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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 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.**********

...TUESDAY JULY 13 2021 10:55 PM EDT...

Satellite image as of 2150Z. Areas of interest circled in yellow are not mentioned in the NHC tropical weather outlook. Areas circled in a green dashed line are in the NHC 5-day tropical weather outlook. Areas circled in a solid green line are in the NHC 2-day tropical weather outlook:

NHC TAFB Surface Analysis 1800Z:

GFS Model Upper-Level Winds 1800Z:

See area of interest #1 section below for an update on the potential for tropical development in northwest Atlantic waters to the north of Bermuda. Elsewhere…a surface tropical wave of low pressure in the western Caribbean has seen an increase in thunderstorms due to supportive outflow beneath a local-scale upper ridge in the region which has been able to develop in the wake of the upper vortex that recently lifted into the southeast US from the western Atlantic. However the tropical wave is already interacting with the landmasses of Central America and southeast Mexico…and the local-scale upper ridge will soon become suppressed as the central Atlantic upper vorticity retrogrades southwest into the Caribbean under the influence of the sprawling upper ridge in the northwest Atlantic. Tropical development in the western Caribbean is thus not expected.

AREA OF INTEREST #1A rather lengthy continuous surface frontal zone separating cool air to the north and warm air to the south stretches from the current frontal low over the Great Lakes region of North America to the remnant low of Elsa located just offshore of southeast Greenland. A cloud swirl surface low pressure has developed along the front in the open northwest Atlantic… at a location near 38N-58W…while supported by split flow upper divergence between the west side of the upper trough that has recently entered the northwest Atlantic from eastern Canada and east side of the sprawling upper ridge also in the northwest Atlantic. A surface ridge to the north is forecast to push the cloud swirl surface low westward toward warmer water and toward the center of the sprawling upper ridge where wind shear is low and upper outflow is higher…and the NHC as a result has joined in on declaring the surface low an area of interest for tropical development in their tropical weather outlook.

I have shifted the forecast positions in my updated outlook below to the east where the surface low pressure swirl has formed. I support slightly raising odds of tropical cyclone formation to 15% due to the presence of a cloud swirl structure and slightly more favorable conditions that lie ahead (as mentioned in the prior paragraph) as the surface low drifts west over the next 48 hours. I do not support higher odds of development at this time as the models do not forecast much development of the surface low and there is currently a lack of showers and thunderstorms. By 72 hours I end the outlook (bring development odds to 0%) as the forecast track is expected to bend north while the surface low rounds the west side of the steering surface ridge…which will take the surface low to cooler water.

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

IOH 24 Hr Outlook (0000Z Jul 15)…15% chance of tropical cyclone formation (northwest Atlantic near 37.5N-60W)

IOH 48 Hr Outlook (0000Z Jul 16)…15% chance of tropical cyclone formation (northwest Atlantic near 38N-61W)

IOH 72 Hr Outlook (0000Z Jul 17)…0% chance of tropical cyclone formation (northwest Atlantic near 42.5N-57.5W)


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

1200Z CMC Model Run...

**For area of interest #1...surface low drifts southwest to 37N-59.8W by 30 hours…weakens to a surface trough at 60W longitude at 36 hours.

1200Z ECMWF Model not available at above-mentioned source

1800Z GFS Model Run...

**For area of interest #1...some tropical development suggested over next 6 hours…surface low then weakens while drifting west to 37N-60W by 30 hours…weakens to a surface trough near 37.5N-62W by 54 hours.

1800Z NAVGEM Model Run...

**For area of interest defined surface low pressure shown.

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