Tropical Storm Sebastien Forecast Discussion Number 15

By | November 23, 2019

Issued at 1100 PM AST Fri Nov 22 2019

WTNT45 KNHC 230237

Tropical Storm Sebastien Discussion Number  15
NWS National Hurricane Center Miami FL       AL202019
1100 PM AST Fri Nov 22 2019

There is not much that I can add that my predecessors have not
already addressed except to say that Sebastien does not know that
is November near Thanksgiving.

One interesting aspect tonight is that although the cloud pattern
has not change at all today with the low-level center on the
southern edge of the convection due to shear, and with the same
Dvorak numbers, ASCAT data that just arrived showed numerous vectors
of 50 kt and a few near 55 kt.  On this basis, the initial intensity
has been adjusted upward to 55 kt in this advisory.

Sebastien has to weaken since is heading toward a hostile
environment of increasing shear and cooler waters. It might not do
it tonight, but the weakening process must begin within the next 24
hours or so. Both the GFS and the ECMWF open up the circulation
beyond 48 hours, and with the hostile environment ahead, the NHC
forecast calls for gradual weakening and dissipation in 3 days.

The cyclone is moving toward the northeast of 055 degrees at 13 kt.
Sebastien is embedded within the mid-latitude westerly flow, and the
cyclone has nowhere to go but to continue moving northeastward
with increasing forward speed. Models vary in speed, but on average
they all suggest acceleration.


INIT  23/0300Z 27.0N  52.2W   55 KT  65 MPH
 12H  23/1200Z 28.2N  50.2W   55 KT  65 MPH
 24H  24/0000Z 30.5N  46.5W   45 KT  50 MPH
 36H  24/1200Z 32.6N  42.5W   40 KT  45 MPH
 48H  25/0000Z 35.5N  36.0W   35 KT  40 MPH
 72H  26/0000Z...DISSIPATED

Forecaster Avila

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