####018002689####
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