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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 OCTOBER 20 2020 2:27 PM EDT...

See Tropical Storm Epsilon section below for the only active tropical cyclone in the Atlantic basin. See area of interest section below for western Caribbean Sea activity being monitored for development.

Elsewhere...a tropical wave of low pressure in the eastern tropical Atlantic is producing a concentrated thunderstorm mass with the aid of upper outflow from an upper ridge in the region. However tropical cyclone development is unlikely here once wind shear increases by 48 hours. This shear will be induced by a fragment of northeastern Atlantic upper vorticity to be pushed southward by the strong warm north Atlantic upper ridge...which will be re-enforced by the latent heat release of Tropical Storm Epsilon and the surface warm southerly flow to occur on the east side of Epsilon.

TROPICAL STORM EPSILON...Epsilon is gradually strengthening while it continues to wrap the thunderstorms once lopsided to the east of the center increasingly over and to the west of the center. This is an indication that the thunderstorm latent heat release warming is weakening the western Atlantic cold core cut-off upper vortex to the west and the string of upper vorticity that has been approaching from the northeast Atlantic upper vortex...features that were previously pushing the thunderstorms to the east. As long as these trends continue and Epsilon's track stays east of the western Atlantic upper will be able to continue to produce expansive warm core outflow in between that vortex and the northeast Atlantic upper vortex...and significant strengthening is on the table. I continue to forecast Epsilon to become a category 2 hurricane before reaching 26 deg C and cooler water by 72+ hours...higher than the 11 AM EDT NHC forecast. Based on the current position of Epsilon and the fact its track is already speeding up to the northwest...the forecast track points are adjusted northward. The short-term northwest track is occurring as Epsilon rounds the east side of the western Atlantic upper vortex. A west angle is kept through 72 hours as a surface ridge will be building to the north under the convergence zone of one of the upper troughs to eject from the central North America upper vortex once that vortex finally breaks up...with a straight north angle shown by 96 hours from a surface ridge weakness to then pass north of Epsilon under the eastern divergence zone of the next upper trough tied to the collapsing North America upper vortex. This next upper trough should curve Epsilon northeastward by 120 hours...with the storm transitioning to a non-tropical remnant frontal cyclone due to the combination of cooler waters which should weaken the thunderstorms and warm core and the supportive divergence zone of the upper trough overspreading Epsilon.

Epsilon has already established warm anticyclonic outflow all the way up to the 200 mb layer of the atmosphere...making it more difficult for Epsilon and its outflow to whirl westward under the western Atlantic upper vortex than if it were a shallower warm core system or subtropical system. This should mean that Epsilon stays east of Bermuda...resulting in less rain and wind impact from Epsilon later this week...but coastal sea swells are definitely on the table. Interest here should watch Epsilon carefully as there is the usual forecast track uncertainty in the longer range...and Bermuda is under a tropical storm watch. Coastal sea swells are also possible for Newfoundland this weekend as Epsilon transitions into a strong non-tropical cyclone potentially located not far offshore.

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

0 Hr Position (1200Z Oct 20)...50 mph maximum sustained wind tropical storm centered at 26.5N-55W

IOH 24 Hr Forecast (1200Z Oct 21)...80 mph maximum sustained wind hurricane centered at 29.5N-57.5W

IOH 48 Hr Forecast (1200Z Oct 22)...100 mph maximum sustained wind hurricane centered well east of Bermuda at 32N-60W

IOH 72 Hr Forecast (1200Z Oct 23)...105 mph maximum sustained wind hurricane centered northeast of Bermuda at 35N-62.5W

IOH 96 Hr Forecast (1200Z Oct 24)...85 mph maximum sustained wind hurricane centered in the northwest Atlantic at 37.5N-62.5W

IOH 120 Hr Forecast (1200Z Oct 25)...Non-tropical remnant frontal cyclone centered south of Newfoundland at 42N-56W

