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 #177

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


...WEDNESDAY NOVEMBER 11 2020 12:45 PM EDT...

See Hurricane 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.


HURRICANE ETA...As expected in my previous forecast...Eta's thundestorm bursts in the last 24 hours have caused the tropical storm to re-strengthen into a category 1 hurricane in the southeastern Gulf of Mexico. Although the thunderstorms in Eta's circulation have largely dissipated this morning...aircraft reconaissance has measured Eta at minimal hurricane strength. It is probable that Eta reached hurricane strength early this morning before the thunderstorms diminished and before aircraft reconaissance reaached Eta. What was not well-predicted was an unexpected north-northeast acceleration toward the western Florida peninsula coast. A look at the upper-level wind field shows the cold core upper vortex that has been over Eta has weakened to an upper trough axis located just west of Eta's surface center due to Eta's earlier thunderstorm latent heat release and also as the vortex has been cut-off from high-latitude cold air. It is possible Eta's early north-northeast acceleration was kicked off by the southwesterly flow on the east side of this upper trough. This now positions Eta to continue north-northeast into the narrow surface ridge weakness tied to the cold front being driven by the central US upper trough instead of missing the weakness...and a landfall on the west Florida peninsula coast now appears imminent.


The intensity forecast is tricky...it could very well be in the next 24 hours that Eta weakens well below hurricane force due to increasing land interaction with the Florida peninsula... water temps near the Florida coast that are below 26 deg C...and westerly shear to be induced by the leading upper trough ejecting from the central US and another fast-moving north-central US and south-central Canada upper trough to follow behind. It could also be that Eta maintains strength by redeveloping another round of thunderstorm flares aided by the divergent nature of the upper westerly flow or the upper divergence on the east side of the upper trough in the southeastern Gulf of Mexico. Therefore my intensity forecast in the next 24 hours lies between these two scenarios and has Eta making landfall on the northwest Florida peninsula coast as a strong tropical storm. By 48 hours...as the leading upper trough from the central US and trailing upper trough over the northern US and southern Canada quickly exit the region...an upper ridge is forecast to build over the Gulf of Mexico...but Eta will remain under northwesterly shear on the northeast side of the upper ridge such that I forecast Eta to weaken to a remnant low due to the combination of land interaction while moving across north Florida and the shear. The remnant low is likely to bend eastward in track and emerge from northeastern Florida and into the western Atlantic as Eta follows the surface ridge weakness tied to the cold front approaching from the central US. The forecast track point below at 72 hours calls out Eta remaining a remnant low...but I continue to forecast Eta through that time as there maybe a chance Eta regenerates into a tropical depression as wind shear potentially relaxes when the building upper ridge from the Gulf of Mexico expands over Eta and as the circulation would be near the warm 26 deg C Gulf stream waters. By 96 hours another upper trough to move rapidly from the southwestern to northeastern US should increase the upper westerly shearing flow over Eta and finally bring and end to this long-lasting tropical system.


Given these forecast updates:


*Now that Eta is finally lifting north-northeastward away from the southeastern Gulf of Mexico...the Florida Keys...north coast of the Yucatan peninsula...and the northwestern Cuba coast will see a drop in coastal sea swells later today.


*Interests across the western Florida peninsula should rush preparations for tropical storm conditions...with possible hurricane conditions...to completion as weather conditions are already deteriorating. 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...as a public storm shelter may not be as ideal in controlling your exposure to the COVID-19 virus.

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

0 Hr Position (1200Z Nov 11)...75 mph maximum sustained wind hurricane centered in the southeastern Gulf of Mexico at 26.2N-83.7W

IOH 24 Hr Forecast (1200Z Nov 12)...60 mph maximum sustained wind tropical storm centered on the northwestern Florida peninsula coast at 28N-82.5W

IOH 48 Hr Forecast (1200Z Nov 13)...Remnant low pressure centered just offshore of northeastern Florida at 30N-80.5W

IOH 72 Hr Forecast (1200Z Nov 14)...Remnant low pressure centered in the western Atlantic at 30.5N-76W

IOH 96 Hr Forecast (1800Z Nov 14)...Dissipating remnant low pressure in the western Atlantic at 30.5N-74W


