart)...which is allowing the tight storm core to stay vertically aligned with the surface center. In fact because Danny is now such a compact tropical cyclone...it can easily rapidly intensify since vertical wind shear is expected to remain low over the next 24 hours. Satellite showed that the eye of Danny passed over 13.2N-46W as of 0000Z earlier this evening which lines longitude-wise with my preivous track forecast...but is about 1 latitude further north from my previous track forecast.

Atmospheric Outlook for the Forecast Period...The eastern tropical Atlantic is covered by a favorable upper ridge as marked by a blue-zig-zag line in the bottom-right of the above atmospheric features chart. Meanwhile a TUTT (Tropical Upper Tropospheric Trough) consisting of two upper vortices (marked by two blue Ls) is located to the north of this upper ridge. The 1027 to 1032 mb Atlantic surface ridge marked in the atmospheric features chart will steer Danny west-northwest thru the forecast period...with the tropical cyclone intially taking advantage of favrable upper winds below the upper ridge but then reaching unfavorable southwesterly shear on the south side of the TUTT by the end of the forecast period. However the TUTT will be weakening as Danny moves into it...which means shear levels will be moderate instead of high which is why in my latest intensity forecast I chose to keep Danny alive for the next five days instead of dissipating it before then (see intensity forecast section below for additional details).

Thermodynamic Outlook for the Forecast Period...Danny will be tracking over favorable 28 to 29 deg C waters through the forecast period...but will continue to track westward into dry Saharan air seen in the bottom-center of the above thermodynamics chart. Because Danny appears to be very resilient in this dry air due to the current low shear environment (as noted in the above current prognosis section)...I do not expect dry air to be a problem for Danny until later in the forecast period when the storm is expected to move into a more moderate shear environment (as noted at the end of the above atmospheric outlook section).


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

24 Hr Forecast (0000Z Aug 22)...110 mph max sustained wind hurricane centered at 14.8N-49W

48 Hr Forecast (0000Z Aug 23)...110 mph max sustained wind hurricane centered at 15.8N-52.5W

72 Hr Forecast (0000Z Aug 24)...70 mph max sustsained wind tropical storm centered at 16.8N-58.5W

96 Hr Forecast (0000Z Aug 25)...60 mph max sustained wind tropical storm moving across northern Lesser Antilles and Virgin Islands...centered at 17.8N-63.5W

120 Hr Forecast (0000Z Aug 26)...50 mph max sustained wind tropical storm moving into the east coast of the Dominican Republic...centered at 18.8N-68.5W

Track Forecast...As noted in the above current prognosis section...Danny is about 1 latitude further north of my previous track forecast. In addition...Danny has made a bit of a turn towards the north as the Atlantic surface ridge re-organizes further north around the 1032 mb center just southeast of Newfoundland...with Danny expected to turn back toward a more westward track after the surface ridge re-organzies. These observations force me to make a northward adjustment in my forecast track. Recent computer model runs also show a slightly faster westward track compared to what was shown previously...and therefore I have adjusted my later forecast points to be a bit further to the west.

Intensity Forecast...Danny is stronger than my previous intensity forecast. In case the storm rapidly intensifies in the next 24 hours due to its compact structure...I have raised my intensity forecast points for 24 and 48 hours to maximal category 2 strength. And because tiny circulations can also rapidly weaken...I then show a brisk weakening rate as Danny starts moving into a moderate vertical shear environment which will finally push aside Danny's thunderstorm core and expose the tiny circulation to dry air ingestion. The only reason I don't show Danny dissipate before day 5 is because the shear is expected to be moderate instead of high as noted at the end of the above atmospheric outlook section.

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track. If the above forecast holds...the northeastern Caribbean Islands (northern Lesser Antilles...Virgin Islands...Puerto Rico...and the Dominican Republic) will receive a direct strike from Danny in the 4 to 5 day timeframe. Although Danny is currently expected to be a weakening tropical storm while passing over these areas...do not let your guard down in case the current wind shear forecast changes in a way that would allow Danny to maintain hurricane strength in this region.

...SPECIAL FEATURE...WESTERN ATLANTIC SUBTROPICAL DISTURBANCE INVEST 97-L...
Current Prognosis...An upper vortex is currently located just north of Bermuda and is marked by a blue L in the above atmospheric features chart. Split flow upper divergence between the south side of the upper vortex and east side of an upper ridge over the northern Gulf of Mexico (marked by blue H) has resulted in the formation of a weak and broad 1012 mb surface low pressure spin estimated (using visible satellite animation) to be centered southwest of Bermuda at 30N-67.5W. The heaviest thunderstorm activity is currently sheared eastward from the surface low pressure center due to strong upper westeriles on the south side of the upper vortex.

