MY 2020 ATLANTIC HURRICANE SEASON BIRDSEYE VIEW POST #175
*******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.**********
...MONDAY NOVEMBER 9 2020 12:30 PM EDT...
See Tropical Storm Eta section below for the only active tropical cyclone in the Atlantic basin. See area of interest sections below for multiple areas being monitored for tropical development.
TROPICAL STORM ETA...A deep-layered ridge remains over the eastern United States...to the north of Tropical Storm Eta and the cut-off upper vortex the tropical storm is interacting with. The surface layer of the ridge is supported by the western convergence zone of the current northwest Atlantic upper trough. The upper layer of the ridge is supported by warm air advection ahead of a strong surface frontal system/upper trough over the western US. This deep-layered ridge is caused what was once a cut-off upper trough over the southeastern Unitd States and Gulf of Mexico to amplify into an upper vortex that is now located just south of Eta's surface center. The north side of the vortex has swung Eta westward across south Florida and the Florida Keys. While exiting the south Florida region this morning...Eta initially was trying to put up a fight against the upper vortex by developing a tight core of thunderstorms...but this activity has since fizzled into weaker broken bands around the center of Eta as the tropical storm has been negatively influenced by dry air from the nearby western convergence zone of the upper vortex. Meanwhile the eastern divergence zone of the upper vortex has produced a lobe of low surface pressure to the southeast...and so with Eta not being able to put up enough thunderstorm latent heat release to weaken the vortex we can expect the upper vortex and lobe of low surface pressure to toss Eta southwestward towards the northwest coast of Cuba. My short-term track forecast is adjusted southward closer to the northwest Cuban coast. Eta has been slowly weakening in the dry air environment...and I anticipate this to continue for the next 24 hours as Eta will remain on the west side of the upper vortex where there is a lack of upper divergence to help Eta.
After 24 hours...the current western US frontal system/upper trough will have reached the central US and have weakened the eastern US deep-layered ridge. In response to the ridge weakening...a northward turn away from the upper vortex and its dry air is anticipated during that time...thus I forecast some re-strengthening by 48 hours as the southward-adjusted forecast track will keep Eta south of the shearing upper southwesterly flow ahead of the central US upper trough...and also another upper trough over central Canada to quickly follow behind. By 72 hours...a northeast drift closer to western Florida peninsula coast is likely due to the upper southwesterly flow and surface cold front tied to the leading upper trough from the central US...with the track being slow due to the narrowness of ridge weakness associated with the surface front. The upper southwesterly flow would likely be shearing Eta during this time...thus I drop forecast intensity again at 72 hours. The southward-adjusted track forecast has bigger consequences at 96+ hours...as the leading upper trough from the central US and trailing upper trough over central Canada lift out of the region...closing the surface ridge weakness such that Eta misses the opportunity to accelerate northeast into the surface ridge weakness. Thus for now I begin to turn Eta westward toward the central Gulf of Mexico by 96 to 120 hours under the influence of a surface ridge forecast to rebuild over the eastern United States in the wake of the exiting upper troughs. I also forecast Eta to gain hurricane strength by 120 hours as the southwesterly upper shearing winds relax once the upper troughs leave the region...and as my updated forecast track now keeps Eta south of the 26 deg C water temp isotherm.
Given these forecast updates:
*Eta has already crossed central Cuba...but western Cuba may see some tropical storm conditions tomorrow if Eta tracks far south enough. Interests here should use today to finish preparing for such conditions. The northerly surface flow on the west side of Eta will also cause coastal sea swells on the north shore of the Yucatan peninsula.
*Weather conditions have improved across the western Bahamas...south Florida...and the eastern Florida Keys as Eta pulls away. The western Florida Keys will experience gusty winds with some damage potential for a few more hours. The Keys will continue to experience sea swells generated by the east side of Eta for a couple of days as Eta tracks erratically near the northwestern Cuba coast.