TROPICAL STORM THETA...Theta continues to be a shallow warm core tropical cyclone whose surface inflow and anticyclonic outflow remain tucked below upper-level southwesterly flow on the east side of the central Atlantic upper trough. The tropical storm is over waters below 26 deg C and its eastward track that remains in tandem with the supportive upper divergence maximum of the eastward moving central Atlantic upper trough is taking the tropical storm over increasingly cooler waters with time. The upper air temps are also not cold enough for instability (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). The strength of the deep-layered ridge to the west is causing the central Atlantic upper trough just west of Theta to tilt southwest-to-northeast with time...and this tilt will also be encouraged as the central Atlantic upper trough tries to link up with the current northeast and northwestern Atlantic upper troughs...and eventually the current central US upper trough once it also moves rapidly across the far north Atlantic. This tilt is increasing the westerly shear potential over Theta. Theta seemed to be following this increasingly bleak picture by showing weakening thunderstorms through the morning hours and now weakening to 60 mph maximum sustained winds. However recently Theta has fired renewed thunderstorm bursts on the northwest side of the center...probably boosted by the upper divergence on the east side of the central Atlantic upper trough considering that Theta is in an less favorable thermodynamic setting (water temps below 26 deg C and not so cold upper air temps as explained earlier). Thus I have extended the amount of time of Theta's tropical status for another 24 hours...and then forecast Theta to transition to a non-tropical frontal cyclone supported by the central Atlantic upper trough thereafter considering the thermodynamic setting will become less favorable for tropical characteristics with time as Theta moves over progressively cooler water. However I maintain a forecast on Theta for some time in case the NHC and models are correct in Theta holding on to tropical status for longer (this is something I have been doing in earlier posts but did not explain...so I am noting this forecast strategy in this update).


Updated forecast track is unchanged as Theta is on par with the previous track...and as the forecast remains aligned with the upper divergence maximum of the supporting central Atlantic upper trough in the 0600Z GFS model run. By 72 and 96 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 96 hours as I am more confident in Theta weakening by then. After 96 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 central US upper trough and another upper trough to quickly follow behind it over southern Canada.


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 (1200Z Nov 11)...60 mph maximum sustained wind tropical storm centered at 29.8N-33.3W

IOH 24 Hr Forecast (1200Z Nov 12)...60 mph maximum sustained wind tropical storm centered at 30N-30W

IOH 48 Hr Forecast (1200Z Nov 13)...60 mph maximum sustained wind frontal cyclone centered at 30.5N-26W

IOH 72 Hr Forecast (1200Z Nov 14)...Frontal low centered west of the Canary Islands at 31N-21W

IOH 96 Hr Forecast (1200Z Nov 15)...Frontal low centered west of the Canary Islands at 31N-20W


AREA OF INTEREST #1...A surface tropical wave of low pressure is now crossing 70W as it moves into the central Caribbean Sea. However the strongest thunderstorm activity is to the east of the wave axis and supported by an area of upper divergence between the east side of the Caribbean upper ridge cell and west side of the central Atlantic upper trough tied to Tropical Storm Theta. With the deep-layered ridge over the western Atlantic...an initial west motion of the tropical wave is expected. However by 48 to 72 hours...the west speed of the tropical wave is likely to stall as a drop in surface pressures to the northeast or east is likely from an upper divergence maximum to occur between the southwest side of a cut-off upper vortex to originate from the central Atlantic upper trough and east side of the Caribbean upper ridge cell...with this eastern lobe of low surface pressure weakening the steering currents on the south side of the deep-layer ridge. The GFS continues to show the southeastern Gulf of Mexico upper trough currently near Hurricane Eta linking up with the aforementioned upper vortex to originate from the central Atlantic upper trough...essentially creating a southwest-to-northeast upper trough axis that could potentially induce wind shear across this disturbance towards 48 and 72 hours. It is possible we end up with a complex disturbance where the tropical wave stalls in the central Caribbean Sea...and merges with the forecast lobe of surface low pressure to the east such that an east-to-west surface trough forms and becomes supported by the eastern divergnece zone of the southwest-to-northeast upper trough. This shearing upper trough is why I keep odds of development at 0% through 72 hours. The thunderstorm activity of the forecast tropical disturbance will likely weaken the shearing upper trough with latent heat release by 96+ hours as the GFS shows...with a warm core upper anticyclone to form in between the halves of the fracturing and weakening upper trough. This is when I begin to sharply raise odds of development to a peak of 60% by day 5 (the high odds are also due to agreement with eventual tropical cycloe formation in the GFS..ECWMF..and NAVEGEM). The concentrated outflow of the upper anticyclone will likely create a more consolidated surface low pressure area that will be able to be steered by 96+ hours...but I forecast a slow westward track to commence by then due to how weak a steering eastern US surface ridge is forecast to be by that time. Around 120 hours...the current upper vorticity offshore of southwestern 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 currently too far north to influence the steering...therefore it is likely in the longer term that this disturbance'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 the disturbance approaches eastern Nicaragua and eastern Honduras. This is eerily means we could be in for a repeat of tropical cyclone impacts in Nicaragua and Honduras after Hurricane Eta just recently devastated this region with powerful winds and catastrophic rainfall flooding...and unfortunately interests here need to be aware of this disturbance. I also retain statements for Jamaica in regards to this disturbance on the home page bulletins of this site as the forecast track also passes close to the island in 2 to 4 days.

