531
WTNT45 KNHC 051455
TCDAT5

Tropical Storm Gamma Discussion Number 13
NWS National Hurricane Center Miami FL AL252020
1000 AM CDT Mon Oct 05 2020

Air Force Reserve reconnaissance aircraft investigating Gamma found
maximum 850 mb flight-level winds of 37 kt and surface SFMR peak
winds of 40 kt, and the central pressure has increased to 1003 mb.
Therefore, the initial intensity is lowered to 40 kt for this
advisory.

Stiff, persistent southerly shear, and an inhibiting thermodynamic
surrounding environment should prevent Gamma from restrengthening,
although, the Decay SHIPS intensity model does indicate a very
brief period of decreasing shear magnitude just prior to landfall
around the 24 hour period. Afterward, the shear, once again,
increases. Gamma is expected to make landfall over the
northwestern Yucatan peninsula on Tuesday and further weakening
to a remnant low is forecast Wednesday as the cyclone remains
inland over the northern Mexican State of Yucatan. Dissipation is
likely to occur Friday over the region, if not sooner.

The initial motion is estimated to be a south-southwestward drift,
or 205/2 kt. A turn southwestward or west-southwestward is
expected by tonight and this general motion should continue through
Wednesday morning while moving inland over the northern Mexican
State of Yucatan. The large-scale models still insist on some
binary interaction occurring with Tropical Storm Delta commencing
Tuesday night/Wednesday morning. This should cause Gamma to
gradually turn cyclonically through Thursday while remaining over
the Northern Yucatan peninsula. If there is a delay in Gamma's
landfall, or the cyclone does remain just offshore, similar to the
outlier UKMET, then Tropical Storm Delta could end up absorbing the
smaller Gamma tropical cyclone toward the end of the week. For
now, the NHC forecast will side with a landfall scenario which
agrees with the HCCA consensus and the GFS/ECMWF solutions.

KEY MESSAGES:

1. Gamma is expected to produce heavy rainfall through midweek over
portions of southeast Mexico, including the Mexican states of
Yucatan, Campeche, and Tabasco. This rainfall could result in
significant flash flooding.

2. Even though Gamma is just offshore, tropical storm conditions
are likely along portions of the northern coast of the Yucatan
Peninsula later today.


FORECAST POSITIONS AND MAX WINDS

INIT 05/1500Z 22.3N 87.6W 40 KT 45 MPH
12H 06/0000Z 22.1N 88.4W 40 KT 45 MPH
24H 06/1200Z 21.6N 89.2W 35 KT 40 MPH
36H 07/0000Z 20.9N 89.9W 30 KT 35 MPH...INLAND
48H 07/1200Z 20.2N 90.2W 25 KT 30 MPH...POST-TROP/INLAND
60H 08/0000Z 20.3N 89.8W 25 KT 30 MPH...POST-TROP/INLAND
72H 08/1200Z 21.0N 89.5W 20 KT 25 MPH...POST-TROP/INLAND
96H 09/1200Z...DISSIPATED

$$
Forecaster Roberts
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