Atmospheric Outlook for the Forecast Period...A 996 mb frontal cyclone currently over eastern Canada and blocking upper ridge (marked by blue H in the above atmospheric features chart)...pumped up by warm air advection ahead of the frontal cyclone...are both passing north of the surface low. Intensifying upper convergence on the east side of the blocking upper ridge has caused the surface ridge offshore of Newfoundland to also intensify to 1032 mb. The 1018 mb surface ridge behind the frontal cyclone (currently over the eastern US) will soon merge with the 1032 mb surface ridge...creating a blocking surface ridge north of the surface low. The expanding blocking upper ridge will push the upper vortex southwestward toward the surface low...causing the surface low to whirl counter-clockwise around the upper vortex while it becomes trapped south of the blocking surface ridge. Afterwards...beyond 48 hours...the surface low will accelerate northward on the west side of the blocking surface ridge and in advance of the next frontal cyclone approaching from the United States. If the forecast below verifies...Bermuda will be affected by a surface low evolving into a subtropical cyclone in the next 36 hours...followed by a pass very close to Massachusetts and the US New England coast by 96 hours. It should be noted that by 96 hours this system should be transitioning to non-tropical as it interacts with upper divergence on the east side of the upper trough associated with the incoming frontal cyclone.

Thermodynamic Outlook for the Forecast Period...I forecast transition to a subtropical cyclone by 48 hours...when instability will be maximum as the surface low is closest to the center of the upper vortex...due to the cold core temperatures of the upper vortex positioned overhead of the warm 28 to 29 deg C waters...and with the surface low being shielded from wind shear by the overhead upper vortex. I then forecast transition to fully tropical status beyond 48 hours as the surface low accelerates northward away from the upper vortex and below warm core upper ridging to amplify due to warm air advection in advance of the frontal cyclone forecast to approach from the US by that time. By 96 hours this system should be transitioning to non-tropical while crossing the 26 deg C isotherm into cooler waters and interacting with upper divergence on the east side of the upper trough associated with said frontal cyclone.

24 Hr Forecast (0000Z Aug 22)...Surface low centered just south of Bermuda at 31.5N-65W

48 Hr Forecast (0000Z Aug 23)...45 mph max sustained wind subtropical storm centered west-northwest of Bermuda at 33N-67.5W

72 Hr Forecast (0000Z Aug 24)...50 mph max sustsained wind tropical storm centered offshore of the eastern United States at 35N-69.5W

96 Hr Forecast (0000Z Aug 25)...50 mph max sustained wind tropical storm centered just offshore of Massachusetts at 40.5N-69.5W...beginning to transition into a non-tropical remnant low

...SPECIAL FEATURE...TROPICAL WAVE EMERGING FROM AFRICA...
Current Prognosis...Baesd on the 0000Z infrared satellite image from Meteosat-9...I estimate that a semi-organized tropical wave axis featuring an expansive field of strong thunderstorms is nearing the west coast of Africa and hence will soon enter the eastern tropical Atlantic while loacted at 14W longitude. The tropical wave is moving into a region of moist air...warm 28 to 29 sea-surface temperatures...and favorable low vertical wind shear beneath an upper ridge covering the eastern tropical Atlantic. Therefore tropical cyclone formation from this tropical wave is high.

Atmospheric Outlook for the Forecast Period...This system will be steered westward by the 1032 to 1027 mb Atlantic surface ridge marked in the above atmospheric features chart. It will be located below a favorable eastern tropical Atlantic upper ridge (marked by blue zig-zag line in the lower-right corner of the above atmospheric features chart) thru the forecast period.

Thermodynamic Outlook for the Forecast Period...This system will be tracking over 28 to 29 deg C sea surface temperatures thru the forecast period. Their is some uncertainty as to whether or not this system will ingest the strip of unfavorable dry Saharan air seen in the bottom-center of the above thermodynamics chart. Given that Danny has done well against this dry air in a low shear environemnt and that this tropical wave will be staying in a low shear environment thru the forecast period...my current assumption is that dry air will not be a problem for this tropical wave.

24 Hr Forecast (0000Z Aug 22)...Tropical wave axis southeast of the Cape Verde Islands at 19W longitude

48 Hr Forecast (0000Z Aug 23)...Tropical wave organizing into tropical low south of the Cape Verde Islands centered at 11.5N-25W

72 Hr Forecast (0000Z Aug 24)...Well-organized tropical low centered at 11.5N-29W

96 Hr Forecast (0000Z Aug 25)...45 mph maximum sustained wind tropical storm centered at 12N-34W

120 Hr Forecast (0000Z Aug 26)...60 mph maximum sustained wind tropical storm centered at 13N-39W

2015 Atlantic Hurricane Season Birdseye Discussion #62

By: NCHurricane2009, 3:55 AM GMT on August 20, 2015

...THURSDAY AUGUST 20 12:00 AM EDT...
Tropical Storm Danny continues to chug westward across the central Atlantic tropics and could pose a threat to the northern Lesser Antilles and northeastern Caribbean islands within the next few days. See special feature section below for additional details on Danny.

Computer models continue to suggest there is potential for vigorous tropical waves to the east of Danny to also develop. Satellite imagery and lastest surface analysis from the National Hurricane Center TAFB suggests one such vigorous tropical wave is in the vicinity of the Cape Verde Islands...but is currently not showing signs of development while lacking organization. Satellite also shows a second such tropical wave is about to emerge from the west coast of Africa...and this particular wave is better organized and will be watched carefully as it rolls into the Atlantic.

