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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 #84

Updated: Sep 24, 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...SUNDAY SEPTEMBER 24 2023 10:57 PM EDT...

The birdseye view chart below has been updated to now include the surface and upper-level analysis as of 1800Z today.


...SUNDAY SEPTEMBER 24 2023 4:08 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 later this evening. This update is released now without those parts of the chart to ensure a timely release of this update.


See remnants of Ophelia section below for an update on the frontal low pressure over the mid-Atlantic region of the United States that was formerly Tropical Storm Ophelia. Tropical Depression Seventeen in the open central tropical Atlantic became Tropical Storm Philippe last evening... see Philippe section below for more information on the new tropical storm. See Area of Interest #39 section below for more information on the latest eastern Atlantic tropical wave of low pressure being monitored for signs of development over the course of the next few days... and see area of interest #40 section below for information on a surface trough of low pressure in the southern Gulf of Mexico the NHC is now monitoring for signs of development.


Elsewhere... concentrated showers and thunderstorms have developed in the open central Atlantic near 25N-60W and underneath a string of upper vorticity (the same upper vorticity currently shearing Philippe). This cool core upper vorticity string has been undergoing some decay due to prolonged isolation from high-latitude cold air and appears to be splitting in half. The above-mentioned activity is probably being generated by split flow upper divergence between two halves of the upper vorticity... however the CIMSS 850 mb vorticity product does not show much of a spin/low-level trough of low pressure in progress at this time (https://tropic.ssec.wisc.edu/real-time/windmain.php?basin=atlantic&sat=wg8&prod=vor&zoom=&time=). Any surface trough that does develop here will be moving northwestward toward the vicnity of Bermuda around the west side of the current Atlantic surface ridge. Upper winds over the next 24 hours are conducive for development underneath the low shear/outflow of a current northwestern Atlantic upper ridge cell. However by 48 hours upper winds will become hostile as westerly shear in the region increases with the approach of the north fracture of the current eastern North America upper trough. Without a surface or low-level trough in progress yet... it will be hard for tropical cyclone formation to occur in the short term before upper winds become hostile by 48 hours... and tropical cyclone development here is not anticipated (also global models show no development in this region).


REMNANTS OF OPHELIA... The surface circulation of Ophelia is continuing north-northeastward in the flow on the east side of a lengthy eastern North America upper trough which is the result of the merger between upper troughs over eastern Canada and the southeastern United States. Ophelia has transitioned into a remnant non-tropical frontal low pressure supported by the eastern divergence zone of the upper trough and whose center is crossing the Washington DC region as of this writing. The northern part of the upper trough will continue offshore and will drag ex-Ophelia eastward across southeastern Maryland... Delaware... and southern New Jersey with it. However the strong surface ridge over eastern Canada will tend to resist ex-Ophelia's eastward acceleration such that ex-Ophelia will end up underneath the suppressive western convergence zone of the northern fracture of the upper trough... thus ex-Ophelia is expected to continue weakening over time. Based on recent National Weather Service station reports (weather.gov) in northern New Jersey as well as southeastern New York... Long Island New York... and coastal Connecticut... winds are still breezy in the region due to the pressure gradient between ex-Ophelia and the surface ridge. These breezy winds are also driving a coastal surf in this region as well... although any breezy winds and coastal surf that continue here or elsewhere along the United States east coast over the next few days will be a reflection of the strength of the surface ridge as ex-Ophelia continues to weaken and fade away. Based on the latest radar presentation additional periods of heavy rain with isolated flash flooding potential will continue across eastern Pennsylvania... New Jersey... southeastern New York... Connecticut... Rhode Islands... Massachusetts... Rhode Island... southern Vermont... and southern New Hampshire. This is my final statement on Ophelia on this blog as it is no longer a tropical cyclone... refer to the home page bulletins of this site for more information on impacts from Ophelia's remnants.


