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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.**********  

...WEDNESDAY OCTOBER 21 2020 10:40 PM EDT...

See Hurricane 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 divergence between the northeast Atlantic upper trough and a tropical upper ridge axis to the south. However tropical cyclone development is unlikely in the short term as wind shear is increasing. This shear is being induced by a fragment of northeastern Atlantic upper trough getting pushed southward by the strong warm north Atlantic upper ridge...which is being re-enforced by the latent heat release of Hurricane Epsilon and the surface warm southerly flow occurring on the east side of Epsilon. However in a few days the tropical wave may reach a lower shear environment in the central tropical Atlantic...with the CMC and NAVGEM models suggesting development here. Will see the state of this tropical wave after it exits the high shear environment in consideration of whether or not to upgrade it to area of interest status.

MAJOR HURRICANE EPSILON...Epsilon stuns while rapidly intensifying into a minimal category 3 hurricane over the last 24 hours...even my previous forecasts which have been higher than the NHC and predicting category 2 strength were not enough. I did not expect higher than category 2 status as Epsilon is moving toward 26 deg C and cooler

water. Another negative thermodynamic factor is the dry air generated by the western convergence zone of the western Atlantic upper vortex that Epsilon has been interacting with...which has been ingested into the hurricane such that the thunderstorm intensity on colorized infrared satellite pictures is not what is typically seen in a category 3...and the thunderstorm bands around the core of the large hurricane are broken up rather than making a solid shield around the core. Because the thunderstorm intensity is not as strong as is typical for a major hurricane...I speculate the strengthening to this level has been boosted by divergence in the northeast quadrant of the western Atlantic upper vortex which is what we see in non-tropical addition to the expansive warm core outflow between the upper vortex and northeast Atlantic upper trough that has provided strengthening by tropical means. The size of the aforementioned upper outflow and upper divergence fields has dropped surface pressures over a large area such that Epsilon’s outer circulation and its tropical storm force wind field has been made quiet large.

The hurricane has also whirled more westward into the western Atlantic upper vortex than I previously projected...thus my short-term forecast points have been adjusted westward. Perhaps the hurricane and it’s central warm core outflow has been able to fit under the upper vortex while the thunderstorm intensity (and hence latent heat release) weakened from the dry air mentioned in the previous paragraph...thus making the vertical warm core structure more shallow. A west angle is kept in the forecast track through 48 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 collapsing central North America upper vortex. Although I raise the short term intensity forecast...the longer term forecast is kept the same as the 1200Z GFS suggested Epsilon’s western outflow will be fighting with residual upper vorticity to the west to be left behind by the western Atlantic upper vortex...and also because the hurricane will be moving toward cooler water. A turn to the northeast is shown by 72 hours from a surface ridge weakness to be induced under the eastern divergence zone of the next upper trough tied to the collapsing North America upper vortex. By 96 hours the hurricane should transition 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 aforementioned next upper trough overspreading Epsilon. Because the models show a faster northeast track...the longer term track forecast is kept the same despite the initial west adjustment of the short term track forecast.

Interests in Bermuda by tomorrow night and Friday will experience the west and south sides of Epsilon’s outer circulation containing gusty winds on the updated forecast track...power outages are possible here in addition to coastal sea swells. Coastal sea swells are also likely for Newfoundland this weekend as Epsilon transitions into a strong non-tropical cyclone located not far offshore.

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

0 Hr Position (1800Z Oct 21)...115 mph maximum sustained wind major hurricane centered at 29.6N-60W

IOH 24 Hr Forecast (1800Z Oct 22)...105 mph maximum sustained wind hurricane centered east of Bermuda at 32N-62W

IOH 48 Hr Forecast (1800Z Oct 23)...95 mph maximum sustained wind hurricane centered north of Bermuda at 35N-64W

IOH 72 Hr Forecast (1800Z Oct 24)...85 mph maximum sustained wind hurricane centered in the northwest Atlantic at 37.5N-63W

