MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #176
*******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 10 2020 7:46 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 sections below for a tropical wave of low pressure currently in the eastern Caribbean Sea being monitored for tropical development.
TROPICAL STORM ETA...While steered beneath the west side of the upper vortex in the region...Tropical Storm Eta in the southeastern Gulf of Mexico has swung southwestward in track towards the waters just offshore of the northwestern Cuba coast. In its battle with the upper vortex...Eta has done much better this afternoon by firing a persistent small circular thunderstorm mass covering the center. Even though the upper flow above Eta at 200 mb is cyclonic and non-divergent due to the west side of the overhead upper vortex...Eta has been able to intensify back to 60 mph maximum sustained winds after dipping to a mininum of 50 mph in the last 24 hours. Therefore its probable that Eta's renewed thunderstorm activity has established a warm core outflow layer tucked below the 200 mb layer. As the upper vortex weakens from being cut-off from high latitude cold air and from Eta's thunderstorm latent heat release...Eta should begin to drift northward in track as low-level southerly flow sets up between the deep-layered ridge moving into the western Atlantic and the upper trough and surface cold front that has moved into the central US. Therefore I now anticipate Eta to become a hurricane in 24 hours as it lifts northward away from the suppressing upper vortex...with the forecast position also keeping Eta south of the shearing upper southwesterly winds to set up ahead of the central US upper trough and also another upper trough over central Canada to quickly follow behind. By 48 hours...a northeast drift closer to western Florida peninsula coast is likely as the ridge weakness of the surface cold front tied to the leading upper trough from the central US shifts east...with the track being slow due to the narrowness of ridge weakness associated with the surface front. Some light northwesterly shear should overspread Eta during this time in between the exiting central US upper trough and a Gulf of Mexico upper ridge to build behind the upper trough...so I weaken Eta to back to a strong tropical storm by then. The leading upper trough from the central US and trailing upper trough over central Canada should lift out of the region by 72 hours...closing the surface ridge weakness. The 1200Z cycle of the GFS has trended further south with the positon of the eastern US surface ridge to build in the wake of the upper troughs...thus this ridge has an oppurtunity to nudge Eta eastward closer to the western Florida coast during that time as shown in the forecast below. By 96 and 120 hours...another upper trough to move rapidly from the southwestern to northeastern US should weaken the eastern US surface ridge as the strongest part of the surface ridge passes north of Eta...but the forecast weakening of the ridge won't be enough to turn Eta north. Instead for now I show a slow westward drift commencing under the weakened eastern US surface ridge. A slowly strengthening category 1 hurricane is shown in my forecast below from 72 to 120 hours as a Gulf of Mexico upper ridge with low shear and upper outflow remains in place. The only reason I show slow strengthening at this time is in case the 1200Z GFS and 1200Z NAVGEM are correct in bringing Eta further north in the short term such that it gets negatively sheared on the north side of the Gulf of Mexico upper ridge in the long term...and in case the slow motion of Eta over the next few days upwells cooler waters.
On the whole...my updated forecast is the same as yesterday...with an initial north to northeast drift in the short-term...and then a slow turn to the west in the long term as Eta becomes a steadily intensifying hurricane. However forecast points are shifted to the south and west due to the current position of Eta...with an increase in the forecast intensity due to the current strength of the storm.
Given these forecast updates:
*Eta is currently a compact tropical cyclone and thus the strongest winds remain just offshore of western Cuba. Interests here should have finished preparations by now for tropical storm conditions...and coastal sea swells will remain strong on the northwest coast of Cuba regardless of whether the tropcial storm force winds make it on shore or not. The northerly surface flow on the west side of Eta will also cause coastal sea swells on the north shore of the Yucatan peninsula.
*The Florida Keys will continue to experience sea swells generated by the east side of Eta until the tropical storm moves away from the southeastern Gulf of Mexico. Exactly when that will be is uncertain due to the highly uncertain track forecast amid the currently weak steering currents.
*Although there remains long term uncertainty in Eta’s forecast track...there remains a chance that sometime this week Eta brings tropical storm conditions onto the northwestern or southwestern Florida peninsula coast should the center move close enough to shore. If the intensity forecast below verifies...there is a chance of hurricane force condtions. Interests here should gather storm preparation supplies early to avoid last minute shopping crowds amid the COVID-19 virus outbreak. When in public...wearing a mask and frequent hand sanitizing will protect you from the COVID-19 virus. 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.