Elsewhere...an upper vortex and 1016 mb surface low just north of Bermuda are what are left of an old frontal boundary system that emerged from the eastern United States on August 13. Over the next 24 hours...the 1016 mb surface low is forecast to dissipate while another one supported by upper divergence at the boundary of the upper vortex forms southwest of Bermuda with potential for subtropical or tropical cyclone development. Given that this surface low will already start out non-frontal...the warm mid-August sea-surface temperatures in this area...and the fact the cold core temperatures of the upper vortex may further aid in the instability...I believe there is a high chance that a subtropical or tropical storm will form in the western Atlantic within the next five days and have upgraded this area to a special feature on this blog. See second special feature section below for additional details on this situation. Of note...this area has been introduced into the National Hurricane Center 5-day tropical weather outlook within the last 24 hours and has already been given a moderate chance of development in the outlook.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1920Z-released WPC analysis.

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL STORM DANNY...
Current Prognosis...After strengthening yesterday...today the tropical storm leveled off in intensity while struggling with dry air ingestion. The most recent satellite frames tonight however show that strong thunderstorm activity has re-developed over and near the center of circulation. Satellite showed that the center of Danny passed over 11.5N-42.5W as of 0000Z earlier this evening which lines up very close to my previous track forecast.

Atmospheric Outlook for the Forecast Period...The eastern tropical Atlantic is covered by a favorable upper ridge as marked by a blue-zig-zag line in the bottom-right of the above atmospheric features chart. Meanwhile a TUTT (Tropical Upper Tropospheric Trough) consisting of four upper vortices (marked by four blue Ls) is located to the north of this upper ridge. The 1022 to 1025 mb Atlantic surface ridge marked in the atmospheric features chart will steer Danny west to west-northwest thru the forecast period...with the tropical storm intially taking advantage of favrable upper winds below the upper ridge but then reaching unfavorable southwesterly shear on the south side of the TUTT by the end of the forecast period.

Thermodynamic Outlook for the Forecast Period...Danny will be tracking over favorable 28 to 29 deg C waters through the forecast period...but will continue to track westward into dry Saharan air seen in the bottom-center of the above thermodynamics chart.


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

24 Hr Forecast (0000Z Aug 21)...65 mph max sustained wind tropical storm centered at 12.5N-46W

48 Hr Forecast (0000Z Aug 22)...80 mph max sustained wind hurricane centered at 13.5N-49W

72 Hr Forecast (0000Z Aug 23)...85 mph max sustained wind hurricane centered at 14.5N-52.5W

96 Hr Forecast (0000Z Aug 24)...70 mph max sustsained wind tropical storm centered at 15N-57.5W

120 Hr Forecast (0000Z Aug 25)...65 mph max sustained wind tropical storm moving across northern Lesser Antilles...centered at 16N-62.5W

Track Forecast...Track forecast is a copy-paste of my previous given that the previous forecast continues to do well as noted in the above current prognosis section.

Intensity Forecast...Holding on to my previous intensity forecast which shows Danny gradually strengthening into an 85 mph max sustained wind hurricane. The key word here is "gradual" because the amount of dry Saharan air immediately adjacent to Danny in the above thermodynamics chart suggests that rapid strengthening is not as likely. The weakening shown at the end of the forecast period is due to the increasing vertical shear Danny is forecast to reach as noted at the end of the above atmospheric outlook section.

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track...with a slight growth of this radius to account for the fact that Danny is expected to strengthen further. If the above forecast holds...the Lesser Antilles are about five days away from getting a direct strike from Danny...and perhaps Puerto Rico and the Virgin Islands are about six days away from a strike from Danny. Therefore these areas should continue to monitor the progress of this tropical storm.

...SPECIAL FEATURE...WESTERN ATLANTIC SUBTROPICAL DISTURBANCE...
Current Prognosis...An upper vortex is currently located just north of Bermuda and is marked by a blue L in the above atmospheric features chart. Split flow upper divergence between the south side of the upper vortex and east side of an upper ridge over the eastern US (marked by blue-zig-zag line) is supporting an extensive area of showers and thunderstorms southwest of and south of Bermuda. A surface low is forecast to form with the support of this upper divergence within the next 24 hours.

Atmospheric Outlook for the Forecast Period...As the surface low forms southwest of Bermuda in the next 24 hours...the aforementioned eastern US upper ridge as well as the 996 mb frontal cyclone currently over the north-central US will pass to the north. Warm air advection ahead of the frontal cyclone will amplify the upper ridge into a blocking upper ridge...with intensifying upper convergence on the east side of the blocking upper ridge causing the 1024 mb surface ridge offshore of Newfoundland to also intensify. The 1019 mb surface ridge behind the frontal cyclone (currently over the western US) will also quickly merge with the 1024 mb surface ridge...creating a blocking surface ridge north of the surface low. The expanding blocking upper ridge will push the upper vortex southwestward toward the surface low...causing the surface low to whirl counter-clockwise around the upper vortex while it becomes trapped south of the blocking surface ridge. Afterwards...beyond 72 hours...the surface low will accelerate northward on the west side of the blocking surface ridge and in advance of the next frontal cyclone approaching from the United States. If the forecast below verifies...Bermuda will be affected by a surface low evolving into a subtropical cyclone in the next 48 hours...followed by a pass very close to Massachusetts and the US New England coast by 120 hours. It should be noted that by 120 hours this system should be transitioning to non-tropical as it interacts with upper divergence on the east side of the upper trough associated with the incoming frontal cyclone.

