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BIRDSEYE VIEW POSTS

Since 2012 on the now retired Weather Underground blogs, I have been posting annotated "birdseye view" charts of the Atlantic basin, with a detailed explanation and forecasting that references the chart. From there you may know me as "NCHurricane2009." While I now do these "birdseye view" posts here, I will continue to do comments at Yale Climate Connections via Disqus where the former Weather Underground community has moved to. Feel free to reply to me there, at my Disqus feed at this link, or via e-mail at IOHurricanes@outlook.com 

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MY 2023 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #90

*******Note that forecast and outlooks in this post are NOT the official forecast from the National Hurricane Center (NHC). They are my own detailed views on the Atlantic tropics based on current observations and latest computer model runs. As such do not make decisions based on my posts...consult news media...watches and warnings from your local weather office...and any evacuation orders issued by local governments to make the most informed and best decisions. Visit the NHC website hurricanes.gov (hurricanes dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.*********


...UPDATE...TUESDAY OCTOBER 3 2023 4:41 PM EDT...

The birdseye view chart below has been updated to now include the surface analysis from 1800Z October 2 and upper level analysis from 1200Z October 2... which represents the setup of the atmosphere at the time I completed the forecasts in the full update below.


Concerning Philippe... the storm center continues to track more west and less north relative to previous forecasts which allowed the center to cross the northernmost Lesser Antilles overnight and this morning... and the northernmost Virgin Islands through this afternoon. This will now allow for periods of gusty winds... heavy rains... and coastal surf to extend as far west as the Virgin Islands and Puerto Rico for the rest of today and tonight.


...MONDAY OCTOBER 2 2023 8:40 PM EDT...


Note the usual surface analysis and upper air charts for the above birdseye view chart are still being assembled and will be released within the next several hours. This update is released now without those parts of the chart to ensure a timely release of this update.


Rina in the open central Atlantic has collapsed into a remnant low due to wind shear… see remnants of Rina for more information. Tropical Storm Philippe is impacting the Lesser Antilles tonight… and could later bring impacts across the mid-latitudes of the western Atlantic including for Bermuda and Atlantic Canada… see Philippe section below for more details.  Elsewhere watching for two possible tropical Atlantic areas of interest that could emerge in about 7 days as follows:

(1) As noted in the Philippe forecast discussion below… a large upper trough is forecast to pull the storm north across the west Atlantic by day 5. The tail end of this upper trough’s surface cold front could settle below a tropical upper ridge cell over the western Caribbean and Central America… with the upper ridge cell’s low shear and outflow favoring thunderstorm development. Therefore the tail end of the surface front could evolve into a western Caribbean and/or Central America tropical disturbance by day 7.

(2) Tropical development in the eastern Atlantic and offshore of Africa as of late has been suppressed by eastern Atlantic upper vorticity. However over the next 7 days the northeast fracture of the current northwest Atlantic upper trough is forecast to sweep the suppressing upper vorticity out of the region… and some global model runs suggest a tropical wave of low pressure to emerge from Africa may try to develop in the eastern Atlantic around day 7.


TROPICAL STORM PHILIPPE... While moving west-northwest and then northwest toward the surface ridge ridge weakness associated with the current oblong northwest Atlantic frontal low... the tropical storm has churned toward the northern Lesser Antilles with the center of circulation passing over Barbuda as of 6 PM EDT. The tropical storm remains disorganized as thunderstorms continue to be pulled southeast of the cloud swirl center by a wave of upper vorticity now positioned to the southeast. However the thunderstorm latent heat release has probably weakened the cool core wave of upper vorticity such that the thunderstorms have not been held back too far from the center... and instead of Philippe weakening it has held on to a strength of 50 mph maximum sustained winds. Going forward... Philippe will be turning north while interacting with the oblong northwest Atlantic frontal low and its associated upper trough. By 24 hours... even though the tropical storm will remain in an unfavorable westerly shear environment... it will also be under increased upper divergence between northwesterlies streaming into the wave of upper vorticity to the southeast and southwesterlies ahead of the upper trough. I assume Philippe will begin to intensify with the aid of the upper divergence at 24 hours. After 24 hours the upper trough splits into southwestern and northeastern halves... with Philippe through day 5 interacting with the southwestern upper trough. The southwestern upper trough will become increasingly amplified due to ongoing amplified upper ridging over eastern North America... which will gradually reduce the westerly shear over Philippe and hence allow Philippe to intensify further. The latest model data suggests enough amplification of the eastern North America upper ridging to allow the southwestern upper trough to retrograde westward away from Philippe... meaning even lower shear over the storm. Moreover the convergence zone of the northeastern upper trough produces a surface ridge north of Philippe... the combo of the surface ridge and the retrograding southwestern upper trough forces me to suggest a west slant to Philippe's northward track through 72 hours. And with the lower shear forecast... I have raised the intensity forecast to indicate a category 2 hurricane by 72 hours. By 96 hours... an amplified central North America upper trough and its strong surface frontal cyclone finally have enough oomph to break through the eastern North America upper ridge and merge with the southwestern upper trough... making a lengthy northwest-southeast tilted upper trough that moves toward Philippe. I slow the intensification rate from 72 to 96 hours due to potentially increasing shear from the nearing lengthy upper trough... followed by a notable margin of weakening from 96 to 120 hours from a one-two punch of cooled sea surface temperatures caused by the August-September western Atlantic hurricanes (Franklin... Lee... Idalia) and a jump in southerly shear as the tilted lengthy upper trough digs into the south side of Philippe. After 120 hours and while moving over cooler water… Philippe has potential to transition into a strong northwestern Atlantic non-tropical frontal cyclone supported by the tremendous divergence zone of the tilted upper trough.


