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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 #87

Updated: Sep 29, 2023

*******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...FRIDAY SEPTEMBER 29 2023 1:00 AM EDT...

The birdseye view chart below has been updated to now include the surface and upper-level analysis as of 0000Z September 28.


The tropical wave to the east-southeast of Philippe... tagged as area of interest #39 in the full update below... strengthened into Tropical Storm Rina as of 11 AM EDT September 28.


...THURSDAY SEPTEMBER 28 2023 2:15 AM EDT...

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


The primary focus for the Atlantic tropics at this time are a pair of central Atlantic tropical circulations now interacting with each other... see Tropical Storm Philippe and area of interest #39 section below for more details on the two circulations. See area of interest #41 section below for an update on the tropical wave that has been moving across the western Caribbean Sea... and see area of interest #42 section below for more information on possible subtropical development offshore of the eastern United States and northwest of Bermuda by this weekend.


TROPICAL STORM PHILIPPE... For much of Wednesday... Philippe continued moving primarily westward and failed to bend northward in track toward the current central Atlantic surface ridge weakness while now becoming entangled in a fujiwhara interaction with area of interest (AOI) #39 to the southeast which has moved closer to Philippe. In the upper-levels... the current warm core Caribbean upper ridge cell is in the process of amplifying northward toward the western Atlantic due to warm southerly flow ahead of ex-Ophelia... and later in the forecast period the western Atlantic upper ridge cell will become supported by warm southerly flow ahead of AOI #42. The southwest part of the nearby central Atlantic upper vorticity has begun to retrograde westward and away around the materializing western Atlantic upper ridge cell... which has allowed the central tropical Atlantic upper ridge cell to expand westward and reduce shear over Philippe. In turn this allowed Philippe to slightly strengthen to 50 mph maximum sustained winds... however the thunderstorms remain lopsided to the east side of the center as Philippe remains vulnerable to shear while at the northwest corner of the central Atlantic upper ridge cell. Noting between 1800Z and 0000Z Philippe abruptly jumped northward perhaps as the tropical storm has made an attempt at becoming a stronger/taller system which would expose the storm to southwesterly upper winds at the northwest corner of the upper ridge cell that would in fact try to yank Philippe northward.


Because Philippe has remained further south... it is now going to be further away from the steering surface ridge now approaching from eastern Canada and hence will move more slowly. This will now solidify the opportunity for AOI #39 to stay close to Philippe and hence deflect its track in a fujiwhara interaction. As such my updated forecast track below shows the northward angle in Philippe's slow westward track ending soon... followed by the formation of a southward slant to the slow westward track between 24 and 48 hours. From 48 to 72 hours I assume for now Philippe will stall just east of the northern Lesser Antilles while equally tugged by AOI #39 and the developing northwest Atlantic surface ridge weakness to be associated with AOI #42. And from 72 to 96 hours... as AOI #39 passes to the north of Philippe... I assume an eastward drift to Philippe's circulation from the ongoing fujiwhara interaction with AOI #39. For intensity... if Philippe follows the above-described forecast track the shear will be about the same through 24 hours and thus I show Philippe maintaining its current strength as it has been doing. Even though the southwest part of the central Atlantic upper vorticity is retrograding westward and away across the Caribbean as described in the prior paragraph... the remaining northeast part of the central Atlantic upper vorticity will be shoved southward toward Philippe by the aforementioned expanding western Atlantic upper ridge cell and also by the back side of the current northwest Atlantic upper trough. This will expose Philippe to more hostile northerly shear... followed by a lack of divergence directly below the arriving upper vorticity axis... or possibly even upper convergence to occur between the north side of the east-west upper vorticity axis and southeast side of the expanding western Atlantic upper ridge cell. Therefore weakening to a remnant low is shown in my updated forecast from 24 to 96 hours.


With each forecast update Philippe's forecast track has been moving closer to the northeastern Caribbean islands... and as of late the NHC official forecast and multiple global model runs suggest Philippe's center of circulation could move directly across the islands while my latest forecast has Philippe hanging out just east of the northern Lesser Antilles. Due to the unfavorable upper wind forecast noted above Philippe is most likely to be a weak circulation while interacting with the northeastern Caribbean islands... therefore the probability of gusty winds... heavy rain... and/or coastal surf remains low at this time. However interests in the northeastern Caribbean islands should remain aware of Philippe in case the upper wind forecasts change in future updates.

