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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.**********

...THURSDAY JULY 13 2023 12:07 PM EDT...

Surface low pressure cyclone to meander in the open central Atlantic over the next several days and is likely to gain subtropical or tropical status in the short-term... see area of interest #13 section below for more information. Elsewhere... the tropical belt of the Atlantic remains calm as the Caribbean is covered by suppressing upper vorticity and the central and eastern tropical Atlantic has a swath of dry Saharan air being wafted across from Africa.

AREA OF INTEREST #13... The central Atlantic surface low pressure area as expected has transited eastward while steered by the south side of upper vortiicty in the region... and is expected to strengthen further into a cyclone over the next 24 hours while now having arrived into the supportive eastern divergence zone of the vorticity. This system is located southwest of the previous forecast track and is therefore likely to be near the 26 deg C sea surface temperature isotherm for a little longer. In addition organizing thunderstorm activity has developed in the east half of the circulation... and the GFS has joined the other models in consolidating the upper vorticity and associated supportive divergence zone such that a well-defined surface center develops with the surface cyclone. These notes suggest that there is a high chance of this system becoming a subtropical cyclone in the next 24 hours... meaning its strength is derived by both the traditional non-tropical process (divergence zone of cold core upper vorticity) and the tropical process (latent heat release of thunderstorms developing a layer of warm core upper ridging and outflow that also results in a drop in surface pressures). As a result I have notably increased my peak odds of subtropical cyclone formation to 80% for the short-term... with odds tapering down to 0% through 72 hours as this system moves northward away from the 26 deg C isotherm while steered by the east side of the upper vorticity. Also noting that the upper vorticity is also not particularly cold enough to generate instability and thunderstorms over water temps below 26 deg C.

Through 48 hours there is a westward slant in the norhtward forecast track as this system cyclonically arcs around the east side of the upper vorticity. Beyond that time the track is expected to then take an eastward slant as some of the upper vorticity from the current eastern North America upper vortex finally breaks through the northwest Atlantic upper ridge and moves toward this system and associated central Atlantic upper vorticity... with all the upper vorticity combining into an eastward-moving supporting upper trough in the environment of this system. In the long range (beyond 5 days)... models are increasingly suggesting that the warm core northwest Atlantic upper ridge then rebuilds in the warm sectors of additional surface frontal systems to be generated by the ongoing North American upper vortex... with the central Atlantic upper trough and surface cyclone taking a southward dive back toward warmer waters under the influence of the re-amplifying ridge. Therefore the central Atlantic system may have two shots at gaining tropical status... one in the short-term (next 48 hours)... and then again in the long term (beyond 5 days).

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

IOH 24 Hr Outlook (1200Z Jul 14)... 80% chance of subtropical cyclone formation (central Atlantic near 33N-46W)

IOH 48 Hr Outlook (1200Z Jul 15)... 50% chance of subtropical cyclone formation (central Atlantic near 37N-47W)

IOH 72 Hr Outlook (1200Z Jul 16)... 0% chance of subtropical cyclone formation (central Atlantic near 39N-45W)

******National Hurricane Center ( official outlook as of 8 AM EDT***************************

Formation chance through 48 hours...60%

Formation chance through 7 days (168 hours)...60%


Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (

0000Z (Jul 13) CMC Model Run...

**For area of interest #13...subtropical cyclone suggested near 33N-47.5W at 36 hours... curves north to 38.5N-47W through 102 hours where it maintains some strength as a potentially less tropical system over cooler waters... the persisting and gradually weakening surface low then curves southeast to 37N-45W through 120 hours

**Tropical wave currently over western Africa evolves into a tropical low in the central tropical Atlantic that reaches 13.5N-50.5W by 168 hours

0000Z (Jul 13) ECMWF Model Run...

**Not available at above-mentioned source

0600Z (Jul 13) GFS Model Run...

**For area of interest #13... subtropical cyclone suggested near 33N-46W at 21 hours... curves north to 39N-45W through 78 hours where it maintains strength as a potentially as a less tropical system over cooler waters... the persisting surface low then curves east-southeast to 36N-39.8W through 120 hours.

0600Z (Jul 13) NAVGEM Model Run...

**For area of interest #13... subtropical cyclone suggested near 32N-46W at 18 hours... curves north to 39N-45.5W through 84 hours where it maintains strength as a potentially as a less tropical system over cooler waters... the persisting surface low then curves east-southeast to 36N-40W through 120 hours.

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