Regarding impact to land areas:

(1) For the northern Lesser Antilles… expect periods of gusty winds and coastal surf over the next 24 hours. Because of the storm’s track… the thunderstorms that are pushed southeast of the center are beginning to overspread all of the Lesser Antilles island chain… periods of heavy rainfall can also be expected across the islands over the next 24 hours.

(2) Per the above forecast discussion… the atmosphere is now setting up to potentially allow Philippe to barrel north into Bermuda by Thursday and Friday as a potentially strong hurricane. Interests here should monitor the progress of Philippe in the days ahead.

(3) If in fact Philippe moves into the northwest Atlantic… a round of coastal surf can be expected for the northeastern US and Atlantic Canada shores by this weekend. Atlantic Canada could also see more direct impacts such as gusty winds in the long range.

******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********

0 Hr Position (1800Z Oct 2)... 50 mph maximum sustained wind tropical storm centered just east of Barbuda at 17.6N-61.5W

IOH 24 Hr Forecast (1800Z Oct 3)... 60 mph maximum sustained wind tropical storm centered just north of the northern Lesser Antilles at 20N-62.5W

IOH 48 Hr Forecast (1800Z Oct 4)... 75 mph maximum sustained wind hurrricane centered in the western Atlantic at 23N-63.5W

IOH 72 Hr Forecast (1800Z Oct 5)... 100 mph maximum sustained wind hurricane centered south of Bermuda at 27.5N-65W

IOH 96 Hr Forecast (1800Z Oct 6)... 105 mph maximum sustained wind hurricane centered over Bermuda at 32N-65W

IOH 120 Hr Forecast (1800Z Oct 7)... 85 mph maximum sustained wind hurricane centered in the northwest Atlantic at 36N-65W

******National Hurricane Center (hurricanes.gov) official forecast as of 5 PM EDT***************************

5-Day Position (1800Z Oct 7)... 75 mph maximum sustained wind hurricane centered northeast of Bermuda at 35N-60W


REMNANTS OF RINA... The circulation of Rina in the open central Atlantic has curved northward and then northeastward in the flow ahead of the current oblong northwest Atlantic frontal low and its upper trough. Even though Rina has seen a notable uptick in thunderstorms thanks to boosting divergence on the southeast side of the upper trough… this happened too late as Rina weakened to a tropical depression and then remnant low without a well-defined center by Sunday night before getting a chance to take advantage of the upper divergence. Going forward… the remnants of Rina will be absorbed by the oblong frontal low… and this is my final statement on Rina on this blog as it is no longer a tropical cyclone.


...COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields(http://moe.met.fsu.edu/tcgengifs/).


1200Z (Oct 2) CMC Model Run...

**For Tropical Storm Philippe... while moving northwestward the storm center passes just northeast of the northern Lesser Antilles through 18 hours and reaches 20N-63W at 30 hours... subsequently accelerates north while becoming a hurricane and passes just east of Bermuda at 102 hours... center of hurricane located north-northeast of Bermuda at 35N-63W at 120 hours.

**Broad tropical low materialies over the western Caribbean... northern Honduras... Guatemala... Belize... and southeastern Mexico through 168 hours

**Tropical wave emerges from west coast of Africa at 114 hours and organizes into a broad tropical low that passes south of the Republic of Cabo Verde Islands through 168 hours.


1200Z (Oct 2) ECMWF Model Run...

**For Tropical Storm Philippe... while moving northwestward the storm center passes just northeast of the northern Lesser Antilles through 18 hours and reaches 20N-63.5W at 30 hours... subsequenlty accelerates north-northwest and then north-northeast with storm center passing just east of Bermuda at 102 hours... from 102 to 120 hours becomes entangled with a frontal cyclone developing to its immediate west with Philippe and the frontal cyclone located north of Bermuda by 120 hours.


1200Z (Oct 2) GFS Model Run...

**For Tropical Storm Philippe... while moving northwestward the storm center passes just northeast of the northern Lesser Antilles through 9 hours and reaches 20N-63W at 39 hours as a remnant low... reformation into a tropical cyclone suggested near 24N-62W at 75 hours... subsequently accelerates north-northeast while strengthening into a high-end tropical storm that reaches 32N-57.5W at 120 hours.

**Through 84 hours the northeastern half of the upper trough associated with the current oblong northwestern Atalntic frontal low becomes a very cold and amplified upper trough in the northeast Atlantic in response to amplified upper ridging over eastern North America... the northeastern half of the oblong frontal low intensifies into a frontal cyclone positioned just south of Iceland by 84 hours under the support of the eastern divergence zone of the northeast Atlantic upper trough while the upper trough's divergence zone also produces a new southern frontal cyclone near 45.5N-32.5W... the southern frontal cyclone and southern half of the upper trough evolve into a deep-layer cyclone with possible tropical characteristics near 45N-33W


1200Z (Oct 2) NAVGEM Model Run...

**For Tropical Storm Philippe... while moving northwestward the storm center passes just northeast of the northern Lesser Antilles through 12 hours and reaches 20N-63W at 30 hours... subsequently accelerates north-northeast while becoming a hurricane and reaches 31.8N-56W at 120 hours

**Tropical wave emerges from west coast of Africa at 132 hours with tropical cyclone formation suggested near 11N-20W at 168 hours

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