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 #169

*******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.**********


...TUESDAY NOVEMBER 3 2020 3:24 PM EDT...

See Hurricane Eta section below for the only active tropical cyclone in the Atlantic basin. Elsewhere...thunderstorms have notably increased in the open eastern tropical Atlantic in the vicinity of 7.5N-35W...induced by the convergence of a surface tropical wave of low pressure and upper-level divergence on the east side of cut-off upper vorticity that has been persistent in the region. However tropical cyclone formation here is not expected as the current upper trough over eastern North America will leave behind upper vorticity that moves toward the region and increases wind shear in the area further.


MAJOR HURRICANE ETA...According to the NHC 10 AM EDT advisory...Eta last night was stopped from achieving category 5 status due to an eye wall replacement cycle...but has remained a catastrophic category 4 hurricane that has drifted southward just off the coast of northern Nicaragua over the last several hours. This has unfortunately prolonged damaging tropical storm and hurricane force winds and coastal storm surge over eastern Honduras and northeastern Nicaragua. The southward drift has been due to the blocking effect of the strong surface ridge over the southeastern United States...but there are early signs on satellite animation of the eye finally turning westward and crossing the Nicaragua coast. A westward motion taking Eta well inland is expected as the surface ridge gets out of the way while beginning to pass to the north. My short-term track forecast points are shifted south and east due to the current position of Eta which has taken forever to make landfall...and my intensity forecast now keeps Eta as an inland tropical depression instead of a remnant low pressure for the better part of tomorrow November 4 as the delayed landfall has also delayed Eta's inevitable post-landfall weakening.


All models are now in good agreement that Eta's westward track inland will remain slow...and then reverse on a northeast track back over water such that Eta reforms as a tropical cyclone in the western Caribbean Sea. This is expected as the current eastern North America upper trough leaves behind a cut-off trough in the vicinity of Florida over the next couple of days...to be re-enforced by the current upper vorticity over the southwestern US as that vorticity later slides eastward into the southeast US. This cut-off upper trough’s eastern divergence zone is forecast to lower surface pressures to the southeast of the blocking southeast US surface ridge and to the northeast of Eta...with this low pressure field potentially drawing Eta back northeastward instead of allowing Eta to continue west around the surface ridge. Therefore my forecast remains extended thru 5 days to track what will be the remnant low of Eta...in preparation for issuing probability outlooks on the remnants of Eta once Eta weakens to a remnant low after landfall. I forecast a slow westward drift of Eta's remnant low thru 48 hours as Eta rounds the south side of the southeastern US surface ridge while the surface low pressure field to the northeast slows its progress around the ridge. My forecast track during this time stays south of the 1200Z GFS as I do not think the surface low pressure field and cut-off upper trough will be strong enough to bend the track of Eta's remnant low northward...and this has long term consequences in my current projection. It is not until 72+ hours that I drag Eta into the western Caribbean Sea...as this is when the cut-off upper trough and resulting surface low pressure field intensifies due to the arrival of the energy from the southwestern US. Because the 1200Z GFS had an earlier northward turn than I forecast...it intensifies Eta itself in the eastern divergence zone of the strengthening cut-off upper trough as a tropical or subtropical cyclone. But with my further south initial track forecast...I forecast the remnant low of Eta to more sharply bend eastawrd in track around the south side of the strengthening suface low pressure field which could very well become its own tropical/subtropical disturbance to the north of Eta if things play out this way. This is also why I held off on explicitly showing tropical cyclone reformation in my forecast unlike the NHC does...in case we end up in a scenario where Eta's remnant and seperate subtropical/tropical disturbance to the north end up competing with each other for low-level inflow/upper outflow.


Interests in northeastern Nicaragua and eastern Honduras should remain hunkered down for ongoing damaging wind and coastal storm surge impacts until Eta moves inland and finally weakens. Severe rainfall flooding is expected across all of Nicaragua and Honduras with the potential slow track after landfall as discussed in the previous paragraph. Heavy rainfall has also been reported in the northern Caribbean Islands of Jamaica...Haiti...eastern Cuba...the Cayman Islands...and eastern Bahamas which is not directly attributed to Eta...but instead as the cold front and upper divergence region of the eastern North America upper trough interact with Eta's moisture...but nonetheless flash flooding is a possiblity here as well. Another round of heavy rainfall in a few days is likely across the Cayman Islands...western and central Cuba...the central and western Bahamas...and Florida peninsula as Eta's remnants become entangled with the forecast strengthening cut-off upper trough...and intersts here should monitor this situation carefully as Eta could regenerate into a tropical cyclone in this interaction...or alternatively a second subtropical/tropical system could emerge to the north of Eta if Eta does not line up with the divergence maximum of the cut-off upper trough.

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

0 Hr Position (1800Z Nov 3)...140 mph maximum sustained wind major hurricane centered just offshore of the northern Nicaragua coast at 13.7N-83.3W

IOH 24 Hr Forecast (1800Z Nov 4)...35 mph maximum sustained wind tropical depression centered over northeastern Nicaragua at 13.7N-84.5W

IOH 48 Hr Forecast (1800Z Nov 5)...Remnant low pressure centered over the Nicaragua/Honduras border at 13.7N-86W

IOH 72 Hr Forecast (1800Z Nov 6)...Remnant low pressure centered over southern Honduras at 14.5N-88W

IOH 96 Hr Forecast (1800Z Nov 7)...Remnant low pressure centered offshore of Honduras at 16.2N-85W

IOH 120 Hr Forecast (1800Z Nov 8)...Remnant low pressure centered over the Cayman Islands at 19.5N-80W


...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 Major Hurricane Eta...weakens to an inland remnant low while crossing the central Nicaragua/Honduras border at 30 hours...remnant low moves northwest toward the east coast of the Yucatan peninsula by 78 hours...while lifting northeastward remnant low regenerates into a large/broad tropical storm centered west of the Cayman Islands at 19N-84.5W...tropical storm makes landfall over western Cuba at 108 hours...tropical storm curves northward toward southern Florida peninsula by 120 hours.


1200Z ECMWF Model Run...For Major Hurricane Eta...weakens to a remnant low over Honduras between 24 and 48 hours...remnant low lifts northeastward from Honduras and into the western Caribbean Sea by 96 hours...accelerates northeastward into western Cuba by 120 hours as a re-strengthening tropical cyclone.


1200Z GFS Model Run...For Major Hurricane Eta...weakens to an inland remnant low while crossing the central Nicaragua/Honduras border at 36 hours...remnant low lifts northward into western Caribbean Sea from Honduras by 66 hours...accelerates northeastward into western Cuba by 96 hours as a re-strengthening tropical cyclone...tropical cyclone bends northward into the southern Florida peninsula by 120 hours.


1200Z NAVGEM Model Run...For Major Hurricane Eta...weakens to an inland remnant low while crossing the central Nicaragua/Honduras border at 24 hours...remnant low lifts northward into western Caribbean Sea from Honduras by 66 hours...redevelops into a tropical storm offshore of Honduras in 84 hours...restrengthens into a hurricane while moving east-northeast across the Cayman Islands in 102 hours...crosses central Cuba as a strong hurricane in 114 hours...curves northward into the western Bahamas as an intense hurricane by 126 hours.

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