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 #171

*******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 5 2020 11:43 AM EDT...

See Tropical Depression Eta section below for the only active tropical cyclone in the Atlantic basin. Elsewhere...a deep-layered low pressure consisting of a broad surface spin and upper-level vortex located to the west of Portugal and Spain and north of the Canary Islands is able to produce showers and thunderstorms over 20 deg C waters due to the rather cold temperatures of the upper vortex. However the current northwestern Atlantic frontal system and upper trough will soon lift this system northward into even cooler waters...with the large divergence zone of the upper trough keeping the surface circulation broad without a tight center needed for subtropical cyclone formation. Subtropical cyclone development here is not expected.


TROPICAL DEPRESSION ETA...While continuing westward further inland into Honduras...Eta has weakened from a tropical storm to a minimal tropical depression. It could be argued that Eta has degenerated into a remnant low pressure while lacking the traditional well-defined spin of a tropical cyclone...but I believe the National Hurricane Center is continuing advisories on Eta as a tropical depression as the models are now in strong agreement that Eta will soon regenerate a center offshore of Honduras in the strong offshore thunderstorm bands being supported by the outflow of an upper ridge cell over the Caribbean...as well as the divergent upper flow between the northeast side of the upper ridge and southeast side of the cut-off upper trough currently over the southeastern United States. Unlike my previous updates...my forecast below has been updated to show Eta's remnant low regenerating into a tropical cyclone given the National Hurricane Center's handling of the situation where the name Eta will be continued as the original surface circulation broadens and fizzles out over Honduras while a new center tightens up offshore in the aforementioned thunderstorm bands that have upper-level atmospheric support. The cut-off upper trough over the southeastern United States responsible for the upper-level atmospheric support will soon amplify while re-enforced by incoming upper vorticity currently over the central United States...resulting in some decrease in shear and an increase in upper-level divergence that will allow for Eta's forecast new center to re-intensify into a tropical storm while also pushing Eta east-northeastward into the Cayman Islands and Cuba by 48 to 72 hours. I am in agreement with the NHC's 10 AM EDT intensity forecast showing gradual instead of rapid strengthening as the size of the upper-level divergence field should cause Eta to become a large/broad tropical storm with a lax pressure gradient between its center and outer edge...thus keeping max sustained winds lower. Eta during this time should also have a large comma shaped thunderstorm mass lopsided to the northeast of the center as we see with tropical systems that are supported by a cold core cut-off upper trough...a characteristic that could make Eta more of a subtropical system instead of a fully tropical one.


In the long range (96+ hours)...deep-layered ridging will build over the eastern United States...to the north of Eta and the cut-off upper trough. At the surface...a strong ridge over the eastern United States will be supported by the western convergence zone of the current upper trough moving across central Canada...once that trough enters the northwest Atlantic. A strong surface frontal system/upper trough to trek over the western and central US will advect plenty of warm air northward to induce an upper-level ridge over the eastern United States...which will cause the cut-off upper trough to amplify into an upper vortex. The upper vortex will likely make Eta look more subtropical by 96 hours...and in combination with the deep-layered eastern United States ridging should whirl Eta northwestward from Cuba and the western Bahamas and into south Florida and/or the Florida Keys. I keep a slight northward angle in track through 120 hours as the vigorous frontal system/upper trough over the central United States may slightly weaken the eastern United States deep-layered ridging...but much of the model guidance indicates in the long range that Eta will continue mainly west into the southeastern Gulf of Mexico as the frontal system will likely not induce enough of a ridge weakness to recurve Eta northward. By 120 hours...Eta should become more tropical in nature once the cold core upper vortex weakens from the continued latent heat release of Eta's thunderstorms and as the upper vortex remains cut-off from high latitude cold air to the south of the deep-layered ridging. However I agree with the NHC which shows only slow strengthening during that time...due to a high chance of land interaction with the southern Florida peninsula. After 120 hours...Eta could very well become a hurricane in the southeastern Gulf of Mexico after clearing Florida and once the upper vortex diminishes further...an idea the 0600Z GFS and 0000Z ECMWF agreed on.