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

0 Hr Position (0000Z Sep 28)... 50 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 18.2N-54.5W

IOH 24 Hr Forecast (0000Z Sep 29)... 50 mph maximum sustained wind tropical storm centered east of the northern Lesser Antilles at 18.5N-57.5W

IOH 48 Hr Forecast (0000Z Sep 30)... 45 mph maximum sustained wind tropical storm centered east of the northern Lesser Antilles at 18N-59W

IOH 72 Hr Forecast (0000Z Oct 1)... 30 mph maximum sustained wind tropical depression centered east of the northern Lesser Antilles at 18N-59.5W

IOH 96 Hr Forecast (0000Z Oct 2)... Remnant low centered east of the northern Lesser Antilles at 18N-58W

******National Hurricane Center (hurricanes.gov) official forecast as of 11 PM EDT***************************

Loss of tropical cyclone status (0000Z Oct 2)... 35 mph maximum sustained wind tropical low centered over the northern Lesser Antilles at 18.5N-62.1W


AREA OF INTEREST #39... The tropical wave of low pressure that has been chasing Philippe is now in the central tropical Atlantic while displaying a sprawling spin centered near 14N-46W with squalls of curved thunderstorm bands. The track forecast shown below shows a continued northwestward track of this system into the open central Atlantic while hurtled in a fujiwhara interaction with Philippe... followed by attraction toward the surface ridge weakness associated with AOI #42. This system is behind my previous intensity forecast while failing to become a tropical cyclone so far. This is due to the fact this system has moved closer to Philippe than I previously thought... with Philippe's outflow suppressing the northwestern outflow of this system. My updated intensity forecast is thus notably lowered from my previous... and also the global models are showing a weaker system. I now assume over the next 72 hours this system will not strengthen past tropical depression status while dealing with northerly shear from Philippe's outflow and also the central Atlantic upper vorticity that will be hurtled toward Philippe and this system... and it also would not surprise me if this system also failed to become a tropical cyclone through 72 hours. By 96 hours... as this system moves into a lower shear environment beneath the western Atlantic upper ridge cell described in the above Philippe forecast discussion... I show strengthening into a tropical storm. By 120 hours I show no additional strengthening as this system begins to encounter westerly shear on the northern side of the western Atlantic upper ridge cell and out ahead of the upper vorticity associated with AOI #42. The southeastern divergence zone of the upper vorticity may aid this system by that time which is why I show no weakening at 120 hours despite the encounter with shear.

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

0 Hr Position (0000Z Sep 28)... Tropical low centered in the central tropical Atlantic at 14N-46W

IOH 24 Hr Forecast (0000Z Sep 29)... 35 mph maximum sustained wind tropical depression centered in the central tropical Atlantic at 17.5N-48W

IOH 48 Hr Forecast (0000Z Sep 30)... 35 mph maximum sustained wind tropical depression centered in the central Atlantic at 20N-52W

IOH 72 Hr Forecast (0000Z Oct 1)... 35 mph maximum sutained wind tropical depression centered in the central Atlantic at 22.5N-55W

IOH 96 Hr Forecast (0000Z Oct 2)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 25N-58W

IOH 120 Hr Forecast (0000Z Oct 3)... 45 mph maximum sustained wind tropical storm centered in the central Atlantic at 29N-59W

******National Hurricane Center (hurricanes.gov) official outlook as of 2 AM EDT***************************

Formation chance through 48 hours... 90%

Formation chance through 7 days... 90%


AREA OF INTEREST #41... The tropical wave of low pressure that was over the western Caribbean Sea has moved into Belize per the 0000Z NHC TAFB surface analysis. The remaining cloud deck with scattered showers and thunderstorms in the western Caribbean is likely a mid-level rotation that has been sheared northeastward from the tropical wave as upper southwesterlies over the tropical wave are increasing with the approach of the upper vorticity wave now over northeastern Texas. With the Belize landfall of the surface wave axis and increasing shear... tropical cyclone formation is no longer possible and this is my final statement on this area of interest on this blog.

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

IOH 24 Hr Outlook (0000Z Sep 29)... 0% chance of tropical cyclone formation (Guatemala/Mexico border near 17.5N-90.5W)

******National Hurricane Center (hurricanes.gov) official outlook as of 2 AM EDT***************************

Not in the official outlook


AREA OF INTEREST #42... The upper vortex now over the Great Lakes region of North America has recently merged with upper vorticity that has swung into northeast Texas from the southwestern US to make a wave of merged upper vorticity. The wave of upper vorticity will be moving offshore into the northwestern Atlantic by days 3 and 4 where it will trigger a surface frontal low with its eastern divergence zone. Even though the current eastern Canada surface ridge will tend to move offshore while following the convergence zone of the current northwestern Atlantic upper trough... a portion of the surface ridge will be maintained over eastern Canada by the western convergence zone of the wave of upper vorticity. In turn northward warm air transport on the west side of the persisting eastern Canada surface ridge will keep warm core upper ridging amplified over Canada such that the wave of upper vorticity has potential to consolidate into an offshore cut-off upper vortex by day 4. In this scenario the northwestern Atlantic surface frontal low would whirl beneath the cut-off upper vortex while still over warm enough waters to potentially acquire core thunderstorms and subtropical characteristics. Assigning a low 20% odds of subtropical cyclone formation for day 4 in this update as models are not consistent on whether or not the wave of upper vorticity will consolidate into a cut-off upper vortex... if this does not occur wind shear could end up being too high for subtropical development. By day 5 I return to 0% development odds as whatever subtropical circulation does develop would be caught under the west side of the eastward-shifting cut-off upper vorticity where suppressive upper convergence would be located. The weakening subtropical circulation would also be tracking southwest in the deep-layer northeasterly flow west of the upper vortex and on the south side of the eastern Canada surface ridge.