*Although there is some long term uncertainty in Eta’s forecast track...there remains a chance that sometime this week Eta crosses northern Florida as a tropical storm or at least bring such conditions onshore should it track slowly just offshore of the northwest Florida peninsula coast. 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 northern Florida and dissipate from land interaction and wind shear...or track westward across the northern Gulf of Mexico and later threaten the US Gulf coast beyond northern Florida as the track forecast below currently suggests. Therefore 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 (1200Z Nov 9)...60 mph maximum sustained wind tropical storm centered just west of the Florida Keys at 24.6N-83.4W
IOH 24 Hr Forecast (1200Z Nov 10)...50 mph maximum sustained wind tropical storm centered just offshore of the northwestern Cuba coast at 23.5N-84.5W
IOH 48 Hr Forecast (1200Z Nov 11)...60 mph maximum sustained wind tropical storm centered in the eastern Gulf of Mexico at 25N-84.5W
IOH 72 Hr Forecast (1200Z Nov 12)...50 mph maximum sustained wind tropical storm centered offshore of the western Florida peninsula coast at 27N-84W
IOH 96 Hr Forecast (1200Z Nov 13)...60 mph maximum sustained wind tropical storm centered offshore of the western Florida peninsula coast at 27N-84W
IOH 120 Hr Forecast (1200Z Nov 14)...75 mph maximum sustained wind hurricane centered over the central Gulf of Mexico at 27N-87.5W
AREA OF INTEREST #1...The central Atlantic surface low pressure is arguably the most impressive feature on satellite pictures in the Atlantic basin today...featuring a rather large comma shaped thunderstorm mass with a thunderstorm burst located just northwest of the center as its supporting upper trough has continued to amplify in response to the amplifying deep-layered ridge over the eastern United States and western Atlantic. As each day passes...computer models have shown the upper trough moreso amplifying...which will reduce the shear over the surface low while also producing an upper divergence maximum for a consolidated surface circulation to strengthen. Based on the latest satellite pictures and model runs which show a circular consoldiated circulation gaining high strength...I have begun a subtropical cyclone formation forecast as outlined below. I expect a very high chance that this system will be upgraded to a subtropical storm later today.
The current tropical characteristics of the surface low (thunderstorm strong enough to produce warm core upper outflow) are being allowed as the circulation is centered over water temperatures of 26 deg C. Forecast track below is based on following the the upper divergence maximum of the upper trough in the 0600Z GFS model run as the upper trough shifts east...which will take this circulation to water temps below 26 deg C after 48 hours (24 deg C by 72 and 96 hours...and 23 deg C by 120 hours). The upper trough is not forecast to be cold enough to help drive instability...in the vicinity of this system 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. So it is curious that the models seem to suggest this system retaining a tropical-like circular structure in the surface pressure field all the way through 120 hours. Even the 0600Z GFS at 72 hours briefly suggests that this system could briefly become fully tropical by showing a small area of anticyclonic warm core outflow popping up in the midst of the cold upper trough. However with the possiblity of the upper trough of this system merging with the current northwest Atlantic upper trough in the long range...with the merger taking a southwest-northeast tilt that would increase the southwesterly shear over this system which would make it harder to keep thunderstorms stacked over the center...and with the long-term less favorable thermodynamic picture (cooler water temps and not cold enough upper-level temps) described above...and also with the possiblility of the current north Atlantic frontal cyclone's cold front overruning this circulation...I do not see the case for keeping this system tropical after 48 hours...instead I forecast it to become a frontal cyclone that remains supported by the eastern divergence zone of the upper trough.
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 continue eastward.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Nov 9)...Surface low pressure centered at 28N-43W
IOH 24 Hr Forecast (1200Z Nov 10)...60 mph maximum sustained wind subtropical storm centered at 28N-40W
IOH 48 Hr Forecast (1200Z Nov 11)...60 mph maximum sustained wind subtropical storm centered at 30N-35W
IOH 72 Hr Forecast (1200Z Nov 12)...60 mph maximum sustained wind frontal cyclone centered at 31N-30W
IOH 96 Hr Forecast (1200Z Nov 13)...60 mph maximum sustained wind frontal cyclone centered at 31N-25W
IOH 120 Hr Forecast (1200Z Nov 14)...60 mph maximum sustained wind frontal cyclone centered west of the Canary Islands at 31N-20W
AREA OF INTEREST #2...A tropical wave of low pressure is now crossing 62.5W as it moves across the eastern Caribbean Sea. There is potential for this wave to experience low shear and upper outflow as it moves beneath the Caribbean upper ridge cell forecast to persist between the upper vortex forming currently over Tropical Storm Eta and central Atlantic upper trough associated with area of interest #1. With the deep-layered ridge over the eastern United States to shift into the western Atlantic...an initially steady west motion of the tropical wave across the Caribbean is expected. However later in the forecast period...I gradually slow the west speed of the tropical wave to an eventual stall by 120 hours...as mutiple models suggest a drop in surface pressures further to the northeast by then 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. This is most exemplified in the 0600Z runs of the GFS and NAVGEM from this morning which shows the tropical wave essentially stalling in the central Caribbean Sea while undergoing a fujiwhara interaction with a developing surface low pressure lobe to the northeast. The GFS also shows 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 120 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-norhtheast upper trough shown in the GFS. The potential for this shearing upper trough to form could be why the GFS and NAVGEM have recently dropped showing development...which is why my peak odds of development by day 5 (set at 35%) are lower than the NHC's latest outlook of 50%. Depsite the less favorable long range upper wind outlook from the GFS... the odds of development are not 0% as the CMC remains aggressive in showing development perhaps as it does not forecast a shearing upper trough to consolidate across the Caribbean just like the aggressive GFS and NAVGEM runs of yesterday. Even in the less favorable scenario posed by the GFS today...the thunderstorm activity of this forecast tropical disturbance could weaken the shearing upper trough with latent heat release beyond 5 days. My updated forecast track remains near Jamaica by day 5...therefore I continue to mention Jamaica in relation to this wave on the home page bulletins on this site.