Thermodynamic Outlook for the Forecast Period...I forecast transition to a subtropical cyclone by 72 hours...when instability will be maximum as the surface low is closest to the center of the upper vortex...due to the cold core temperatures of the upper vortex positioned overhead of the warm 28 to 29 deg C waters...and with the surface low being shielded from wind shear by the overhead upper vortex. I then forecast transition to fully tropical status beyond 72 hours as the surface low accelerates northward away from the upper vortex and below warm core upper ridging to amplify due to warm air advection in advance of the frontal cyclone forecast to approach from the US by that time. By 120 hours this system should be transitioning to non-tropical while crossing the 26 deg C isotherm into cooler waters and interacting with upper divergence on the east side of the upper trough associated with said frontal cyclone.

24 Hr Forecast (0000Z Aug 21)...Weak surface low centered southwest of Bermuda at 30N-67.5W

48 Hr Forecast (0000Z Aug 22)...Surface low centered just southwest of Bermuda at 31.5N-65.5W

72 Hr Forecast (0000Z Aug 23)...45 mph max sustained wind subtropical storm centered west-northwest of Bermuda at 33N-67.5W

96 Hr Forecast (0000Z Aug 24)...50 mph max sustsained wind tropical storm centered offshore of the eastern United States at 35N-69.5W

120 Hr Forecast (0000Z Aug 25)...50 mph max sustained wind tropical storm centered just offshore of Massachusetts at 40.5N-69.5W

2015 Atlantic Hurricane Season Birdseye Discussion #61

By: NCHurricane2009, 5:54 AM GMT on August 19, 2015

...WEDNESDAY AUGUST 19 2015 1:55 AM EDT...
Tropical wave Invest 96-L midway between the Lesser Antilles and Cape Verde Islands strengthened to tropical depression four this past morning...and has further strengthened to Tropical Storm Danny as of this past afternoon. Interests in the Lesser Antilles and eastern Caribbean Sea should monitor the progress of Danny as the storm is likely to continue strengthening while approaching the area. See special feature section for additional details on Danny.

Computer models suggest there is potential for vigorous tropical waves to the east of Danny to also develop. Satellite imagery and lastest surface analysis from the National Hurricane Center TAFB suggests one such vigorous tropical wave is in the vicinity of the Cape Verde Islands...but is currently not showing signs of development while lacking organization.

Elsewhere...the surface trough over the Bahamas has dissipated.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL STORM DANNY...
Current Prognosis...As of the lastest 11 PM EDT National Hurricane Center advisory...Tropical Storm Danny was assessed to be steadily strengthening with maximum sustained winds already climbing to 50 mph. Satellite animation showed that the center of Danny passed over 11N-38W as of 0000Z earlier this evening which lines up exactly with my previous track forecast as far as longitude...but is 1N latitude further north from my previous track forecast. Danny currently has the appearance of a tropical storm that continues to strengthen while featuring a circular core of thunderstorms and spiral band wrapped around while taking advantage of low shear and enhanced outflow beneath an upper ridge in the eastern tropical Atlantic (marked by blue-zig-zag line in the lower-right corner of the above atmospheric features chart) and 28 to 29 deg C sea surface temperatures.

Atmospheric Outlook for the Forecast Period...The eastern tropical Atlantic is covered by a favorable upper ridge as marked by a blue-zig-zag line in the bottom-right of the above atmospheric features chart. Meanwhile a pair of upper vortices in the western Atlantic (marked by two blue Ls) will consolidate into a TUTT (Tropical Upper Tropospheric Trough) to the north of this upper ridge. Because Danny is expected to stay south of 20N thru the forecast period...it is likely to take advantage of favrable upper winds below the upper ridge and stay away from unfavorable westerly shear associated with the TUTT. What will keep Danny south of 20N and steer it west is the 1025 mb Atlantic surface ridge marked in the above atmospheric features chart.

Thermodynamic Outlook for the Forecast Period...Danny will be tracking over favorable 28 to 29 deg C waters through the forecast period...but will track westward into dry Saharan air seen in the bottom-center of the above thermodynamics chart. This dry air apperas to the only factor that could negatively affect the strength of Danny during the forecast period.


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

24 Hr Forecast (0000Z Aug 20)...65 mph max sustained wind tropical storm centered at 12N-42W

48 Hr Forecast (0000Z Aug 21)...75 mph max sustained wind hurricane centered at 12.5N-46W

72 Hr Forecast (0000Z Aug 22)...85 mph max sustained wind hurricane centered at 13.5N-49W

96 Hr Forecast (0000Z Aug 23)...85 mph max sustained wind hurricane centered at 14.5N-52.5W

120 Hr Forecast (0000Z Aug 24)...85 mph max sustsained wind hurricane centered at 15N-57.5W

Track Forecast...Track forecast is a copy-paste of my previous with a northward adjustment to account for the fact that Danny is about 1 degree latitude further north than I previously expected as noted in the above current prognosis section. My track forecast is a bit faster to the west than the latest NHC track forecast.

