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Tropical Storm Gamma Discussion Number   9
NWS National Hurricane Center Miami FL       AL252020
1000 AM CDT Sun Oct 04 2020

An Air Force Reserve reconnaissance aircraft has found the center 
of Gamma over the far southern Gulf of Mexico, just north of the 
Yucatan Peninsula.  Early morning visible satellite imagery has 
revealed decent banding structure over the northern and western 
portions of the circulation.  The aircraft has measured a peak 850 
mb flight-level wind of 66 kt and SFMR winds of 47 kt.  A blend of 
these data support an initial intensity of 50 kt, which is also in 
line with the latest Dvorak classifications of T3.0 and T3.5 from 
SAB and TAFB, respectively. 

Gamma appears to be slowing down as anticipated, with an initial 
motion estimate of 360/3 kt.  Gamma is expected to meander over the 
southern Gulf of Mexico, just north of the northern coast of the 
Yucatan peninsula during the next 12-24 hours.  By late Monday, the 
western portion of a subtropical ridge is expected to build 
westward over the northern Gulf of Mexico.  This should cause Gamma 
to turn westward to west-southwestward through the remainder of the 
forecast period.  The dynamical model guidance is in general 
agreement on this scenario, but there are some differences in how 
close Gamma tracks to the northwestern portion of the Yucatan 
peninsula.  The NHC track splits these differences and is a blend 
TCVA multi-model consensus and the HFIP corrected consensus.  The 
new track forecast is very close to the previous official forecast. 

Although Gamma has re-strengthened this morning, increasing 
southerly wind shear is expected over the cyclone by tonight.  
This unfavorable upper-level environment is likely to cause 
some gradual weakening by late tonight and Monday.  Since the 
vertical shear expected to remain moderate to strong through the 
latter portion of the forecast period, little overall change in 
strength is shown after 48 hours. 

 
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 northern coast of the Yucatan 
Peninsula today.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  04/1500Z 22.2N  88.2W   50 KT  60 MPH
 12H  05/0000Z 22.6N  88.2W   50 KT  60 MPH
 24H  05/1200Z 22.6N  88.5W   45 KT  50 MPH
 36H  06/0000Z 22.3N  89.3W   40 KT  45 MPH
 48H  06/1200Z 22.0N  90.2W   40 KT  45 MPH
 60H  07/0000Z 21.5N  91.0W   40 KT  45 MPH
 72H  07/1200Z 21.0N  91.6W   40 KT  45 MPH
 96H  08/1200Z 20.4N  92.5W   40 KT  45 MPH
120H  09/1200Z 20.4N  93.0W   40 KT  45 MPH
 
$$
Forecaster Brown
 
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