AREA OF INTEREST #1....The rather large and broad surface low pressure field in the western Caribbean Sea remains poorly organized while producing scattered squalls of showers and thunderstorms that span from Cuba and the eastern Gulf of Mexico all the way to the southern Caribbean...all while lacking a well-defined center. Based on the latest satellite could be argued there is one broad center over the northeastern Yucatan peninsula supported by the divergence zone of a shortwave upper trough moving around the central North America upper vortex...and another broad center toward the southern Caribbean near 15N-78W. Therefore for my updated outlook below...I initialize this system in between at 15N-80W and forecast from there. My best guess is that if consolidation were to would happen around 17N latitude where the outflow of the upper ridge axis is centered in the longer range on the 1200Z GFS model run. I have 0% odds of development in the short term to give time for this sprawling system to consolidate...and I keep odds of development at a low 10% in the long term as there is no guarantee that this system will consolidate enough to become a tropical cyclone.

On a final note...if this system were to consolidate within the next five would drift westward under the influence of persistent surface ridging to the north. Therefore statements for the Yucatan peninsula region...including regards to this system are on the home page bulletins of this site. Odds are dropped back to 0% by 96 hours with the current forecast track increasing the land interaction with the Yucatan peninsula by that time. It is interesting to note that recent CMC...GFS...and NAVGEM runs in the model summary section below now show consolidation occurring late in the five day forecast period and toward the Cayman Islands and Cuba...perhaps from the current broad center near 15N-78W pivoting northward around the other current broad center over the northeastern Yucatan and becoming the dominant center. If this were to occur...would have to notably shift the forecast points in future outlooks further to the east and add the Cayman Islands and Cuba to the home page bulletins.

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

IOH 24 Hr Outlook (1200Z Oct 21)...0% chance of tropical cyclone formation (western Caribbean Sea near 16N-82W)

IOH 48 Hr Outlook (1200Z Oct 22)...0% chance of tropical cyclone formation (western Caribbean Sea near 17N-84.5W)

IOH 72 Hr Outlook (1200Z Oct 23)...10% chance of tropical cyclone formation (just offshore of the Belize/Mexico border near 17N-87W)

IOH 96 Hr Outlook (1800Z Oct 24)...0% chance of tropical cyclone formation (Belize/Mexico border near 17N-88.2W)


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

0000Z CMC Model Run...For Tropical Storm Epsilon...gradually strengthens and passes east of Bermuda at 72 hours...reaches 38N-58.5W at 120 hours. For area of interest #1...northwestern lobe of broad low pressure gradually moves west-northwest across southern Gulf of Mexico without tropical cyclone formation...northeastern lobe consolidates at a location between Florida and Cuba at 126 hours but also does not develop in the long range while it too drifts westward.

0000Z ECMWF Model Run...For Tropical Storm Epsilon...gradually strengthens and passes east of Bermuda between 72 and 96 hours...reaches 36.5N-61W at 120 hours. For area of interest tropical cyclone formation shown.

1200Z GFS Model Run...For Tropical Storm Epsilon...gradually strengthens and passes east of Bermuda at 60 hours...reaches 39.8N-55W at 120 hours while accelerating northeastward. For area of interest #1...consolidates south of the Cayman Islands at 126 hours...consolidated circulation moves westward toward the Yucatan peninsula in the long range.

0600Z NAVGEM Model Run... For Tropical Storm Epsilon...gradually strengthens while

passing just east of Bermuda at 78 hours...accelerates northeastward and reaches 39.8N-53.5W at 120 hours. For area of interest #1...northwestern lobe of broad low pressure gradually moves west-northwest across southern Gulf of Mexico without tropical cyclone formation...southern lobe of low pressure drifts northward while pivoting around the northwestern lobe and consolidates between Cuba and the Cayman Islands at 126 hours...consolidated circulation moves northwestward into the eastern Gulf of Mexico while tropical cyclone formation suggested in the long range.

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