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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 2024 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #89A (Special Update)

*******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… THURSDAY SEPTEMBER 26 2024 6:00 PM EDT...

Helene has strengthened further to 125 mph maximum sustained winds as of 5 PM EDT. Multiple tornado warnings are occuring across the Florida peninsula… eastern Florida panhandle… Georgia… and the Carolinas as directional wind shear favoring severe thunderstorms and tornadoes is present (combo of southeasterly surface flow in advance of Helene and upper southwesterlies ahead of the eastern North America upper trough). Interests here should listen to local news media to be prepared to shelter from tornadoes through tonight.


...THURSDAY SEPTEMBER 26 2024 3:25 PM EDT...

Releasing my updated track and intensity forecast for Hurricane Helene now due to the large swath of land areas that this system is expected to impact. My full update which includes information on Tropical Storm Isaac in the open north Atlantic... and on current disturbances across rest of the Atlantic tropics... will be released later this evening.


HURRICANE HELENE (RECENTLY UPGRADED TO MAJOR HURRICANE HELENE)... Visible satellite image of recently-upgraded Major Hurricane Helene as of 1911Z:

I completed the following forecast on Helene based on satellite imagery and model data available from 1200Z to 1700Z earlier today. Since then... Helene has rapidly intensified into a major category 3 hurricane with 120 mph maximum sustained winds... and it is likely that the intensity forecast shown below is now too low which means the potential for catastrophic wind damage and coastal storm surge for the small area that will be exposed to Helene's eye at tonight's landfall (in the far eastern Florida panhandle) is increasing. Will have an updated discussion on Helene during my next full update planned for later this evening.


As expected the upper vorticity that was in the eastern Bay of Campeche has merged with the incoming eastern North America upper trough... with the merger resulting in a lengthy upper trough driving Helene north-northeast across the eastern Gulf of Mexico. Previously it appeared dry sinking air induced by the western convergence zone of the prior Bay of Campeche upper-level disturbance was wrapping into Helene... resulting in frequent episodes of broken thunderstorm bands on colorized infrared satellite imagery over much of the last 24 hours and only a gradual strengthening rate to category 2 status. Because the axis of the lengthy upper trough is currently off to the west... the dry sinking air zone is now further west and away from Helene (over the south-central US) and Helene has gotten its act together in recent hours by having a more solid thunderstorm core. And at around 1700Z Helene is finally establishing a better-defined eye featuring a hot tower burst on the eastern eyewall. The general symmetry of the core around the eye suggests the latent heat release of the core thunderstorms have built a local shear-reducing warm core upper anticyclone over the hurricane... and the northern outflow of the local upper anticyclone is likely being enhanced by the southwesterly flow ahead of the lengthy incoming upper trough. Given that Helene has strengthened a little faster than my previous intensity projection... the improved satellite appearance... and that we are trending toward an upper air setup that favors less shear and outflow enhancement as feared as a possibility yesterday... I have bumped up my intensity forecast and currently call for Helene to become a major category 3 hurricane as the center approaches landfall with the far eastern Florida panhandle by late tonight. I have not selected a higher intensity forecast than 120 mph maximum sustained winds as the approaching upper trough axis and associated stronger upper flow approaches Helene around landfall time... which may help to stress Helene and its local upper anticyclone. My track forecast is the same as previous... however shows landfall occurring just a touch later in line with the latest model consensus which is perhaps another indication that Helene has a local upper anticyclone over it that is not only deflecting wind shear... but also slightly numbing the steering effect of the upper southwesterly flow. After landfall... the south part of the steering upper trough is forecast to become a cut-off upper vortex to the east of an amplified upper ridge... with Helene arcing north then eventually west around the northeast half of the upper vortex... a path that takes the inland remnant system across the eastern US. During this time Helene transitions into a remnant frontal cyclone supported by the eastern divergence zone of the steering upper vortex. Note that Helene is a large system where its storm force wind field extends outside of its thunderstorm core... as it was born within a broad low pressure field... and will continue to remain large due to the size of the eastern divergence zone of the steering upper trough/vortex. In fact as of this writing tropical storm force gusts are already occurring across the Florida Keys and southwestern Florida peninsula which are located well outside the thunderstorm core. The large wind field will drive a life-threatening widespread coastal storm surge toward the landfall region regardless of the exact category number assigned to Helene's peak intensity. Final note regarding intensity... the post-landfall decay rate of Helene could be slower than normal due to the aforementioned field of upper divergence.


Regarding impact to land areas:

(1) For western Cuba… outer bands of heavy rainfall and gusty winds will occur for a few more hours until the large outer circulation of Helene pulls north and away.

(2) Coastal surf has arrived across the Florida Keys and southwestern half of the Florida peninsula coast by now... and will continue to spread across the remainder of the peninsula west coast... panhandle coast... and Alabama coast through tonight. The coastal surf becomes severe and life-threatening by tonight for the eastern Florida panhandle and northwestern Florida peninsula... listen to the advice of local government officials and news media... particularly evacuation orders.

(3) Given Helene's current wind field size... tropical storm gusts with isolated damage potential are expected across all of the Keys and Florida peninsula... as well as the eastern and central part of the Florida panhandle. More severe wind damage from stronger tropical storm to hurricane force winds are expected across the northwestern Florida peninsula... eastern panhandle... and southern Georgia by tonight. As a large remnant frontal cyclone... ex-Helene could bring a large swath of gusty winds with scattered damage potential across Georgia... Alabama... Mississippi... eastern Arkansas... southeastern Missouri... Tennessee... Kentucky... southern Illinois... southern Indiana... southern Ohio... the western Virginias (including most of West Virginia)... and the western Carolinas through Friday and Saturday.

(4) Expect heavy rainfall with flash flooding potential across all of Florida... Georgia... Alabama... Mississippi... eastern Arkansas... southeastern Missouri... Tennessee... Kentucky... southern Illinois... southern Indiana... southern Ohio... the Virginias... and the Carolinas through Friday and Saturday.

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

0 Hr Position (1200Z Sep 26)... 105 mph maximum sustained wind hurricane centered in the eastern Gulf of Mexico at 25.5N-85.5W

IOH 12 Hr Forecast (0000Z Sep 27)... 120 mph maximum sustained wind major hurricane centered just offshore of the far eastern Florida panhandle at 29.5N-83.8W

IOH 24 Hr Forecast (1200Z Sep 27)... Remnant frontal cyclone centered over the northwestern corner of South Carolina at 34.5N-82.8W

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

Peak Strength (0000Z Sep 27)... 120 mph maximum sustained wind major hurricane centered just offshore of the eastern Florida panhandle at 28.8N-84.3W

3-Day Position (1200Z Sep 29)... 25 mph maximum sustained wind dissipating remnant low centered over the western Kentucky/Tennessee border at 36.2N-87.2W

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