[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 121436
TCDAT4

Tropical Storm Sean Discussion Number   7
NWS National Hurricane Center Miami FL       AL192023
1100 AM AST Thu Oct 12 2023

Sean remains a poorly organized tropical cyclone on visible and
infrared satellite imagery this morning. The low-level center is
exposed on GOES-16 1-minute visible imagery, and displaced to the
west of the main convective band. The overall satellite appearance
has resulted in subjective Dvorak data-T numbers of T1.5/T2.0 from
TAFB and SAB, respectively. However, recent scatterometer passes
from both ASCAT-B and ASCAT-C depict a swath of
tropical-storm-force winds to the northeast of the center. Given
this scatterometer data, the initial intensity is raised back to 35
kt for this advisory, making Sean a tropical storm once again.

The tropical storm is moving northwestward at 305/8 kt. A weak low-
to mid-level ridge to the north and northeast of Sean should steer
the cyclone west-northwestward or northwestward throughout the
forecast period. There was a nudge to the right with the latest
model track guidance, and the NHC track has been adjusted slightly
right accordingly, and lies near the simple and corrected consensus
aids.

Westerly vertical wind shear is expected to persist over the system
for the next day or so. This shear is forecast to then decrease
along Sean's forecast track. However, the system will also be moving
into a drier airmass and less favorable upper-level environment.
Simulated satellite imagery from the GFS and ECMWF models suggest
that Sean could struggle to produce organized convection in the
coming days. While small intensity fluctuations are possible, as
seen this morning, the NHC intensity forecast remains near the HCCA
and IVCN consensus aids, keeping Sean a tropical storm the next day
or so, then weakening back into a depression once again. Afterwards,
the system is forecast to degenerate into a post-tropical remnant
low and dissipate into a trough by day 4. Some of the global models
suggest that each of these transitions could occur even sooner than
what is shown in the official forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 13.1N  37.2W   35 KT  40 MPH
 12H  13/0000Z 13.5N  38.4W   35 KT  40 MPH
 24H  13/1200Z 14.4N  40.1W   35 KT  40 MPH
 36H  14/0000Z 15.6N  41.6W   30 KT  35 MPH
 48H  14/1200Z 16.9N  42.9W   30 KT  35 MPH
 60H  15/0000Z 18.2N  44.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  15/1200Z 19.0N  45.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  16/1200Z...DISSIPATED

$$
Forecaster Kelly
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