Intensity Forecast...Danny is currently stronger than my previous intensity forecast...and the storm will be in favorable low shear...have good upper outflow...and be over warm sea surface temperatures thru the forecast period. Therefore I have bumped up the intensity forecast. However with such a well-defined Saharan air layer just to the northwest of Danny in the above thermodynamics chart...my intensity forecast is not as strong as the NHC's...but instead I split the difference between my previous intensity forecsat and the current NHC intensity forecast. Of note...if the above intensity forecast holds...this will be the first hurricane of the 2015 Atlantic season.

Impact Forecast...Impact swath in the above forecast graphic is an extrapolation of the 11 PM EDT NHC tropical storm wind radius along my forecast track...with a slight growth of this radius to account for the fact that Danny is expected to strengthen further. If the above forecast holds...the Lesser Antilles are about six days away from getting a direct strike from Danny and interests in the Lesser Antilles and eastern Caribbean should monitor Danny over the next few days.

2015 Atlantic Hurricane Season Birdseye Discussion #60

By: NCHurricane2009, 4:43 AM GMT on August 18, 2015

...TUESDAY AUGUST 18 2015 12:45 AM EDT...
Tropical wave Invest 96-L in the eastern tropical Atlantic located southwest of the Cape Verde Islands continues to slowly organize and is likely to become the next tropical depression or storm of the 2015 Atlantic Hurricane Season. See special feature section below for additional details on 96-L.

Computer models suggest there is potential for vigorous tropical waves to the east of 96-L to also develop. Satellite imagery suggests one such vigorous tropical wave with well-defined rotation has left the west coast of Africa and is currently just south of the Cape Verde Islands...but is currently not showing signs of development while lacking concentrated thunderstorm activity.

Elsewhere...a surface trough has developed from yesterday's thunderstorm cluster located over the Dominican Republic...Puerto Rico...and adjacent western Atlantic waters. This surface trough is already moving westward across the Bahamas and will continue westward toward south Florida and into the Gulf of Mexico while steered by the 1021 mb surface ridge that has recently emerged from the southeastern US. Upper-level winds could become more favorable for this surface trough while an upper ridge offshore of the southeastern US and eastern Gulf of Mexico solidifies above the surface trough (this upper ridge is currently marked with a blue H on the north coast of the Yucatan peninsula of southeastern Mexico in the atmospheric features chart below). So far this surface trough has not shown signs of development while losing thunderstorm activity over the last 24 hours...and none of the computer models currently forecast this surface trough to develop.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 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. Surface troughs labeled with TW indicates the trough is a tropical wave whose origin is from the mid-level African Easterly Jet. Ls indicate surface lows, Hs indicate surface highs.

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL WAVE INVEST 96-L...
Current Prognosis...As of 1800Z this afternoon...the National Hurricane Center TAFB analyzed that the surface low pressure spin of the tropical wave southwest of the Cape Verde Islands had a pressure of 1010 mb. Satellite animation suggests the surface low pressure center has traveled from 9.5N-32W at 1800Z to 9.5N-33.5W as of 0000Z. This is slightly south and further west than where 96-L was predicted to be 24 hours ago. The thunderstorm activity has not become any better organized relative to 24 hours ago...but remains well organized such that tropical cyclone formation is possible at any time.

Atmospheric Outlook for the Forecast Period...The eastern tropical Atlantic is covered by a favorable upper ridge as marked by a blue-zig-zag line in the bottom-right of the above atmospheric features chart. Meanwhile a TUTT (Tropical Upper Troposheric Trough) is present from eastern Cuba and extends to the central Atlantic waters just west of the Azores marked by a pair of blue Ls and blue-dashed line in the atmospheric features chart. A fragment of an upper trough over the eastern US has also emerged into the western Atlantic as an upper vortex (marked by blue L) located just east of North Carolina which will merge with and re-enforce the TUTT. Because Invest 96-L is expected to stay south of 20N thru the forecast period...it is likely to take advantage of favrable upper winds below the upper ridge and stay away from unfavorable westerly shear associated with the TUTT. What will keep 96-L south of 20N and steer it west is the strong 1027 mb Atlantic surface ridge marked in the above atmospheric features chart. The latest CMC and GFS model runs continue to suggest 96-L will have a slow westward pace due to the tug of the vigorous tropical waves to the east which are currently entering the Atlantic from the west coast of Africa...while the Euro (ECMWF) shows a faster westward track while showing less entaglement with these tropical waves. Based on the above current prognosis section which states that 96-L is moving faster to the west than previously anticipated...I have adjusted my track foreast below to be faster to the west and lean more toward the Euro solution. This may mean that 96-L may no longer get entangled and compete for low-level inflow with the neighboring tropical waves to the east...but I am still inclined to show a conservative intensity forecast due to the less favorable thermodynamic conditions that lie ahead (as noted in the thermodynamic section below).

Thermodynamic Outlook for the Forecast Period...96-L is currently over very favorable 29 to 30 deg C waters...but will track westward into dry Saharan and slightly cooler (but still favorable) 28 deg C waters seen in the bottom-center of the above thermodynamic chart.

