BIRDSEYE VIEW POSTS

Since 2012 on the Weather Underground (www.wunderground.com) 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 via Disqus on Weather Underground at www.wunderground.com/cat6. You can see my Disqus feed at this link for my latest comments. Feel free to reply to me with your disqus account or e-mail at IOHurricanes@outlook.com 

 
 
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MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #178

*******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 media...watches 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.gov (hurricanes dot gov) for the latest watches/warnings and official forecasts on active tropical cyclones.**********  


...THURSDAY NOVEMBER 12 2020 8:08 PM EDT...



See Tropical Storm Eta and Tropical Storm Theta sections below for an update on the two currently active tropical cyclone in the Atlantic basin. See area of interest section below for a tropical wave of low pressure currently in the central Caribbean Sea being monitored for tropical development.


TROPICAL STORM ETA...Early this morning...Eta made landfall on the northwest Florida peninsula coast as a 50 mph maximum sustained wind tropical storm. This was a notably lower intensity from its category 1 hurricane intensity it achieved in the eastern Gulf of Mexico...as the circulation continued to lack thunderstorm activity. Since the landfall...Eta has been moving faster to the northeast compared to previous forecasts and has already moved back into the western Atalntic from northeastern Florida...and is in fact already passing offshore of Georiga. As a result...the models and forecast track have shifted north and east. It is also surprising that Eta still is at tropical storm strength...albiet just barely while now at 40 mph maximum sustained winds. This is probably due to the support of divergent upper westerly flow between the western Atlatnic deep-layered ridge to the east and fast-approaching southern Canada upper trough to the northwest. Eta is becoming increasingly entangled with a cold front originating from the central US that is now arriving to the US east coast...and thus will continue northeast through the narrow surface ridge weakness tied to this front. The models are in strong agreement that Eta will transition into a remnant low along this front in the next 24 hours...especially as the front becomes re-enforced by the approach of the cold southern Canada upper trough. After 24 hours...Eta is forecast to lose its identity to a much stronger frontal cyclone to form further north along the same front in the upper divergence maximum of the upper trough.

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

0 Hr Position (1800Z Nov 12)...40 mph maximum sustained wind tropical storm centered just offshore of Georgia at 31.6N-80.6W

IOH 24 Hr Forecast (1800Z Nov 13)...Remnant frontal low pressure centered offshore of the eastern United States coast at 35.5N-73W

TROPICAL STORM THETA...Theta's vertical warm core has grown taller in the last 24 hours as the GFS model upper-level wind field in the above birdseye view chart...plotted all the way up at the 200 mb layer of the atmosphere...has some anticyclonic curvature which is characteristic of the wamr core upper outflow induced by thunderstorms. The stronger warm core is an indication of yesterday's thunderstorm flare helping Theta...and the tropical storm is a little stronger today while having 65 mph maximum sustained winds. Even with the aid of the eastern divergence zone of the central Atlantic upper trough...Theta today is struggling to produce thunderstorms in what is a less than ideal thermodynamic setting....specifically with water temps below 26 deg C and upper air temps that are also not not particularly cold (in the vicinity of Theta...the 200 mb height is 1212 dekameters...would like to see heights toward 1200 or less for cold enough upper air temps for instability at cooler water temps). Therefore I forecast Theta to transition to a non-tropical frontal cyclone supported by the central Atlantic upper trough in the next 24 hours. However I maintain a forecast on Theta for some after that in case the NHC and models are correct in Theta holding on to tropical status for longer.

Updated forecast track is shifted slightly eastward due to the current position of Theta...and in the short-term Theta should continue eastward in tandem with its supporting central Atlantic upper trough. By 48 and 72 hours the upper trough is forecast to elongate into a strip of upper vorticity due to the strength of the deep-layered ridge to the west...and I forecast Theta to stall west of the Canary Islands by that time in between conflicting steering of the deep-layered ridge and a surface ridge forecast to be over Europe to the east. I also forecast weakening to occur due to possible exposure to a lack of divergence beneath the upper vorticity and eastern upper convergence zone of the deep-layered ridge. I have ended the forecast at 72 hours as I am more confident in Theta weakening by then. After 72 hours...it appears for now that whatever is left of Theta will be pulled northward into a large north Atlantic frontal cyclone to later develop with the support of the current southern Canada upper trough as that trough moves into the north Atlantic.

Regardless of whether or not Theta retains tropical characteristics in the longer range...this system will pass near enough to the Azores and Canary Islands to produce coastal sea swells. The Canary Islands may see gusty winds from this system in a few days should the long term track forecast be adjusted eastward.

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

0 Hr Position (1800Z Nov 12)...65 mph maximum sustained wind tropical storm centered at 31.7N-27.4W

IOH 24 Hr Forecast (1800Z Nov 13)...60 mph maximum sustained wind frontal cyclone centered at 31.5N-22.5W

IOH 48 Hr Forecast (1800Z Nov 14)...Frontal low centered west of the Canary Islands at 31.5N-20W

IOH 72 Hr Forecast (1800Z Nov 15)...Frontal low centered west of the Canary Islands at 31.5N-20W

AREA OF INTEREST #1...The central Caribbean surface low pressure has essentially been nearly stationary over the last day while evolving into a surface low pressure spin supported by an area of upper divergence between the east side of a southern Caribbean upper ridge cell and west side of the central Atlantic upper trough tied to Tropical Storm Theta. The spin has thunderstorm activity that has been scattered and slowly organizing thus far...perhaps from some disruption of a southwest-northeast upper trough axis forming over the north side of this disturbance as the southeastern Gulf of Mexico upper trough is linking with the southwest end of the central Atlantic upper trough. However this disturbance is already more consolidated and organized than I previously anticipated considering the disruption of the upper trough...and the models are unanimous in showing tropical cyclone formation. Therefore I have begun a tropical cyclone formation forecast as outlined below.