******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (1200Z Nov 10)...0% chance of tropical cyclone formation (eastern Caribbean Sea near 15N-67.5W)
IOH 48 Hr Outlook (1200Z Nov 11)...10% chance of tropical cyclone formation (central Caribbean Sea near 15N-71W)
IOH 72 Hr Outlook (1200Z Nov 12)...20% chance of tropical cyclone formation (central Caribbean Sea near 15N-74W)
IOH 96 Hr Outlook (1200Z Nov 13)...30% chance of tropical cyclone formation (central Caribbean Sea south-southeast of Jamaica near 15N-76W)
IOH 120 Hr Outlook (1200Z Nov 14)...35% chance of tropical cyclone formation (central Caribbean Sea south-southeast of Jamaica near 15N-76W)
...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...curves southwest to the west tip of Cuba by 24 hours...drifts northward toward waters offshore of the northwest Florida peninsula coast by 96 hours...drifts southwestward to 26N-86W by 120 hours while weakening to a tropical depression. For area of interest #1...intensifies as a consolidated circulation through 48 hours while reaching 29N-36W...reaches 33.5N-21.5W by 120 hours. For area of interest #2...tropical wave currently crossing the Lesser Antilles organizes into a tropical low pressure near 15N-72.5W at 78 hours...tropical cyclone formation suggested at 12.5N-79W at 132 hours...significant strengthening suggested in long range.
0000Z ECMWF Model Run...For Tropical Storm Eta...curves southwest to the west tip of Cuba by 24 hours...curves northward and makes landfall on the northwest coast of the Florida peninsula at 96 hours...weakens to a remnant trough while reaching the northeast coast of Florida at 120 hours. For area of interest #1...intensifies as a consolidated circulation through 48 hours while reaching 30N-35W....reaches 33.5N-20.5W by 120 hours. For area of interest #2...no tropical cyclone formation shown.
0600Z GFS Model Run...For Tropical Storm Eta...curves southwest to the west tip of Cuba by 24 hours...through 36 hours intensifies into a hurricane while nearly stationary on northwestern Cuba coast...drifts slowly northeast 26N-84.5W by 90 hours as a strong hurricane...while drifting westward to 24.5N-89W by 120 hours weakens to a tropical storm. For area of interest #1...intensifies as a consolidated circulation through 48 hours while reaching 29N-35W....reaches 31.5N-23W by 120 hours. For area of interest #2...tropical wave currently crossing the Lesser Antilles organizes into a tropical low pressure near 15N-72.5W at 78 hours...no tropical cyclone formation suggested in long range as a second surface low forms north of the Caribbean Islands that heads west to the Bahamas...with the low from 15N-72.5W becoming generally stationary in the central Caribbean due to a fujiwhara interaction with low north of the Caribbean islands.
0600Z NAVGEM Model Run...For Tropical Storm Eta..whirls southwest to waters just offshore of western Cuba by 30 hours...reaches waters offshore of the northwest Florida peninsula by 108 hours...drifts slowly west-northwest across the northeastern Gulf of Mexico by 120 hours. For area of interest #1...intensifies as a consolidated circulation through 48 hours while reaching 29N-34W...reaches hurricane strength east-southeast of the Azores at 120 hours while located at 35N-21.5W. For area of interest #2...tropical wave currently crossing the Lesser Antilles organizes into a tropical low pressure just southeast of Jamaica at 90 hours...drifts south to 13N-72.5W by 126 hours while undergoing a fujiwhara interaction with another broad low pressure that forms north of the Caribbean Islands (no tropical cyclone formation shown in long range).