*******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 24 2020 11:30 PM EDT...
Satellite Image as of 0400Z (red indicates an active tropical cyclone of remnants of a tropical cyclone...green indicates an area of interest currently in the NHC outlook...yellow indicates an area of interest currently in the NHC outlook):
NHC TAFB Surface Analysis 0000Z:
GFS Model Upper Level Winds 0000Z:
See area of interest section below for an update on the surface low pressure southeast of Bermuda being monitored for subtropical cyclone formation. Elsewhere...computer models agree that the north end of the western Atlantic upper trough currently interacting with the area of interest will become a cut-off upper vortex in the northeast Atlantic between the Canary Islands and Portugal in 4 to 5 days thanks to a deep-layered ridge currently developing west of the upper trough. This cut-off upper vortex will trigger a potentially strong surface cyclone in the region...and even though water temps are currently running at 18 to 20 deg C...the upper vortex is forecast to be rather cold that it may aid in the generation of thunderstorms with the surface cyclone such that acquisition of tropical characteristics may have to be watched for. Therefore may consider adding another area of interest in the northeast Atlantic in the coming days. Regardless...the surface cyclone may produce gusty winds to the Canary Islands if it forms further to the south.
AREA OF INTEREST #1...The surface low pressure that formed in the western Atlantic yesterday has merged with a cold front driven by a large scale incoming upper trough...and is being pushed by the cold front into the central Atlantic while passing southeast of Bermuda. The surface low pressure is currently located at 26.5N-62.5W...and the updated forecast track in the outlook below is adjusted southward accordingly due to this current position and latest model consensus that had also trended notably more southward. The south end of the cold front containing the surface low pressure of interest is expected to evolve into a subtropical disturbance by 24+ hours as the base of the front’s upper trough becomes cut-off into a vortex in response to an amplifying upstream deep-layered ridge to the northwest. Models agree that the surface low pressure of interest will transition into a subtropical low pressure supported by the eastern divergence zone of the forecast upper vortex. I have raised odds of subtropical cyclone formation to 40% as the latest model consensus and updated forecast track below are over warm 26 deg C water...even though the surface low pressure is shown to be weaker in today’s model runs. After 24 hours the surface low is forecast to reverse to a west-southwest track under the influence of the deep-layered ridge to the northwest...with the track stalling from 72 to 96 hours due to a blocking surface ridge to the west to be supported by an approaching shortwave upper trough crossing the northwest Atlantic. The 1800Z GFS suggests that during this time the supportive divergence zone of the shortwave upper trough may overspread the surface low...thus I have extended the peak 40% odds of subtropical cyclone formation through 0000Z November 29. The frontal low pressure associated with this shortwave upper trough will likely drag the surface low northeastward by 120 hours...and this is when I drastically lower odds of subtropical cyclone formation while the surface low will likely exposed to the back west side of the shortwave upper trough where northwesterly shear and upper convergence would be present.
*******Infohurricanes.com outlook. Visit hurricanes.gov (hurricanes dot gov) for official outlook***********
IOH 24 Hr Outlook (0000Z Nov 26)...0% chance of subtropical cyclone formation (central Atlantic near 26.5N-55W)
IOH 48 Hr Outlook (0000Z Nov 27)...40% chance of subtropical cyclone formation (central Atlantic near 25.5N-57W)
IOH 72 Hr Outlook (0000Z Nov 28)...40% chance of subtropical cyclone formation (central Atlantic near 25N-59W)
IOH 96 Hr Outlook (0000Z Nov 29)...40% chance of subtropical cyclone formation (central Atlantic near 25N-59W)
IOH 120 Hr Outlook (0000Z Nov 30)...10% chance of subtropical cyclone formation (central Atlantic near 27.5N-55W)
...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 area of interest #1...surface low separates from front by 48 hours and reaches 25N-58.5W by 78 hours...afterwards drifts northward toward northwest Atlantic frontal low and weakens to a surface trough near 31N-57.5W by 108 hours.
1200Z ECMWF Model Run...For area of interest #1...surface low separates from front by 48 hours and reaches 25.5N-59.5W by 72 hours...afterwards drifts northward toward northwest Atlantic frontal low and weakens to a surface trough near 30N-55W by 120 hours.
1800Z GFS Model Run... For area of interest #1...surface low separates from front by 48 hours while weakening to a surface trough...surface trough does not redevelop into a surface low.
1800Z NAVGEM Model Run...For area of interest #1...surface low separates from front by 24 hours while located at 26.5N-59.5W...surface low dissipates near 24N-64W just after 90 hours.