24 Hr Forecast (0000Z Aug 19)...35 mph max sustained wind tropical depression centered at 10N-38W

48 Hr Forecast (0000Z Aug 20)...45 mph max sustained wind tropical storm centered at 10.5N-42W

72 Hr Forecast (0000Z Aug 21)...50 mph max sustained wind tropical storm centered at 11N-46W

96 Hr Forecast (0000Z Aug 22)...60 mph max sustained wind tropical storm centered at 12N-49W

120 Hr Forecast (0000Z Aug 23)...65 mph max sustained wind tropical storm centered at 13N-52.5W

2015 Atlantic Hurricane Season Birdseye Discussion #59

By: NCHurricane2009, 9:36 PM GMT on August 16, 2015

...SUNDAY AUGUST 16 2015 5:36 PM EDT...
Tropical wave Invest 96-L in the eastern tropical Atlantic located south-southwest of the Cape Verde Islands...mentioned in special update #58A... continues to rapidly organize this afternoon and therefore is upgraded to a special feature on this blog. See special feature section below for additional details on this developing situation.

Satellite imagery suggests another vigorous tropical wave is entering the eastern tropical Atlantic to the east of Invest 96-L. Computer models also suggest that this tropical wave has potential to develop and therefore this tropical wave bears watching.

Elsewhere...upper-level divergence on the east side of a weakening upper trough north of the Dominican Republic (part of the Tropical Upper Tropospheric Trough...or TUTT...mentioned in the special feature section below)...is interacting with surface convergence at the north end of a tropical wave moving through the eastern Caribbean which has resulted in a signficant increase in showers and thunderstorms north of Puerto Rico this afternoon. If a surface trough were to develop in these thunderstorms...it will generally track west-northwest across the Bahamas...south Florida...and into the eastern Gulf of Mexico while steered by the current 1023 mb and 1029 mb eastern US and Atlantic surface ridges marked in the atmospheric featuers chart below. Upper-level winds will become more favorable for such a surface trough as the weakening upper trough north of the Dominican Republic will move southwest into the Caribbean while an upper ridge offshore of the southeastern US and eastern Gulf of Mexico solidifies above the surface trough (this upper ridge is currently marked with a blue H offshore of the southeastern US in the atmospheric features chart below). Therefore although none of the computer models currently develop the disturbance north of Puerto Rico...it does also bear watching over the next few days.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1200Z and 1323Z-released WPC analysis.

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

...SPECIAL FEATURE...TROPICAL WAVE INVEST 96-L...
Current Prognosis...As of 1200Z this afternoon...the National Hurricane Center TAFB analyzed that the surface low pressure spin of the tropical wave south-southwest of the Cape Verde Islands had a pressure of 1011 mb. Satellite animation suggests the surface low pressure center has traveled from 10N-26.8W at 1200Z to 10N-27.5W as of 1800Z. The thunderstorm activity continues to organize into spiral bands around the surface low while this system takes advantage of very favroable 30 deg C sea surface temperatures as well as low shear and enhanced upper outflow beneath an upper ridge marked by a blue-zig-zag in the lower-right corner of the atmospheric featuers chart above.

Atmospheric Outlook for the Forecast Period...The eastern tropical Atlantic is covered by a favorable upper ridge as marked by a pair of blue-zig-zag lines in the bottom-center and bottom-right of the above atmospheric features chart...although a less favorable inverted upper trough is embedded in the upper ridge as marked by a blue dashed line between the two blue-zig-zag lines. This inverted upper trough is forecast to dissipate while the upper ridge solidifies. Meanwhile a TUTT (Tropical Upper Troposheric Trough) is present from just north of the Dominican Republic and extends to the central Atlantic as marked by a blue-dashed line and pair of blue Ls in the atmospheric features chart. Because Invest 96-L is expected to stay south of 20N thru the forecast period...it is likely to take advantage of favrable upper winds below the solidifying upper ridge and stay away from unfavorable westerly shear associated with the TUTT. What will keep 96-L south of 20N and steer it west is the strong 1029 mb Atlantic surface ridge marked in the above atmospheric features chart. The westward pace noted in the above current prognosis section is a bit on the slow side...and current computer model runs suggest the westward pace of 96-L will remain slow due to the tug of the vigorous tropical wave to the east which is currently entering the Atlantic from the west coast of Africa. Competition for low-level inflow from the neighboring tropical wave and slightly less favorable thermodynamic conditions that lies ahead (as noted in the thermodynamic section below) cause me to show a gradual instead of rapid development in my intensity forecast below.

Thermodynamic Outlook for the Forecast Period...Tropical waves 93-L and 94-L in late July and early August failed to develop due to the dry Saharan air layer which is still present over parts of the tropical Atlantic. A comparison of the above thermodynamics chart to late July and early August suggests more saharan air present than during the time of 93-L but less saharan air than during the time of 94-L. Given that 96-L is rapidly organizing today...and that the thermodynamic environment is generally more unstable given the warmer sea-surface temperatures relative to late July and early August...I prefer to make 96-L a special feature on this blog and forecast it to develop into a tropical cyclone. 96-L is currently over very favorable 30 deg C waters...but will track westward into dry Saharan and slightly cooler (but still favorable) 28 deg C waters seen in the bottom-center of the above thermodynamic chart. The slightly less favorable dry air and cooler waters that lies ahead is partly why I forecast a gradual rather than rapid development of 96-L as noted at the end of the above atmospheric outlook section.