Belize is experiencing heavy rainfall from a band of thunderstorms on the northwest side of Eta's circulation...flash flooding remains possible here. I recommend interests in the Cayman Islands...Cuba...and the western Bahamas to begin preparing for tropical storm conditions (heavy rain...gusty winds with some damage potential...coastal storm surge) to arrive by Saturday and Sunday. I also recommend interests in south half of the Florida peninsula and the Florida Keys to gather storm preparation supplies early to avoid last minute public crowding amid the COVID-19 virus outbreak as conditions will likely deteriorate by late Sunday or Monday. If you live in an area prone to coastal storm surge impacts...think of a family/friend residence or a hotel you can relocate to in case you may have to do so in the coming days...as a public storm shelter may not be as ideal in controlling your exposure to COVID-19. Because Eta will likely transition into a large and sprawling system as it interacts with the cut-off upper trough to the north...heavy rain bands could spread as far east as Jamaica...Haiti...and the central and eastern Bahamas in the coming days.

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

0 Hr Position (1200Z Nov 5)...30 mph maximum sustained wind tropical depression centered over Honduras at 14.5N-87W

IOH 24 Hr Forecast (1200Z Nov 6)...Remnant low pressure centered offshore of Honduras at 16.2N-86.5W

IOH 48 Hr Forecast (1200Z Nov 7)...45 mph maximum sustained wind tropical storm centered just west of Grand Cayman Island at 19N-82.5W

IOH 72 Hr Forecast (1200Z Nov 8)...50 mph maximum sustained wind tropical storm centered over central Cuba at 22.5N-79W

IOH 96 Hr Forecast (1200Z Nov 9)...60 mph maximum sustained wind tropical storm centered just west of Andros Island of the western Bahamas at 24N-79W

IOH 120 Hr Forecast (1200Z Nov 10)...65 mph maximum sustained wind tropical storm centered over the Florida Keys at 24.5N-81W


...COMPUTER MODEL SUMMARY...

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


0000Z CMC Model Run...For Tropical Depression Eta...weakens to a remnant low by 6 hours...remnant low moves northwestward to east coast of Belize in 36 hours...while accelerating northeastward regenerates into a tropical cyclone while crossing the Cayman Islands by 78 hours...crosses central Cuba by 108 hours...turns westward while tracking along the north coast of Cuba by 120 hours.


0000Z ECMWF Model Run...For Tropical Depression Eta...weakens to a remnant low over Honduras in the next 24 hours...remnant low lifts northwestward to waters just offshore of Belize by 48 hours...accelerates northeastward into Grand Cayman Island while regeneratng into a tropical cyclone by 72 hours...crosses central Cuba by 96 hours...turns westward along north coast of Cuba and by 120 hours begins to quickly intensify just north of the western Cuba coast at 120 hours.


0600Z GFS Model Run...For Tropical Depression Eta...weakens to a remnant low over Honduras by 6 hours...remnant low lifts northward into western Caribbean Sea from Honduras by 24 hours...remnant low regenerates into a tropical cyclone near 19N-85W at 30 hours...turns eastward into the Cayman Islands by 60 hours...crosses central Cuba by 84 hours...turns westward along north coast of Cuba through 114 hours...begins to quickly intensify in southeastern Gulf of Mexico offshore of the western Cuba coast in the long range.


0600Z NAVGEM Model Run...For Tropical Depression Eta...weakens to a remnant low by 6 hours with remnant low establishing a tighter center along the north coast of Honduras...remnant low strengthens offshore offshore of Belize by 36 hours...remnant low regenerates into a tropical cyclone near 17.5N-85.5W at 48 hours...tropical cyclone continuously strengthens while moving east-northeastward across the Cayman Islands at 66 hours...additional strengthening occurs before tropical cyclone makes landfall over central Cuba by 78 hours...curves northward into the western Bahamas as a strong hurricane by 96 hours...begins to curve more westward in track toward south Florida while strengthening into an intense hurricane by 120 hours.

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