*******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 19 2019 1:29 PM EDT...
Central Atlantic surface low pressure spin northeast of the Lesser Antilles has strengthened into a tropical storm. See Tropical Storm Sebastien section below for additional details.
TROPICAL STORM SEBASTIEN...In the last 24 hours the central tropical Atlantic surface low pressure spin northeast of the Lesser Antilles has seen an improvement in upper-level winds that have allowed it to strengthen into the latest tropical storm of the 2019 Atlantic Hurricane Season. Specifically the latent heat release of the thunderstorms on the east side of the low pressure spin...perhaps in combination with warm air advection ahead of the western Atlantic frontal cyclone now moving across Newfoundland and Nova Scotia...have eroded a cold core upper trough in the region...with what is left of this upper trough now being an upper vortex to the east that is enhancing the eastern outflow of what is now Tropical Storm Sebastien. Another upper trough approaching from the western Atlantic is suppressing thunderstorms in the west half of Sebastien...but this trough is not able to significantly shear Sebastien due to the building outflow over the tropical storm induced by the ongoing latent heat release of the thunderstorms and is forecast to weaken while passing south of Sebastien and link with the upper vortex to the east while forced away by additional warming induced by warm air advection (northward warm air transport) on the east side of a new frontal low developing in the western Atlantic. However I do not forecast Sebastien to briskly strengthen before a cold front driven by this new frontal low absorbs the tropical storm because there are no intense thunderstorm bursts currently covering the circulation center...and also because there will be some southwesterly shear as the large upper trough supporting the frontal low (currently over the eastern US) approaches from the west. However I do forecast a peak strength of 60 mph maximum sustained winds in 48 hours just before Sebastien merges with the cold front as the increasing north and then northeast forecast track will be increasingly in alignment with the upper southwesterly winds which may help in reducing the shear...and the divergence zone on the east side of the approaching large upper trough may also aid Sebastien during this time.
******Infohurricanes.com forecast. Visit hurricanes.gov (hurricanes dot gov) for official forecast***********
0 Hr Position (1200Z Nov 19)...45 mph maximum sustained wind tropical storm centered northeast of the northern Lesser Antilles at 20.1N-58.7W
IOH 24 Hr Forecast (1200Z Nov 20)...50 mph maximum sustained wind tropical storm centered at 24N-59.5W
IOH 48 Hr Forecast (1200Z Nov 21)...60 mph maximum sustained wind tropical storm merging with cold front at 28N-57W
IOH 72 Hr Forecast (1200Z Nov 22)...Remnant frontal low centered at 32N-54W