24 Hr Forecast (1800Z Aug 17)...35 mph max sustained wind tropical depression centered at 10.5N-30.3W

48 Hr Forecast (1800Z Aug 18)...45 mph max sustained wind tropical storm centered at 11N-34W

72 Hr Forecast (1800Z Aug 19)...50 mph max sustained wind tropical storm centered at 11.5N-37.5W

96 Hr Forecast (1800Z Aug 20)...60 mph max sustained wind tropical storm centered at 12N-40W

120 Hr Forecast (1800Z Aug 21)...65 mph max sustained wind tropical storm centered at 12.5N-43.5W

2015 Atlantic Hurricane Season Birdseye Discussion #58A (Special Update)

By: NCHurricane2009, 2:21 PM GMT on August 16, 2015

...SUNDAY AUGUST 16 2015 10:22 AM EDT...
A well-organized tropical wave with a cloud swirl has rolled off the west coast of Africa within the last couple of days. This morning while located south-southwest of the Cape Verde Islands...its associated thunderstorm activity has increased and it has been introduced into the National Hurricane Center Tropical Weather Outlook. In addition...the tropical wave has been upgraded to disturbance Invest 96-L on the Naval Research Laboratory (NRL) site of the US Navy. Therefore I am resuming daily updates on the Atlantic tropics on this blog while in the process of deciding whether or not to consider 96-L as a special feature in my next blog update to be released either late this morning or early this afternoon.

2015 Atlantic Hurricane Season Birdseye Discussion #58

By: NCHurricane2009, 2:05 AM GMT on August 08, 2015

...FRIDAY AUGUST 7 2015 10:05 PM EDT...
All remains quiet in the Atlantic tropics. I am ceasing daily updates on this blog until the threat of tropical cyclone activity returns to the Atlantic basin.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

2015 Atlantic Hurricane Season Birdseye Discussion #57

By: NCHurricane2009, 1:32 AM GMT on August 07, 2015

...THURSDAY AUGUST 6 2015 9:35 PM EDT...
All is quiet in the Atlantic tropics...

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1920Z-released WPC analysis.

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

2015 Atlantic Hurricane Season Birdseye Discussion #56

By: NCHurricane2009, 12:04 AM GMT on August 06, 2015

...WEDNESDAY AUGUST 5 2015 8:04 PM EDT...
Tropical low Invest 95-L has dissipated just off the coast of North Carolina.

Elsewhere...the vigorous and well-organized tropical wave in the eastern tropical Atlantic has left behind a 1010 mb tropical low just southeast of the Cape Verde Islands. None of the computer models forecast this tropical low to develop...perhaps due to the extensive amount of dry Saharan air seen in the bottom-center of the thermodynamics chart below. In fact...those most recent satellite frames show thunderstorm activity decreasing as the circulation begins to ingest the dry air...and therefore tropical cyclone formation is not expected.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

This chart is generated based on surface analysis from the National Hurricane Center TAFB at 1800Z and 1937Z-released WPC analysis.

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

2015 Atlantic Hurricane Season Birdseye Discussion #55

By: NCHurricane2009, 11:53 PM GMT on August 04, 2015

...TUESDAY AUGUST 4 2015 8:00 PM EDT...
The surface center of Invest 95-L has continued northeastward from coastal Georgia and is currently moving along the Carolina coast. As expected...the upper ridge centered over eastern Texas has bridged with the western Atlantic upper ridge (both marked by blue Hs in the atmospheric features chart below)...which earlier this afternoon resulted in a reduction of unfavorable vertical shear and nearly caused 95-L to be upgraded to a tropical cyclone. Tropical cyclone formation is now becoming unlikely as the most recent satellite frames show 95-L becoming less organized as it moves into hostile westerly shear north of both aforementioned upper ridges...and as 95-L in the next 24 hours will become absorbed by the cold front coming in from the Ohio Valley.

A vigorous and well-organized tropical wave has entered the eastern tropical Atlantic from western Africa. None of the computer models forecast this tropical wave to develop...perhaps due to the extensive amount of dry Saharan air seen in the bottom-center of the thermodynamics chart below. However if this tropical wave shows signs of organizing into a tropical cyclone prior to reacing this dry air...I will upgrade this tropical wave to a special feature on this blog.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

2015 Atlantic Hurricane Season Birdseye Discussion #54

By: NCHurricane2009, 1:30 AM GMT on August 04, 2015

...MONDAY AUGUST 3 2015 9:30 PM EDT...
The surface center of Invest 95-L has moved northeastward from Florida and into coastal Georgia...but its south side continues to produce rain over saturated northern Florida grounds and therefore flooding remains the immediate threat from 95-L. 95-L is expected to continue northeast along the SE US coast over the next 48 hours in the flow between the 1025 mb Atlantic ridge and 997 mb east Canada surface low...with the cold front currently over the Ohio Valley moving offshore and absorbing 95-L by 48 hours. An upper ridge centered over eastern Texas (marked by blue H in the atmospheric features chart below) is shearing thunderstorms southwestward from the surface center of 95-L. However in the next 24 hours the east Texas upper ridge will bridge with the western Atlantic upper ridge (also marked by blue H) which will lessen the unfavorable shear over 95-L...leaving the possibility of 95-L evolving into a short-lived tropical cyclone over or just offshore of the SE US coast prior to 48 hours. Will upgrade 95-L to a special feature on this blog if this starts to occur.