Regardless of whether or not the above-mentioned forecast northwest Atlantic frontal low acquires subtropical characteristics or not... this system could produce coastal surf for parts of the United States east coast and/or Bermuda by the weekend. For parts of the United States east coast... this would be a prolongation of the long-lasting period of coastal surf that has already been occuring due to the fetch of onshore-pushing wind caused by the pressure gradient between the north side of ex-Ophelia and south side of the eastern Canada surface ridge.

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

IOH 24 Hr Outlook (0000Z Sep 29)... 0% chance of subtropical cyclone formation (Maryland/ Pennsylvania border near 39.8N-78W)

IOH 48 Hr Outlook (0000Z Sep 30)... 0% chance of subtropical cyclone formation (just offshore of southeastern New Jersey near 38.8N-74W)

IOH 72 Hr Outlook (0000Z Oct 1)... 0% chance of subtropical cyclone formation (offshore of the eastern United States near 37N-70W)

IOH 96 Hr Outlook (0000Z Oct 2)... 20% chance of subtropical cyclone formation (offshore of the eastern United States near 37N-69.5W)

IOH 120 Hr Outlook (0000Z Oct 3)... 0% chance of subtropical cyclone formation (offshore of the eastern United States near 35.5N-71.5W)

******National Hurricane Center (hurricanes.gov) official outlook as of 2 AM EDT***************************

Not in the official outlook


...COMPUTER MODEL SUMMARY...

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


1200Z (Sep 27) CMC Model Run...

**For Tropical Storm Philippe... moves west-northwest to 19.8N-57.5W through 42 hours while remaining a weak tropical cyclone... subsequently interaction with area of interest #39 causes Philippe to drift west-southwest into the north coast of the Dominican Republic through 120 hours while weakening to a remnant tropical wave

**For Area of Interest #39... tropical cyclone formation suggested near 16N-45.5W at 18 hours... reaches 20.5N-59W at 120 hours as a tropical storm

**For Area of Interest #41... no development shown

**For Area of Interest #42... broad frontal low that contains ex-Ophelia develops near 37N-72.8W by 60 hours... broad frontal low continues east while having multiple centers and reaches the vicnity of 36N-59W by 120 hours.


1200Z (Sep 27) ECMWF Model Run...

**For Tropical Storm Philippe... moves west-northwest to 19N-58.5W through 42 hours while weakening to a remnant low... subsequently the remant low drifts west-southwest while interacting with area of interest #39 with the remnant low dissipating over the Virgin Islands by 90 hours

**For Area of Interest #39... tropical cyclone formation suggested near 17.5N-45.5W at 30 hours... tropical cyclone reaches 19N-57W by 120 hours while not strengthening past tropical storm status.

**For Area of Interest #41... no development shown

**For Area of Interest #42... broad frontal low that contains ex-Ophelia develops near 37.5N-70W by 72 hours... broad frontal low continues east while having multiple centers and reaches the vicnity of 36N-60W by 120 hours.


1800Z (Sep 27) GFS Model Run...

**For Tropical Storm Philippe... while gradually strengthening drifts northwest to 20N-55W through 33 hours... subsequently stalls then drifts southeast through 102 hours while in a fujiwhara interaction with area of interest #39 and intensifies into a hurricane near 17.5N-53.8W... hurricane then moves north toward surface ridge weakness associated with areas of interest #39 and #42 and reaches 20.5N-53.8W by 120 hours.

**For Area of Interest #39... tropical cyclone formation suggested near 18N-45.5W at 24 hours... subsequently moves northwest and then west-northwest while swinging around Philippe and reaches 27.5N-59W at 120 hours while weakening to a remnant low

**For Area of Interest #41... no development shown

**For Area of Interest #42... east-west elongated frontal low develops near 36.5N-69.5W at 60 hours... subsequently strengthens into a more circular frontal cyclone with possible subtropical characteristics near 36N-68W by 87 hours... frontal cyclone subsequently moves southwest to 33.5N-71W through 120 hours.


1800Z (Sep 27) NAVGEM Model Run...

**For Tropical Storm Philippe... drifts northwest to 18.8N-56W through 36 hours... subsequently becomes quasi-stationary through 90 hours due to fujiwhara interaction with area of interest #39 while strengthening into a hurricane... hurricane then moves north to 21.5N-56W through 120 hours while moving toward surface ridge weakness associated with area of interest #42.

**For Area of Interest #39... tropical cyclone formation suggested near 17.5N-56W at 12 hours... subsequently curves north and then north-northeast ahead of Philippe and then area of interest #42 and reaches 33.5N-45.5W at 120 hours while not strengthening past compact tropical storm status

**For Area of Interest #41... no development shown

**For Area of Interest #42... broad frontal low that contains ex-Ophelia develops near 35N-72.5W at 42 hours... subsequently strengthens into a frontal cyclone with possible subtropical characteristics near 38.8N-68.5W by 78 hours... frontal cyclone then swings southeast to 35.5N-60.5W through 120 hours.

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