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Tropical Storm Marty Discussion Number   4
NWS National Hurricane Center Miami FL       EP132021
800 PM PDT Mon Aug 23 2021
 
Northeasterly vertical wind shear continues to disrupt the 
organization of Marty. The limited shower activity associated with 
the cyclone remains displaced to the southwest of its exposed 
low-level center. Despite its poor satellite appearance for much of 
the day, earlier scatterometer data showed 35 to 40-kt winds in the 
sheared cyclone. The latest objective satellite estimates and 
subjective Dvorak classifications support an intensity of 35 kt. 
However, the initial intensity for this advisory is conservatively 
held at 40 kt, with hopes that new scatterometer data become 
available overnight to better reassess Marty's intensity.

Marty is moving westward, or 270/15 kt. The subtropical ridge to the 
north of Marty will continue to steer the cyclone generally westward 
over the next couple days. Then, the weakening cyclone is forecast 
to turn west-southwestward during the latter part of the week within 
the low-level trade wind flow. The latest NHC track forecast is 
adjusted just a bit south of the previous one, near the middle of 
the guidance envelope and close to the multi-model consensus aids. 

Despite the modest wind shear values diagnosed from the SHIPS 
guidance, Marty is clearly struggling to maintain organized 
convection. Furthermore, Marty only has a brief window over 
sufficiently warm SSTs before it crosses the 26 deg C isotherm on 
Tuesday and moves into a drier, more stable airmass. Therefore, 
gradual weakening is expected to begin on Tuesday and continue 
through the rest of the week. In fact, the latest global model 
simulated satellite imagery suggests Marty could struggle to 
generate any organized convection beyond tonight's convective 
maximum period. The latest NHC intensity forecast is essentially 
unchanged. Marty is forecast to weaken to a depression by early 
Wednesday, degenerate into a remnant low by Wednesday night, and 
dissipate late this week. But, it is possible these changes could 
occur even sooner than forecast if Marty's convective structure does 
not improve soon.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/0300Z 20.7N 115.8W   40 KT  45 MPH
 12H  24/1200Z 20.7N 117.8W   35 KT  40 MPH
 24H  25/0000Z 20.7N 119.9W   35 KT  40 MPH
 36H  25/1200Z 20.7N 121.8W   30 KT  35 MPH
 48H  26/0000Z 20.7N 123.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  26/1200Z 20.5N 126.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  27/0000Z 20.1N 128.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  28/0000Z 18.7N 133.1W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  29/0000Z...DISSIPATED
 
$$
Forecaster Reinhart/Pasch
 
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