*******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.**********
...THURSDAY NOVEMBER 21 2019 3:07 PM EDT...
See Tropical Storm Sebastien section below for additional details for the only active tropical cyclone in the Atlantic basin.
TROPICAL STORM SEBASTIEN...As soon as Sebastien turned northward and north-northeastward in the last 24 hours ahead of an approaching frontal zone from the west...bursts of thunderstorms biased to the east of the center began to better cover the center and also became better organized...and Tropical Storm Sebastien has strengthened further to 60 mph maximum sustained winds. This appears to be from the latest track being more aligned with the upper southwesterly winds generated ahead of the approaching front's upper trough...thus reducing (albeit not eliminating) the wind shear...and also due to the upper divergence zone on the east side of the upper trough arriving and aiding Sebastien. I think Sebastien will strengthen further to 70 mph maximum sustained winds in the next 24 hours...but I am on the fence on forecasting it to become a hurricane as the west side of the circulation still lacks thunderstorm activity which may expose Sebastien to ingesting the cooler drier air behind the approaching front. I forecast Sebastien to transition into a non-tropical frontal cyclone along the front by 24 hours as Sebastien arrives into waters below 26 deg C. On the other hand the most recent satellite frames show an impressive expanding burst of thunderstorms wrapping into the nort half of the circulation...so it would not surprise me either if Sebastien indeed becomes a category 1 hurricane and still has fully tropical characteristics by 1200Z tomorrow. Regarding the track forecast...I have nudged mine southward again as yet again Sebastien remains further to the south than I previously forecasted. This...combined with the fact that Sebastien has continued to strengthen and will continue to be supported by the eastern divergence zone of the frontal upper trough after it transitions into non-tropical status...increases the chances that the western Azores could see gusty winds from the remnant frontal cyclone of Sebastien on Sunday...with all of the islands potentially seeing sea swells from the remnant cyclone.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Nov 21)...60 mph maximum sustained wind tropical storm merging with cold front at 23.5N-60.5W
IOH 24 Hr Forecast (1200Z Nov 22)...70 mph maximum sustained wind remnant frontal cyclone centered at 28.5N-54W