MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #172
*******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.**********
...FRIDAY NOVEMBER 6 2020 11:28 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. The broad surface spin has developd two tighter centers of rotation...one to the south and the other to the north. Although the southern center has better organized shower and thunderstorm activity when compared to the northern center...colorized infrared satellite imagery shows this activity is not strong enough to declare a subtropical cyclone. Upper air support is also quickly shifting to the less organized northern center as a north Atlantic surface cold front approaches from the northwest...with the eastern divergence zone of the front's upper trough expected to support the northern center such that the southern center will lose its identity within the northern center. The arrival of the upper trough and cold front will also make the northern center less tropical and pull it further north into even cooler waters. Therefore subtropical cyclone formation is not expected in the region.
TROPICAL DEPRESSION ETA...The National Hurricane Center (NHC) continues to issue advisories on Eta as a tropical depression even though it appears the surface circulation is diffuse without a tight center as we traditionally see in a tropical cyclone. The low pressure field of Eta is depicted as a bean shaped area covering the western Caribbean...Central America...and the far eastern Pacific instead of a traditional circular shape in the 1200Z surface analysis as shown in the above charts. ASCAT satellite passes of surface winds are not conclusive in showing a well-defined tight rotation while missing the area the NHC declares as the current center offshore of Belize. Satellite animation also does not show a well-defined spin either at the moment. However to avoid confusion and to allow tropical storm warnings and watches to go up for Cuba and the Cayman Islands...I believe the NHC is keeping Eta as a tropical depression instead of a remnant low as it is likely to soon regenerate into a tropical storm supported by the eastern divergence zone of the cut-off upper trough to the north while moving into those areas under the guidance of the upper trough. Forecast track below is the same as my previous but with a northward adjustment given where the NHC is currently positioning the center of Eta. I did not do any west-to-east adjustment of my track forecast points as the NHC position is only just west of my previous foreacst. I believe the GFS and NAVGEM overdo the intensification of Eta as the large size of the supporting upper-level divergence field of the cut-off upper trough 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 over the next couple of days should continue to have a large comma shaped thunderstorm mass lopsided to the northeast half of its circulation 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 (72+ 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 eastern 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 72 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 northward angle in track through 96 and 120 hours as the models have trended in showing the vigorous frontal system/upper trough over the central United States moreso weakening the eastern United States deep-layered ridge. The upper vortex is bound to weaken due to Eta's thunderstorm latent heat release and while it remains cut-off from cold air while to the south of the deep-laered ridge...but the 0600Z GFS has trended with showing the upper vortex staying a bit stronger...so it is curious that it also shows Eta becoming a hurricane which is something I disagree with at this time as the upper vortex would suppress Eta from developing symmetric warm core upper outflow needed for brisk strengthening...especially since the upper vortex is forecast to be warm (measuring 1236 dekameters in height at 200 mb) such that it would do little in adding to instability and thunderstorm generation. Land interaction with the southern Florida peninsla by 96 hours also prevents me in showing hurricane strength. And finally because the central US upper trough is currently forecast to moreso weaken the eastern United States deep-layered ridge...the upper trough may reverse the upper flow in the eastern Gulf of Mexico a westerly shearing direction by 120 hours such that I do not show strengthening into a hurricane by then either. But for now I also refrain from showing weakening in case the upper-level wind forecasts change again.
Northern Belize and the southern Quintana Roo province of Mexico may see additional heavy rainfall with some flash flooding risk over the next hours from the western fringe of thunderstorm bursts ongoing in Eta's circulation. Interests in the Cayman Islands...Cuba...and the western Bahamas should be 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 6)...35 mph maximum sustained wind tropical depression centered offshore of Belize at 17.8N-87W
IOH 24 Hr Forecast (1200Z Nov 7)...45 mph maximum sustained wind tropical storm centered just west-northwest of Grand Cayman Island at 19.5N-82.5W
IOH 48 Hr Forecast (1200Z Nov 8)...50 mph maximum sustained wind tropical storm centered over the north-central Cuba coast at 23N-79W
IOH 72 Hr Forecast (1200Z Nov 9)...60 mph maximum sustained wind tropical storm centered just west of Andros Island of the western Bahamas at 25N-79W
IOH 96 Hr Forecast (1200Z Nov 10)...60 mph maximum sustained wind tropical storm centered over the southern Florida peninsula at 26N-81W
IOH 120 Hr Forecast (1200Z Nov 11)...60 mph maximum sustained wind tropical storm centered offshore of the west Florida peninsula coast at 27.5N-84W
...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...re-strengthens into a tropical storm and passes between the Cayman Islands and Cuba by 48 hours...crosses western Cuba by 60 hours...turns northwest into the Florida Keys by 72 hours...by 120 hours located in the central Gulf of Mexico at 24.5N-89W as a tropical storm. Elsewhere...tropical wave currently at 50W longitude organizes into a broad tropical low pressure in south-central Caribbean Sea at 150 hours...possible tropical cyclone formation suggested in longer range.
0000Z ECMWF Model Run...For Tropical Depression Eta...re-strengthens into a tropical storm and passes over the Cayman Islands at 48 hours...crosses central Cuba by just before 60 hours...rapidly intensifies into a strong tropical storm just offshore of the north-central Cuban coast at 72 hours...turns west-northwest and passes just southwest of the Florida Keys before 96 hours as a strong tropical storm...reaches hurricane strength in the southeastern Gulf of Mexico at 23N-87.5W at 120 hours.
0600Z GFS Model Run...For Tropical Depression Eta...quickly re-strengthens into a strong tropical storm just southwest of Grand Cayman Island at 24 hours...passes over the Cayman Islands as a strong tropical storm through 42 hours...crosses central Cuba by 48 hours...swings northward into the western Bahamas while becoming a hurricane by 60 hours...curves westward into south tip of the Florida peninsula and the Florida Keys as a hurricane at 84 hours...drifts northwestward offshore of the southwest Florida peninsula coast through 120 hours while remaining at hurricane strength.
0600Z NAVGEM Model Run...For Tropical Depression Eta...quickly re-strengthens into a hurricane just northwest of Grand Cayman Island at 36 hours...passes over western Cuba by 48 hours...curves northward into the south tip of Florida and the eastern Florida Keys by 66 hours...moves northwest along the southwest Florida peninsula coast through 72 hours...reaches northeastern Gulf of Mexico by 120 hours while still at hurricane strength and begins to curve northeastward in track toward the northern Florida peninsula.