Forecast westward track is slow for the first 24 hours due to the surface ridge weakness created by Tropical Storm Eta...followed by some increase in forward speed by 48 hours from an eastern US surface ridge to build in the wake of Eta and southern Canada upper trough to exit the region. By 72+ hours... the current upper vorticity over southern Alaska is forecast to arrive into the eastern North America as a strong upper trough whose eastern divergence zone creates a strong frontal cyclone and whose western convergence zone creates a strong surface ridge over the south-central United States. The forecast position of the frontal cyclone is too far north to influence the steering...therefore it is likely in the longer term that this system’s westward track continues but remains slow due to the blocking effect of the forecast south-central United States surface ridge...potentially bending on a southward angle from the strength of the surface ridge as this system moves into Nicaragua and eastern Honduras.

The southwest-northeast weak upper trough crossing through the north half of this disturbance should be gradually weakening from the latent heat release of the disturbance’s thunderstorms...therefore the upper outflow of this disturbance should improve with time. I forecast slow strengthening for the first 48 hours to give time for the upper trough to dissipate....followed by rapid strengthening given the favorable upper wind outlook... strong computer model support...and warm Caribbean waters. My intensity forecast brings this system to category 1 hurricane strength by 72 hours...and it is possible that category 2 strength is reached before landfall in Nicaragua and Honduras.

Needless to say...this forecast is terrible news as we are likely in for tropical cyclone impacts in Nicaragua and Honduras only recently after Hurricane Eta devastated this region with powerful winds and catastrophic rainfall flooding...and unfortunately interests here need to be aware of this disturbance. Northern rain bands of this system may produce heavy rainfall over Jamaica over the next couple of days.

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

0 Hr Position (1800Z Nov 12)...Surface low pressure centered in the central Caribbean Sea at 15N-72.5W

IOH 24 Hr Forecast (1800Z Nov 13)...Surface low pressure centered south-southeast of Jamaica at 15N-75.5W

IOH 48 Hr Forecast (1800Z Nov 14)...50 mph maximum sustained wind tropical storm centered southwest of Jamaica at 15N-79W

IOH 72 Hr Forecast (1800Z Nov 15)...85 mph maximum sustained wind hurricane centered just offshore of the Nicaragua/Honduras border at 15N-81.5W

IOH 96 Hr Forecast (1800Z Nov 16)...50 mph maximum sustained wind tropical storm centered over northeastern Nicaragua at 14N-84W

IOH 120 Hr Outlook (1800Z Nov 17)...Remnant low pressure centered over the western Nicaragua/Honduras border at 13N-86.5W

..COMPUTER MODEL SUMMARY...

Source...Florida State University Experimental Forecast Tropical Cyclone Genesis Potential Fields (http://moe.met.fsu.edu/tcgengifs/)

1200Z CMC Model Run... For Tropical Storm Eta...transitions to elongated remnant frontal low offshore of North Carolina at 35N-72.5W at 36 hours. For Tropical Storm Theta...stalls west of the Canary Islands at 31N-20W from 60 to 90 hours while weakening...circulation weakens to a remnant trough at 35N-20W at 108 hours. For area of interest #1...tropical cyclone formation suggested just offshore of the Nicaragua/Honduras border at 15N-81.5W at 66 hours...makes landfall at border at 78 hours...weakens to a remnant low over central Honduras at 102 hours.

1200Z ECMWF Model Run...For Tropical Storm Eta...transitions to elongated remnant frontal cyclone of the Carolinas just 24 hours. For Tropical Storm Theta...stalls just west of the Canary Islands around 72 hours while beginning to weaken...circulation then tracks northwest and then northeast and weakens to a remannt surface trough north of the Canary Islands by 120 hours. For area of interest #1...tropical cyclone formation suggested at 15N-75.5W at 48 hours...begins to strengthen briskly as a compact tropical cyclone by 72 hours while located at 15N-79.5W...makes landfall on the Nicaragua/Honduras border as a compact and strong hurricane just after 96 hours...rapidly weakens to an inland remnant low at the central Nicaragua/Honduras border by 120 hours.

1200Z GFS Model Run...For Tropical Storm Eta...transitions to elongated remnant frontal low offshore of North Carolina at 35.5N-73.5W at 30 hours. For Tropical Storm Theta...stalls west of the Canary Islands at 30.5N-20W from 72 to 84 hours while beginning to weaken...circulation weakens further while passing north of the Canary Islands by 126 hours. For area of interest #1...tropical cyclone formation suggested at 14.5N-77.5W at 66 hours...becomes a compact and intense tropical cyclone centered just offfshore of northeastern Honduras by 108 hours...intense tropical cyclone drifts southwestward into eastern Honduras by 126 hours.

1200Z NAVGEM Model Run...For Tropical Storm Eta...transitions to elongated remnant frontal low offshore of Virginia at 36.5N-73.5W at 30 hours. For Tropical Storm Theta...reaches waters west of the Canary Islands at 31.5N-20.5W at 60 hours...circulation weakens to a remnant surface trough at 40N-16.5W at 102 hours. For area of interest #1...tropical low pressure cyclone formation suggested just southwest of Jamaica at 17.5N-79.5W at 72 hours...by 120 hours becomes a strong hurricane approaching the east coast of the Yucatan peninsula of Mexico.

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