top of page
Home: Text


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 

Home: Text
Home: Blog2
  • Writer's pictureNCHurricane2009


*******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 SEPTEMBER 29 2020 1:08 PM EDT...

See area of interest #1 section below for the tail end of a cold front currently heading toward the western Caribbean Sea from the Gulf of Mexico being monitored for possible tropical cyclone formation over the next few days.

Various long range runs of the NAVGEM and ECMWF over the last few days have suggested a tropical wave of low pressure may emerge from western Africa and develop in the eastern tropical Atlantic underneath a favorable upper ridge to persist over the region by next week...therefore in addition to area of interest #1 may have to also watch this region in the coming days.

And finallly...the tropical wave of low pressure currently in the open Atlantic near 45W longitude may amplify (intensify) in a regime of split flow upper divergence upon entering the eastern or central Caribbean Sea in a few days. This upper air pattern will occur if the current north Atlantic upper vorticity dives southward toward the eastern Caribbean Sea due to the expansion of the northwestern Atlantic upper ridge to be induced by the warm sector of the current frontal system over the eastern US...with the split upper level flow occuring between the southwest side of the upper trough and southeast side of the Caribbean upper ridge to build over area of interest #1. The split flow upper divergence could result in the tropical wave intensifying into a possible eastern or central Caribbean Sea tropical cyclone to the east of area of interest #1 by next week. Or alternatively if area of interest #1 does not consolidate and develop early...the strengthening tropical wave could merge with area of interest #1...resulting in a large and broad tropical disturbance in the western Caribbean Sea.

AREA OF INTEREST #1...High-amplified upper trough energy over central North America is driving a surface cold front across the eastern United States and Gulf of Mexico...and the tail end of this cold front is expected to reach the western Caribbean Sea over the next day or so. In 3 to 4 days...upper-level winds over the western Caribbean will become more conducive for tropical development as the central North America upper trough regime relaxes...allowing an upper ridge with low shear and upper outflow to expand in the trough regime's wake...therefore watching to see if the tail end of the front evolves into a tropical disturbance in the western Caribbean Sea. I have raised my peak odds of tropical cyclone formation over the next 5 days further to 60%...slightly higher than the latest NHC tropical weather outlook...due to the favorable upper-level wind outlook and as all of the model runs at this point at least depict a closed surface tropical circulation developing in the western Caribbean Sea. In addition there is already an ample amount of thunderstorm activity with the cold front in the western Gulf of Mexico. I have shifted my forecast points in the outlook below further south towards the currently heavier thunderstorm activity along the front...and have now included the east coast of Belize in the home page bulletins concerning this disturbance. Any tropical cyclone that does form will likely move initially west around the south side of the strong surface ridge currently building over North America and supported by the western convergence zone of the developing central North America upper trough regime...with an increasing north bend in track with time possible should this system become a strong/tall enough tropical cyclone to be guided by upper southwesterly flow ahead of a shortwave upper trough to pivot southeastward around the west side of the central North America upper trough regime and toward the Gulf of Mexico and southeastern United States. Due to the forecast 120 hours I drop development odds below the 60% peak due to potential land interaction with the Yucatan peninsula and a possible increase in southwesterly shear from the aforementioned shortwave upper trough.

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

IOH 24 Hr Outlook (1200Z Sep 30)...0% chance of tropical cyclone formation (east coast of the Yucatan peninsula near 20N-86.5W)

IOH 48 Hr Outlook (1200Z Oct 1)...0% chance of tropical cyclone formation (western Caribbean Sea near 19N-85W)

IOH 72 Hr Outlook (1200Z Oct 2)...20% chance of tropical cyclone formation (western Caribbean Sea near 19N-85W)

IOH 96 Hr Outlook (1200Z Oct 3)...60% chance of tropical cyclone formation (east coast of the Yucatan peninsula near 20N-87W)

IOH 120 Hr Outlook (1200Z Oct 4)...40% chance of tropical cyclone formation (northwest corner of Yucatan peninsula near 21N-90W)


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

0000Z CMC Model Run...For area of interest #1...surface low consolidates just east of the Belize/Mexico border at 96 hours...while stationary surface low becomes larger and broader while spanning much of the western Caribbean Sea by 150 hours.

0000Z ECMWF Model Run....For area of interest #1...surface low consolidates west of the Cayman Islands and south of western Cuba at 96 hours...moves west-northwest into the Yucatan channel waters between western Cuba and the northeastern corner of the Yucatan peninsula by 120 hours.

0600Z GFS Model Run...For area of interest #1...surface low consolidates just offshore of Honduras at 84 hours...tropical cyclone formation suggested at 90 hours...makes landfall as a compact and strengthening tropical cyclone near the Belize/Mexico border at 102 hours...arrives to the west coast of the Yucatan peninsula as a weakened tropical cyclone at 120 hours.

0600Z NAVGEM Model Run...For area of interest #1...large and broad surface low develops in the western Caribbean Sea at 102 hours...moves slowly northwestward into Gulf of Mexico while gradually developing into a large and weak tropical cyclone in the long range. Elsewhere...tropical wave currently near 45W longitude becomes better defined just south of Puerto Rico at 96 hours...tropical cyclone formation suggested just northeast of the Dominican Republic at 126 hours.

47 views0 comments


bottom of page