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Tropical Storm Sebastien Discussion Number   6
NWS National Hurricane Center Miami FL       AL202019
500 PM AST Wed Nov 20 2019

Sebastien has changed little in organization today, with
northwesterly shear displacing the deep convection to the southeast
of an exposed low-level center. An ASCAT-C overpass late this
morning sampled peak winds of 41 kt, and so the initial advisory
intensity will remain 45 kt due to the assumption of undersampling
by the scatterometer.

Sebastien made its anticipated turn to the north earlier today, and
the current motion is now 360/05 kt. The cyclone should turn to the
northeast tonight and begin to accelerate as it gets embedded in
increasing southwesterly flow ahead of an approaching cold front and
associated mid- to upper- level trough. The official forecast track
is near the previous one through 24 hours, and a little slower and
to the south of it beyond that time due to a shift in the model
guidance.

The approaching trough should provide a diffluent environment aloft
over Sebastien beginning tonight and persisting until the system
makes the transition to an extratropical cyclone in a couple of
days. This is expected to result in some intensification over the
next day or so. Once extratropical, the cyclone should gradually
become absorbed into a frontal zone through the end of the week. The
official forecast is changed little from the previous one, and is
near the IVCN consensus.


FORECAST POSITIONS AND MAX WINDS

INIT  20/2100Z 21.7N  61.5W   45 KT  50 MPH
 12H  21/0600Z 22.7N  61.0W   50 KT  60 MPH
 24H  21/1800Z 24.5N  59.0W   60 KT  70 MPH
 36H  22/0600Z 27.2N  55.5W   60 KT  70 MPH
 48H  22/1800Z 30.0N  51.4W   60 KT  70 MPH...POST-TROP/EXTRATROP
 72H  23/1800Z...DISSIPATED

$$
Forecaster Latto

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