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Tropical Storm Gamma Discussion Number   8
NWS National Hurricane Center Miami FL       AL252020
400 AM CDT Sun Oct 04 2020
 
Tropical Storm Gamma has moved back over open water, just offshore 
the northern Yucatan Peninsula in the extreme southern Gulf of 
Mexico. Although deep convection has been increasing near the 
center, the overall convective cloud shield is now strung out to 
the north and northeast due to southerly to southwesterly vertical 
wind shear in excess of 15 kt. The initial intensity of 45 kt is 
based on an earlier ASCAT pass showing 39-kt surface winds just 
offshore the northeastern tip of Yucatan, and these winds were 
likely under-sampled due to their proximity to the coast. Satellite 
classifications from both TAFB and SAB were T3.0/45 kt, which 
further supports the 45-kt intensity assessment.

The initial motion estimate is 355/04 kt. As the day progresses, 
Gamma is expected to move further into a slight weakness in 
subtropical ridge located to the north of the cyclone and slow down, 
possibly stalling by this afternoon. The trough over the 
southeastern U.S. that is creating the weakness is forecast to move 
offshore the U.S. east coast by tonight, causing the ridge to build 
back in and force Gamma westward to west-southwestward from Monday 
through Thursday. The new NHC track forecast follows the TVCA and 
FSSE consensus models, and is similar to but slightly slower and a 
little to the right/north of the previous advisory track. 
 
Now that Gamma is back out over open water, some slight 
re-strengthening is expected today. However, strong southerly 
vertical wind shear is forecast to increase across the cyclone by 
tonight and especially on Monday, and continue for the next few 
days. The result should be a slow but gradual weakening trend on 
Monday through the end of the forecast period. The new official 
intensity forecast follow the downward trend of the simple- and 
corrected-consensus models, but is slightly higher than the IVCN, 
HCCA, FSSE intensity models.
 
KEY MESSAGES:
 
1. Gamma is expected to produce heavy rainfall for several days over
portions of southeastern Mexico, the Yucatan Peninsula, Central
America, and far western Cuba.  This rainfall could result in
life-threatening flash flooding and mudslides, particularly in the
mountainous regions of southeastern Mexico and Central America.
 
2. Even though Gamma is offshore, tropical storm conditions will
continue across portions of the Yucatan Peninsula today.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  04/0900Z 22.0N  88.2W   45 KT  50 MPH
 12H  04/1800Z 22.6N  88.3W   50 KT  60 MPH
 24H  05/0600Z 22.7N  88.6W   45 KT  50 MPH
 36H  05/1800Z 22.4N  89.4W   45 KT  50 MPH
 48H  06/0600Z 22.0N  90.2W   40 KT  45 MPH
 60H  06/1800Z 21.5N  90.9W   40 KT  45 MPH
 72H  07/0600Z 21.0N  91.6W   40 KT  45 MPH
 96H  08/0600Z 20.4N  92.5W   40 KT  45 MPH
120H  09/0600Z 20.4N  93.4W   40 KT  45 MPH
 
$$
Forecaster Stewart
 
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