Tropical Storm Gamma Forecast Discussion


000
WTNT45 KNHC 040232
TCDAT5

Tropical Storm Gamma Discussion Number   7
NWS National Hurricane Center Miami FL       AL252020
1000 PM CDT Sat Oct 03 2020

Tropical Storm Gamma remains over the northern portion of the
Yucatan Peninsula, and the cyclone has been inland for about 10
hours now.  Although the storm has weakened some, satellite images
show that Gamma still has an intact central dense overcast feature
and spiral bands on the north side of the circulation.  The initial
intensity is estimated to be 50 kt, but there is quite of bit of
uncertainty in this value.  The tropical storm is drenching the
northern portion of the Yucatan Peninsula, and heavy rainfall is
likely to continue there into Sunday.

The tropical storm is moving northwestward at 6 kt on the
southwestern periphery of an Atlantic subtropical ridge.  Gamma is
expected to move very slowly to the northwest or north-northwest
toward a weakness in the ridge during the next 12 to 24 hours, and
that should take the core of the tropical storm over the extreme
southern Gulf of Mexico by early Sunday.  By Sunday night and
Monday, a combination of a building low- to mid-level ridge over the
Gulf of Mexico and a developing low pressure area over the
northwestern Caribbean Sea should cause Gamma to turn fairly sharply
to the west or southwest early next week.  A slow southwest or west
motion is likely to continue into the middle of next week, and some
of the models suggest that Gamma could become nearly stationary by
the end of the forecast period.  The NHC track forecast is largely
an update of the previous one and lies near the TVCA and HCCA
consensus models.

The intensity forecast seems tricky.  The tropical storm still
appears well organized despite its time over land and since it will
be moving back over water soon, it could re-strengthen.  However,
none of the intensity models show much strengthening, in fact, most
of them show Gamma gradually weakening throughout the forecast
period.  On one hand, the storm is going to be over the warm Gulf
of Mexico waters for several days, which favors strengthening. On
the other hand, there is a fair amount of dry air over the western
Gulf of Mexico and this could entrain into the circulation. Another
complicated factor is how Gamma interacts with a developing low over
the northwestern Caribbean Sea and a disturbance to its south.
Based on these complexities, the NHC intensity forecast shows no
change in strength through the forecast period, and lies near the
high end of the guidance near the SHIPS model.

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 inland, tropical storm conditions will
continue across portions of the Yucatan Peninsula tonight
and Sunday.


FORECAST POSITIONS AND MAX WINDS

INIT  04/0300Z 21.3N  88.0W   50 KT  60 MPH
 12H  04/1200Z 21.8N  88.2W   50 KT  60 MPH
 24H  05/0000Z 22.2N  88.5W   50 KT  60 MPH
 36H  05/1200Z 22.1N  88.9W   50 KT  60 MPH
 48H  06/0000Z 21.8N  89.9W   50 KT  60 MPH
 60H  06/1200Z 21.3N  90.9W   50 KT  60 MPH
 72H  07/0000Z 20.7N  91.7W   50 KT  60 MPH
 96H  08/0000Z 20.0N  92.5W   50 KT  60 MPH
120H  09/0000Z 19.9N  93.3W   50 KT  60 MPH

$$
Forecaster Cangialosi

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