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

IOH 24 Hr Outlook (1200Z Nov 12)...0% chance of tropical cyclone formation (central Caribbean Sea near 15N-73W)

IOH 48 Hr Outlook (1200Z Nov 13)...0% chance of tropical cyclone formation (central Caribbean Sea south-southeast of Jamaica near 15N-75.5W)

IOH 72 Hr Outlook (1200Z Nov 14)...0% chance of tropical cyclone formation (central Caribbean Sea south-southeast of Jamaica near 15N-76W)

IOH 96 Hr Outlook (1200Z Nov 15)...30% chance of tropical cyclone formation (central Caribbean Sea south of Jamaica near 15N-77.5W)

IOH 120 Hr Outlook (1200Z Nov 16)...60% chance of tropical cyclone formation (central Caribbean Sea near 15N-80W)


...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 Hurricane Eta...weakens to a tropical depression while stalling just offshore of the northwestern Florida coast through 66 hours...drifts westward in the northeastern Gulf of Mexico while weakening to a dissipating remnant low...remnant low dissipates at 114 hours. For Tropical Storm Theta...reaches waters just west of Madeira Island at 114 hours...in long range turns northeast and weakens in far northeastern Atlantic. For area of interest #1...broad tropical low pressure forms near 15N-79W at 78 hours...tropical low makes landfall on the Nicaragua/Honduras border at 120 hours without tropical cyclone formation.


0000Z ECMWF Model Run...For Hurricane Eta...makes landfall at hurricane strength on northwest Florida coast between 24 and 48 hours...moves into the Atlantic from the Florida/Georgia border as a tropical depression between 48 and 72 hours...while located near 35N-70W at 120 hours begins to become absorbed by strong frontal cyclone over eastern North America. For Tropical Storm Theta...stalls just west of the Canary Islands from 96 to 120 hours while weakening. For area of interest #1...broad tropical low pressure forms near 15N-75W at 48 hours...tropical cyclone formation suggested near 15N-81W at 120 hours...makes landfall over eastern Honduras as a strengthening compact tropical cyclone at 144 hours.


0600Z GFS Model Run...For Hurricane Eta...makes landfall at hurricane strength on northwest Florida coast at 30 hours...moves into the Atlantic from the Florida/Georgia border as a tropical depression at 42 hours...weakens to a remnant low at 31N-76W at 72 hours...remnant low dissipates at 31N-75W at 102 hours. For Tropical Storm Theta...stalls at 31N-23W from 78 to 102 hours while slowly weakening...additional weakening occurs while accelerating northeastward to 35N-21.5W by 126 hours. For area of interest #1...tropical low pressure forms near 13N-74W at 78 hours...tropical cyclone formation suggested at 15N-77W at 102 hours...strengthens rapidly into a compact hurricane at 15N-80W at 120 hours...in long range landfall as an intense and compact hurricane near Nicarauga/Honduras border suggested.


0600Z NAVGEM Model Run...For Hurricane Eta...makes landfall on the eastern Florida panhandle coast at 36 hours while weakening to a tropical depression...weakens to a remnant low while located inland over the Florida/Georgia border at 48 hours...remnant low dissipates over the coast of South Carolina at 60 hours. For Tropical Storm Theta...passes just north of Madeira Island at 102 hours...in long range weakens while passing offshore of Portugal. For area of interest #1...tropical low pressure forms near 15.5N-74W at 60 hours...passes just south of Jamiaca at 84 hours while developing into a tropical depression...reaches tropical storm strength while passing 17.5N-81W at 102 hours...reaches hurricane strength at 18N-85W at 120 hours.

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