*Due to the typical larger forecast error beyond 5 days...it is hard to know at this time if Eta will move into Florida and dissipate from land interaction and wind shear...or track westward across the Gulf of Mexico and later threaten the US Gulf coast west of Florida. Therefore at the present time I have not mentioned the US Gulf coast west of Florida in regards to Eta on the home page bulletins of this site.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1800Z Nov 10)...60 mph maximum sustained wind tropical storm centered just offshore of the northwestern Cuba coast at 22.9N-85.1W
IOH 24 Hr Forecast (1800Z Nov 11)...75 mph maximum sustained wind hurricane centered in the southeastern Gulf of Mexico at 24.5N-85.1W
IOH 48 Hr Forecast (1800Z Nov 12)...65 mph maximum sustained wind tropical storm centered offshore of the southwestern Florida peninsula coast at 26N-84.5W
IOH 72 Hr Forecast (1800Z Nov 13)...75 mph maximum sustained wind hurricane centered just offshore of the southwestern Florida peninsula coast at 26N-83.5W
IOH 96 Hr Forecast (1800Z Nov 14)...80 mph maximum sustained wind hurricane centered offshore of the southwestern Florida peninsula coast at 26N-84W
IOH 120 Hr Forecast (1800Z Nov 14)...85 mph maximum sustained wind hurricane centered in the eastern Gulf of Mexico at 26N-86W
SUBTROPICAL STORM THETA (RECENTLY UPGRADED TO TROPICAL STORM THETA)...The central Atlantic subtropical surface low pressure supported by the eastern divergence zone of the upper trough in the region has made history in the last 24 hours by becoming Subtropical Storm Theta...making the 2020 Atlantic Hurricane season have the highest total number of tropical and subtropical storms (29) on record! The previous record of 28 was set in 2005. As if that was not enough...Theta became stronger than forecast at 70 mph maximum sustained winds and by 4 PM EDT earlier today achieved full tropical status according to the NHC. Considering the 200 mb upper flow is linear and divergent as we typically see on the east side of mid-latitude upper troughs...Theta’s thunderstorm generated warm core (tropical) upper outflow probably exists below the 200 mb layer. Theta’s thunderstorm bands which have primarily been on the northwest side of the circulation center have been weakening on colorized infrared satellite pictures tonight...as the tropical storm has reached waters below 26 deg C and the upper air temps are not cold enough for instability (in the vicinity of Theta...the 200 mb height is forecast to be 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 will cause the supporting upper trough of Theta to tilt southwest-to-northeast with time...and this tilt will also be encouraged as the upper trough tries to link up with the current north Atlantic upper trough...as well as a shortwave upper trough from northeast Canada and current central US upper trough to move rapidly across the far north Atlantic. This tilt will potentially increase the westerly shear over Theta...and combined with increasingly cooler waters I do not see Theta hanging on to tropical characteristics beyond 24 hours as the NHC and models show. However Theta should retain strength even if it loses tropical characteristics as it remains aligned with the eastern divergence zone of the supporting upper trough...but I show Theta weakening back to 60 mph maximum sustained winds as I forecast the boost provided by the thunderstorm warm core outflow to dwindle as Theta loses thunderstorm intensity.
Updated forecast track is nudged eastward in the short-term due to Theta’s current position...but is the same in the long term as the previous track still lines up with the upper divergence maximum of the supporting upper trough in the 1200Z GFS model run. By 96 and 120 hours the upper trough is forecast in the 1200Z GFS 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.