The following are the peak wind gusts (in mph) recorded at each of the following National Weather Service stations (weather.gov) over the last several hours:

**Accomac (Delmarva Peninsula VA)... sustained 17... gust 25 (1:15 AM EDT Sept 24)

**Elkton (northeast corner of MD)... sustained 28... gust 40 (8:51 PM EDT Sept 23)

**Washington DC... sustained 28... gust 38 (3:52 PM EDT Sept 23)

**Dover DE... sustained 26... gust 39 (4:55 PM EDT Sept 23)

**Atlantic City (southeastern NJ)... sustained 23... gust 41 (6:54 PM EDT Sept 23)

**Trenton (west-central NJ)... sustained 24... gust 36 (7:53 AM EDT Sept 24)

**La Guardia Airport (southeastern NY)... sustained 29... gust 40 (8:51 PM EDT Sept 23)


TROPICAL STORM PHILIPPE... Tropical Depression Seventeen has strengthened into Tropical Storm Philippe as of Saturday evening. The thunderstorm canopy of the tropical storm remains lopsided toward the east side of the surface center... an indication that central Atlantic upper vorticity continues to shear the tropical storm. The current position of Philippe is east of the previous forecast... and my updated one is adjusted accordingly. The more east position of Philippe could be an indication that Philippe's surface center has been trying to consolidate toward surface pressure falls caused by the warm core upper ridging and outflow generated by the thunderstorm canopy's latent heat release. The track forecast calls for an increase in the north angle of Philippe's westward track going forward under the influence of the current central Atlantic upper vorticity... followed by the development of a surface ridge weakness in the open central Atlantic triggered by the eastern divergence zone of what will be the northern fracture of the current eastern North America upper trough as that fracture moves into the northwest Atlantic. For intensity... I call for possible additional strengthening in the next 24 hours before the shear worsens when Philippe moves closer to the shearing central Atlantic upper vorticity. Between 24 and 48 hours I call for weakening from the worsening shear. By 72+ hours the westerly shear across Philippe may let up as the central Atlantic upper vorticity becomes tilted southwest-to-northeast under the influence of a strengthening Caribbean upper ridge cell... changing the upper winds over Philippe from westerly to southwesterly. Thus I show some recovery in strength for that timeframe... but not much as the southwesterly shear may still be strong.


Noting that due to the east shift in Philippe's forecast track that the potential for coastal surf to reach the shores of the northern Lesser Antilles by the middle of this upcoming week has ended.

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

0 Hr Position (1200Z Sep 24)... 50 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 16.2N-41.7W

IOH 24 Hr Forecast (1200Z Sep 25)... 60 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 17.2N-45.5W

IOH 48 Hr Forecast (1200Z Sep 26)... 45 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 18.2N-50W

IOH 72 Hr Forecast (1200Z Sep 27)... 50 mph maximum sustained wind tropical storm centered in the central tropical Atlantic at 20.5N-52.5W

IOH 96 Hr Forecast (1200Z Sep 28)... 50 mph maximum sustained wind tropical storm centered in the central Atlantic at 22.5N-53W

IOH 120 Hr Forecast (1200Z Sep 29)... 50 mph maximum sustained wind tropical storm centered in the central Atlantic at 25N-54W

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

5-Day Position (1200Z Sep 28)... 65 mph maximum sustained wind tropical storm centered in the central Atlantic at 24N-55.5W


AREA OF INTEREST #39... The latest tropical wave of low pressure in the eastern tropical Atlantic has seen its center of rotation consolidate further south and east near 9N-26W as of 1200Z today. The shower and thunderstorm activity is scattered around this center of rotation. Forecast track in the outlook below curves increasingly northward with time while gravitated toward the surface ridge weakness associated with what is now Tropical Storm Philippe. The southward relocation of the center of rotation could be due to the better upper outflow environment away from the suppressing eastern Atlantic upper vorticity and toward the eastern tropical Atlantic upper ridge axis. With the updated initial position and forecast track now further away from the suppressing upper vorticity... the potential for development of this tropical wave has increased and indeed the GFS and ECMWF are picking up on this. However I have not yet selected peak odds of development above 50% as not all global models (for example the CMC and NAVGEM) develop this system... and by day 5 this system may begin to struggle with northerly shear imparted by the outflow of Tropical Storm Philippe. Beyond day 5 this system is at risk of being sheared apart and absorbed by relatively stronger Philippe if this system has not become a tropical cyclone by then.

