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 

  • 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.**********

…THURSDAY OCTOBER 21 2021 12:30 AM EDT...

Satellite image as of 0220Z. 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 (Wednesday Oct 20):

GFS Model Upper-Level Winds 1800Z (Wednesday Oct 20):

Showers and thunderstorms in the western Caribbean Sea… southeastern Mexico… and Central America… supported by the outflow of an upper ridge in the region… have become less organized and more scattered. Computer models insist the upper ridge is forecast to aid in tropical cyclone formation in the eastern Pacific. Tropical cyclone formation in the Caribbean is therefore not expected.

Elsewhere… a large area of cold core upper vorticity is currently located over the northeastern Pacific to the south of Alaska while a deep-layer warm upper ridge is over western Canada. Over the next week… computer models forecast a piece of this upper vorticity to slide east across the United States and to the south of the deep-layer ridge. Meanwhile the deep-layer ridge will remain supported by the warm sector of various western Canadian frontal lows to be supported by the remainder of the northeastern Pacific upper vorticity to remain left behind. This amplified deep-layer ridge could cause the upper vorticity sliding across the US to retain an equally amplified signature as it moves into the western Atlantic. As shown by the GFS model in recent days… the amplified upper vorticity could trigger a vigorous surface frontal cyclone offshore of the eastern US with its eastern divergence zone… with the surface cyclone potentially acquiring tropical characteristics by days 6 and 7 due to the cold de-stabilizing temps of the upper vorticity… and/or due to the presence of the ribbon of warm Gulf steam waters still running at 26+ deg C offshore of the US mid-Atlantic coast. If other models join the GFS… an area of interest for subtropical development offshore of the eastern US may be declared in the days ahead.


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

1200Z (Oct 20) CMC Model Run…No tropical cyclone formation forecast over the next 7 days (168 hours)

1200Z (Oct 20) ECMWF Model Run... No tropical cyclone formation forecast over the next 7 days (168 hours)

1800Z (Oct 20) GFS Model Run...

**Possible subtropical cyclone formation offshore of the northeastern US coast near 38N-71.5W at 147 hours

1800Z (Oct 20) NAVGEM Model Run... No tropical cyclone formation forecast over the next 7 days (168 hours)

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