Regardless of whether or not this system 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 Forecast (1800Z Nov 10)...70 mph maximum sustained wind tropical storm centered at 29.4N-36.2W
IOH 24 Hr Forecast (1800Z Nov 11)...60 mph maximum sustained wind tropical storm centered at 30N-32.5W
IOH 48 Hr Forecast (1800Z Nov 12)...60 mph maximum sustained wind frontal cyclone centered at 30N-29W
IOH 72 Hr Forecast (1800Z Nov 13)...60 mph maximum sustained wind frontal cyclone centered at 31N-25W
IOH 96 Hr Forecast (1800Z Nov 14)...Frontal low centered west of the Canary Islands at 31N-20W
IOH 120 Hr Forecast (1800Z 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 67W as it moves across the eastern Caribbean Sea...and is currently generating squalls of thunderstorm to the north and east of the wave axis due to 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 initially steady west motion of the tropical wave across the Caribbean is expected. However by 72 and 96 hours...I gradually slow the west speed of the tropical wave to an eventual stall as a drop in surface pressures to the northeast 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 northeastern lobe of low surface pressure potentially weakening the steering currents on the south side of the deep-layer ridge. The GFS continues to show the upper vortex currently over 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 72 and 96 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 northeast such that a southwest-to-northeast surface trough forms and becomes supported by the eastern divergnece zone of the southwest-to-northeast upper trough shown in the GFS. This shearing upper trough is why I have lowered odds of development to 0% through 96 hours. The thunderstorm activity of the forecast tropical disturbance will likely weaken the shearing upper trough with latent heat release by 120+ 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 above 0%. The upper anticyclone will likely create a more consolidated surface low pressure area that will be able to be steered...but I forecast a slow westward track to commence by 120 hours due to how weak a steering eastern US surface ridge is forecast to be by that time. If Tropical Eta is still in progress in the Gulf of Mexico in the long range...the steering provided by this ridge would be further weakened. My updated forecast track remains near Jamaica by days 3 to 5...therefore I continue to mention Jamaica in relation to this area of interest on the home page bulletins on this site.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1800Z Nov 11)...0% chance of tropical cyclone formation (central Caribbean Sea near 15N-71W)
IOH 48 Hr Outlook (1800Z Nov 12)...0% chance of tropical cyclone formation (central Caribbean Sea near 15N-74W)
IOH 72 Hr Outlook (1800Z Nov 13)...0% chance of tropical cyclone formation (central Caribbean Sea south-southeast of Jamaica near 15N-76W)
IOH 96 Hr Outlook (1800Z Nov 14)...0% chance of tropical cyclone formation (central Caribbean Sea south-southeast of Jamaica near 15N-76W)
IOH 120 Hr Outlook (1800Z Nov 15)...30% chance of tropical cyclone formation (central Caribbean Sea south of Jamaica near 15N-78W)
...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 Storm Eta...drifts northward to 27N-84.5W by 66 hours...turns westward to central Gulf of Mexico while weakening to a remnant low by 120 hours. For Subtropical Storm Theta...reaches Madeira Island at 114 hours....center located just east of the island at 120 hours...in long range turns northeast and weakens offshore of Portugal. For area of interest #1...tropical low pressure forms near 15N-75W at 78 hours...tropical cyclone formation suggested just east of northern Nicaragua at 126 hours....in long range crosses northern Nicaragua while making landfall as a weak tropical cyclone.
0000Z ECMWF Model Run...For Tropical Storm Eta...drifts northward and makes landfall at the Alabama/Mississippi coastal region as a weakening tropical depression just after 96 hours. For Subtropical Storm Theta...reaches Madeira Island by 120 hours...in long range turns northeast and weakens offshore of Portugal. For area of interest #1...tropical low pressure forms near 15N-77.5W at 96 hours...through 168 hours drifts southward offshore of Nicaragua without tropical cyclone formation.
1200Z GFS Model Run...For Tropical Storm Eta...drifts north-northeast and makes landfall on the northwest coast of the Florida peninsula at 66 hours while a tropical depression...in long range weakens to a remnant low while drifting westward back into northeastern Gulf of Mexico. For Subtropical Storm Theta...reaches 33N-24W at 120 hours. For area of interest #1...tropical low pressure forms near 14N-72W at 72 hours...compact tropical cyclone forms at 15N-75W at 108 hours...significant strengthening of compact tropical cyclone by 120 hours while located at 15N-76.5W.
1200Z NAVGEM Model Run...For Tropical Storm Eta...drifts north-northeast and makes landfall on the northwest coast of the Florida peninsula at 72 hours while a tropical depression...shortly thereafter weakens to a remnant low while drifting westward back into northeastern Gulf of Mexico. For Subtropical Storm Theta...reaches 33.5N-24W at 120 hours. For area of interest #1...broad tropical low pressure forms near 15N-76W at 84 hours...tropical depression forms at 16N-80W at 108 hours...tropical storm strength reached by 120 hours while located at 16.5N-82W.