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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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