A vigorous and well-organized tropical wave is currently located over western Africa and will enter the eastern tropical Atlantic in 24 to 48 hours (1 to 2 days). However with plenty of dry Saharan air seen in the bottom-center of the thermodynamics chart below...its eventual development into a tropical cyclone is not likely.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

2015 Atlantic Hurricane Season Birdseye Discussion #53

By: NCHurricane2009, 3:54 AM GMT on August 03, 2015

...SUNDAY AUGUST 2 2015 11:55 PM EDT...
A cold front has been driven into the western Atlantic and northern Gulf of Mexico by what is currently the broad 996 mb surface low over eastern Canada. This is the same front that absorbed last week's frontal but tropical-like disturbance that sat over northern Florida during previous disucssions #45 to #51. Today...this front has generated yet another tropical-like circulation currently parked over northern Florida which has gained introduction in the National Hurricane Center tropical weather outlook and has been upgraded to Invest 95-L on the Naval Research Laboratory site of the US Navy.

Invest 95-L is producing heavy rains over northern Florida...an area which is already saturated by last week's tropical-like ciruclation and therefore flooding over northern Florida is the immediate threat from 95-L. An upper ridge centered over the northern Gulf (marked by blue H in the atmospheric features chart below) is shearing thunderstorms southwestward from the surface center of 95-L. Some of these thunderstorms are located offshore in the eastern Gulf of Mexico and closer to a more favorable low shear and upper outflow environment closer to the center of the upper ridge. However visible satellite imagery...850 mb vorticity analysis from CIMSS...and surface analysis from TAFB are not showing a second circulation in these thunderstorms. Meanwhile the circulation of 95-L is expected to move northeast along the SE US coast over the next 72 hours in the flow between the 1023 mb Atlantic ridge and 996 mb east Canada surface low...with the cold front currently producing severe thunderstorms over Michigan moving offshore and absorbing 95-L by 72 hours. By 48 hours the northern Gulf upper ridge will bridge with the western Atlantic upper ridge (marked by blue-zig-zag line) which will lessen the unfavorable shear over 95-L...leaving the possibility of 95-L evolving into a short-lived tropical cyclone over or just offshore of the SE US coast prior to 72 hours. Will upgrade 95-L to a special feature on this blog if this starts to occur.

A vigorous and well-organized tropical wave is currently located over western Africa and will enter the eastern tropical Atlantic in 48 to 72 hours (2 to 3 days). Its potential for development will depend on how much the tropical waves ahead of it moisten out the dry Saharan air layer presently seen in the bottom-center of the thermodynamics chart below. So far the dry Saharan air layer has not weakened...and in fact is stronger relative to 24 hours ago and therefore it is less likely this tropical wave will develop when it enters the Atlantic.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

2015 Atlantic Hurricane Season Birdseye Discussion #52

By: NCHurricane2009, 1:21 AM GMT on August 02, 2015

...SATURDAY AUGUST 1 2015 9:22 PM EDT...
A vigorous tropical wave is currently located over west-central Africa and will enter the eastern tropical Atlantic in 96 hours (4 days). Its potential for development will depend on how much the tropical waves ahead of it moisten out the dry Saharan air layer presently seen in the bottom-center of the thermodynamics chart below. Currently the GFS computer model is the only model that suggests potential for development of this tropical wave when it enters the eastern tropical Atlantic.

It is quiet elsewhere in the Atlantic tropics.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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

2015 Atlantic Hurricane Season Birdseye Discussion #51

By: NCHurricane2009, 2:18 AM GMT on August 01, 2015

...FRIDAY JULY 31 2015 10:18 PM EDT...
The 1011 mb surface low offshore of the southeastern US is located just east of the North Carolina Outer Banks and has become absorbed by the cold front driven by the 986 mb frontal cyclone over the eastern US and eastern Canada. Therefore tropical cyclone formation from the 1011 mb surface low is no longer possible.

Tropical surface low Invest 94-L currently located west-southwest of the Cape Verde Islands in the eastern tropical Atlantic continues westward. Even though Invest 94-L is under a favorable low shear and good upper outflow environment under an upper ridge (marked by blue zig-zag line in the lower-right corner of the atmospheric features chart)...tropical cyclone formation from 94-L is not expected as its thunderstorms continue to weaken as its circulation is ingesting dry saharan air which is well-defined in the bottom-center of the thermodynamics chart below.

...ATMOSPHERIC FEATURES BIRDSEYE CHART...

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

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

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

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

...THERMODYNAMICS BIRDSEYE CHART...

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

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


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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