Since 2012 on the 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 via Disqus on Weather Underground at You can see my Disqus feed at this link for my latest comments. Feel free to reply to me with your disqus account or e-mail at 

  • NCHurricane2009


*******Note that forecasts 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.**********

...FRIDAY JULY 16 2021 9:10 AM EDT...

Satellite imagery of the northwestern Atlantic surface low pressure taken at 1210Z. To the left is the right is water vapor imagery which reveals the location of an approaching upper trough to the west (blue-dashed line) which is decaying into multiple smaller vortices (blue Ls). The center of the surface low pressure is marked with a red L...with blue arrows showing the divergent flow aloft currently aiding the surface low:

The surface low pressure area in the northwestern Atlantic has made a comeback overnight while the eastern of two smaller vortices has become the dominant while also firing thunderstorm activity over and southeast of the new center. Using zoomed-in satellite imagery of the surface low (available at new more eastern center is currently located at 40N-56.8W and is on a northeast heading while rounding the northwest side of the steering surface ridge in the region. This places the surface low in between warm waters spots at 41N-58W just to the west and 39N-56W just to the southeast according to the latest sea surface temperature analysis (available at Perhaps it is the warm water spot to the southeast that is helping the thunderstorm activity which is on the southeast side of the circulation. In addition...this system is being aided by divergent flow aloft on the east side of a small upper vortex approaching from the west as illustrated by the above water vapor satellite imagery. Therefore in this special update...I have re-initiated this system as an area of interest for tropical development...forecasting a 15% chance of tropical cyclone formation in the next 12 hours...followed by a 0% chance by 24 hours when the northeast track of this system will take it more firmly into cooler waters. I have kept the odds low due to currently northwesterly shear caused by the upper-level flow which is keeping the thunderstorms limited to the southeast half of the circulation...and because the National Hurricane Center (NHC) has not re-initiated this system as an area of interest in their outlook product as of this writing.

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

IOH 12 Hr Outlook (0000Z Jul 17)...15% chance of tropical cyclone formation (northwest Atlantic near 42N-54W)

IOH 24 Hr Outlook (1200Z Jul 17)...0% chance of tropical cyclone formation (northwest Atlantic near 43N-51W)

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