IOH 96 Hr Forecast (1800Z Oct 25)...Non-tropical remnant frontal cyclone centered south-southeast of Newfoundland at 43N-55W

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 over Cuba...Jamaica...and the Cayman Islands...all while lacking a well-defined center. The 1800Z NHC TAFB surface analysis agrees with the observation from yesterday that there is one broad center over the northeastern Yucatan peninsula...and another broad center toward the southern Caribbean offshore of Nicaragua and Honduras. Models have continued to show the southern broad center pivoting northward around the Yucatan center...arriving to Cuba...the Cayman Islands...and perhaps south Florida and the western Bahamas...with the potential for this center to become the dominant and possibly evolve into a tropical cyclone. It appears the catalyst for this center to slightly strengthen and become the dominant by 96 hours is the divergence zone of a current southwest US shortwave upper trough to arrive...but this shortwave may also disrupt the organization by introducing wind shear. 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...and also due to the possible burst of shear at 96 hours. In the outlook below...the northward drift of this disturbance is slightly quickened by 120 hours due to the approach of a frontal system and more substantial upper trough to approach from the western and central US. The forecast track shift for this disturbance has caused the introduction of the Cayman Islands...Cuba...south Florida...and the western Bahamas on the home page bulletin of this site tied to this disturbance.

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

IOH 24 Hr Outlook (1800Z Oct 22)...0% chance of tropical cyclone formation (south of the Cayman Islands near 17N-82W)

IOH 48 Hr Outlook (1800Z Oct 23)...0% chance of tropical cyclone formation (just south of the Cayman Islands near 18N-82W)

IOH 72 Hr Outlook (1800Z Oct 24)...10% chance of tropical cyclone formation (the Cayman Islands near 19N-82W)

IOH 96 Hr Outlook (1800Z Oct 25)...10% chance of tropical cyclone formation (the Cayman Islands near 20N-82W)

IOH 120 Hr Outlook (1800Z Oct 26)...10% chance of tropical cyclone formation (south coast of western Cuba near 22N-82W)


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

1200Z CMC Model Run...For Hurricane Epsilon...passes east of Bermuda at 36 hours...accelerates rapidly into the open North Atlantic and merges with another frontal cyclone by 120 hours. For area of interest #1...northeastern lobe of broad low pressure consolidates at a location between Florida and the western Bahamas at 96 hours....tropical cyclone formation suggested over the northwest Bahamas at 108 hours...moves northeast and reaches 27.5N-76W at 120 hours. Elsewhere...currently vigorous tropical wave at 34W longitude develops into possible tropical cyclone at 9N-50W at 54 hours...weakens back to a tropical wave near 55W longitude by 78 hours.

1200Z ECMWF Model Run...For Hurricane Epsilon...passes east of Bermuda at 48 hours...accelerates rapidly into the open North Atlantic and merges with another frontal cyclone by 120 hours. For area of interest #1...northeastern lobe of broad low pressure consolidates at a location between Florida and the western Bahamas at 96 hours....however no tropical cyclone formation suggested as the consolidated circulation moves northeast into the open western Atlantic.

1200Z GFS Model Run... For Hurricane Epsilon...passes east of Bermuda at 36 hours...accelerates rapidly into the open North Atlantic and merges with another frontal cyclone by 120 hours. For area of interest tropical cyclone formation shown.

1200Z NAVGEM Model Run...For Hurricane Epsilon...passes east of Bermuda at 36 hours...accelerates rapidly into the open North Atlantic and reaches 51N-38W as a large and intense remnant frontal cyclone. For area of interest #1...broad low pressure consolidates just west of the Cayman Islands and south of western Cuba at 54 hours...the consolidated circulation elongates into a surface trough that spans from western Cuba to the western Atlantic by 120 hours...possible development on east end of surface trough at a location west of Bermuda in the long range. Elsewhere...currently vigorous tropical wave at 34W longitude develops into a low pressure spin at 9N-55W at 66 hours and crosses the southern Lesser Antilles at 102 hours...possible tropical cyclone formation in the southern Caribbean shown in long range.

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