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

IOH 24 Hr Outlook (1200Z Sep 25)... 20% chance of tropical cyclone formation (eastern tropical Atlantic near 10N-31W)

IOH 48 Hr Outlook (1200Z Sep 26)... 30% chance of tropical cyclone formation (eastern tropical Atlantic near 11N-36W)

IOH 72 Hr Outlook (1200Z Sep 27)... 40% chance of tropical cyclone formation (central tropical Atlantic near 12.5N-40W)

IOH 96 Hr Outlook (1200Z Sep 28)... 50% chance of tropical cyclone formation (central tropical Atlantic near 15N-43W)

IOH 120 Hr Outlook (1200Z Sep 29)... 50% chance of tropical cyclone formation (central tropical Atlantic near 17.5N-46W)

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

Formation chance through 48 hours... 20%

Formation chance through 7 days... 60%


AREA OF INTEREST #40... A surface trough of low pressure with somewhat concentrated and organized thunderstorms has developed in the southern Gulf of Mexico near 22.5N-86W. The NHC has added this feature into their tropical weather outlook as of 2 PM EDT... this is the fortieth tropical Atlantic area of interest tracked on this site this year.


This feature has developed due to upper divergence on the east side of the southern base of the current eastern North America upper trough. This part of the upper trough is forecast to evolve into a southward drifting cut-off upper vortex pushed by the upper ridge cell that has been persisting over Mexico. Therefore the surface trough is expected to drift west while pulled by the north side of the upper vortex and south side of the current eastern Canada surface ridge... however with the surface ridge expected to remain far away this system will have rather slow westward progression. The forecast track by 24 hours already places the surface trough underneath the northwest side of the upper vortex where upper convergence between the northwest quadrant of the vortex and east side of the Mexico upper ridge cell will likely squash development potential. If the westward-drifting surface trough does persist beyond 48 hours... the next obstacle it will encounter will be westerly shear as upper vorticity currently offshore of Baja California and California zooms eastward into the northwestern Gulf of Mexico while moving around the north side of the Mexico upper ridge... with this upper vorticity unfavorably shearing the surface trough. With this unfavorable upper wind outlook for the surface trough... global models shy away from developing this feature and I am assigning a 0% odds of tropical cyclone formation at this time.

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

IOH 24 Hr Outlook (1200Z Sep 25)... 0% chance of tropical cyclone formation (southern Gulf of Mexico near 22.5N-88W)

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

Formation chance through 48 hours... 10%

Formation chance through 7 days... 10%


...COMPUTER MODEL SUMMARY...

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


0000Z (Sep 24) CMC Model Run...

**For Tropical Storm Philippe... reaches 25.5N-56W at 120 hours as a strong tropical storm approaching hurricane strength

**For Area of Interest #39... moves toward Philippe and reaches 16.5N-47.5W at 120 hours as a tropical low

**For Area of Interest #40... no development shown


0000Z (Sep 24) ECMWF Model Run...

**For Tropical Storm Philippe... reaches 23N-58.5W at 120 hours while still a weak tropical storm

**For Area of Interest #39... tropical cyclone formation suggested near 16.5N-46W at 126 hours

**For Area of Interest #40... no development shown


0600Z (Sep 24) GFS Model Run...

**For Tropical Storm Philippe... weakens to an elongated remnant low near 16.2N-51.2W at 63 hours... elongated remnant low then lifts north and re-develops into a tropical cyclone near 21.5N-52.5W at 87 hours... turns northwest and reaches 23.8N-55W by 120 hours as a tropical storm

**For Area of Interest #39... tropical cyclone formation suggested near 15N-41.2W at 93 hours... tropical cyclone reaches 17N-45W at 120 hours.

**For Area of Interest #40... no development shown

**Upper vortex currently over the north-central US moves into North Carolina and Virginia through 168 hours where its eastern divergence zone produces a strong and elongated subtropical surface low just offshore of the North Carolina Outer Banks.


0600Z (Sep 24) NAVGEM Model Run...

**For Tropical Storm Philippe... curves north and reaches 28.8N-50.5W through 120 hours as an intense hurricane

**For Area of Interest #39... no development shown

**For Area of Interest #40... surface low located in the southern Gulf of Mexico to the west-northwest of western Cuba moves west to 24N-94W through 60 hours... from this location becomes stationary while gradually dissipating through 162 hours.

**Northern part of current eastern North America upper trough moves offshore into the northwestern Atlantic through 168 hours... produces a potential subtropical cyclone west of Philippe and near 38.5N-55.5W by 168 hours

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