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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 

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*******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 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 dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********

...SUNDAY AUGUST 27 2023 4:25 PM EDT...

This special update is to issue a track forecast and probabilities of tropical cyclone formation for the current central Atlantic tropical wave currently heading for the Lesser Antilles and Caribbean as this was not included in previous full update #64... see area of interest #28 section below for more information. Refer to full update #64 at the following link for more information on Hurricane Franklin in the western Atlantic... Tropical Storm Idalia in the northwest corner of the Caribbean... and other areas of interest being monitored for tropical development in the Atlantic basin...

AREA OF INTEREST #28... Visible satellite image of Tropical Storm Idalia... Hurricane Franklin... and a central Atlantic tropical wave of low pressure as of 1820Z. This area of interest is focused on the tropical wave:

A central Atlantic tropical wave of low pressure with a distinct area of showers and thunderstorms was positioned near 9N-47.5W as of 1800Z... at times the activity has shown signs of organization. In the upper-levels an upper anticyclone covering the western Atlantic and Caribbean is expected to solidify once the upper vortex over the southeastern Bahamas dissipates from prologned isolation from high-latitude cold air... allowing the merger between Franklin's outflow... the current Caribbean tropical upper ridge axis... and the upper ridge cell currently offshore of the southeastern US. This anticyclone will push a nearby upper trough southward into this tropical wave... and then through 72 hours chase the wave westward as a suppressing inverted upper trough while continuing to be pushed by the anticyclone. It is not until 96+ hours that the wave escapes the inverted upper trough as it continues into and across the central Caribbean Sea... and potentially is exposed to a better upper outflow environment on the south side of the upper anticyclone. I assign a low 10% odds of tropical cyclone formation by day 5 as this system will have only had a short time in the better upper air pattern by then... and it is also possible this system may struggle with light easterly shear since it will be south of the upper anticyclone center instead of beneath it.

Regarding the forecast track... the wave is expected to continue west across the southern Lesser Antilles by late Tuesday. Although the southeastern convergence zone of the western Atlantic upper anticyclone will produce a weak surface ridge to the north of the Caribbean... and to the south of Idalia and Franklin as those two storms lift northward and away... this wave will tend to be toward the west extent of the surface ridge. Therefore the forecast track below indicates some increase in the northward angle of the westward track as this system moves across the Caribbean. This wave may not produce much rainfall across the southern Lesser Antilles as it may be suppressed by the aforementioned inverted upper trough at the time it crosses the islands.

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

IOH 24 Hr Outlook (1800Z Aug 28)... 0% chance of tropical cyclone formation (central tropical Atlantic near 10N-52.5W)

IOH 48 Hr Outlook (1800Z Aug 29)... 0% chance of tropical cyclone formation (east of the southern Lesser Antilles near 10.5N-57.5W)

IOH 72 Hr Outlook (1800Z Aug 30)... 0% chance of tropical cyclone formation (southeastern Caribbean Sea near 11.5N-62.5W)

IOH 96 Hr Outlook (1800Z Aug 31)... 0% chance of tropical cyclone formation (southeastern Caribbean Sea near 13N-67.5W)

IOH 120 Hr Outlook (1800Z Sep 1)... 10% chance of tropical cyclone formation (central Caribbean Sea near 15N-73W)

******National Hurricane Center ( official outlook as of 2 PM EDT*****************************

Not in the official outlook

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