Official Discussion issued by the National Hurricane Center

Gamma (AL252020) DATA RELEASED: 10/2/2020 10:00:00 PM UTC

Copy of official data

Tropical Storm Gamma Discussion Number   3
NWS National Hurricane Center Miami FL       AL252020
1000 PM CDT Fri Oct 02 2020

A few hours ago, the Air Force Hurricane Hunters found maximum
winds of around 35 kt in the northeastern quadrant of the cyclone,
which was the reason why it was upgraded to Tropical Storm Gamma.
Since then, there have been no stronger winds reported so the
initial intensity remains 35 kt.  The minimum pressure estimated by
the aircraft is quite low at 998 mb, so it seems likely that
the winds will increase soon.  The storm also has better banding
features compared to hours ago and deep convection has also been
persisting near the center.

Fixes from the aircraft indicate that Gamma has jogged to the left 
recently, but smoothing through the short-term jog suggests an 
initial motion of 310/8 kt.  The tropical storm is expected to 
remain on the western periphery of a subtropical high during the 
next couple of days, and that should cause the storm to move slowly 
northwestward during that time period.  This track should take Gamma 
across the northern Yucatan Peninsula and perhaps over the extreme 
south-central Gulf of Mexico this weekend. By early next week, a 
mid-level ridge is expected to build to the north of the storm while 
another low pressure area is forecast to develop to the east of 
Gamma. This change in the steering pattern is expected to cause the 
storm to make a sharp left turn toward the Bay of Campeche, but 
continue to move at a fairly slow forward speed. The models have 
shifted well to the south from 48-120 hours this cycle, and the NHC 
track forecast has been adjusted in that direction.  Despite the 
shift, most of the reliable models are south of the new official 
track forecast, and future southward adjustments could be necessary.

Environmental conditions appear generally favorable for additional
strengthening until the cyclone reaches the Yucatan Peninsula on
Saturday, and the NHC intensity forecast shows a slightly higher
landfall intensity there.  Once the system moves over the Yucatan
Peninsula and the extreme southern Gulf of Mexico, the combination
of land interaction, an increase in shear, and drier air should
limit the amount of strengthening into next week.  At this point,
no model shows Gamma becoming a hurricane, and the NHC intensity
forecast shows little change in strength for much of the forecast
period.

The biggest threat from this large and slow-moving storm is the
the potential for heavy rainfall and flooding, particularly near
and over mountainous terrain.


KEY MESSAGES:

1. Gamma is expected to produce heavy rainfall that could result in
life-threatening flash flooding over portions of the Yucatan
Peninsula, far western Cuba and well away from the center in
the Mexican states of Campeche, Tabasco, and northern Chiapas.

2. Gamma is forecast to bring tropical storm conditions to portions
of the Yucatan Peninsula on Saturday, where a Tropical Storm
Warning is in effect.


FORECAST POSITIONS AND MAX WINDS

INIT  03/0300Z 19.1N  86.1W   35 KT  40 MPH
12H  03/1200Z 19.8N  86.9W   45 KT  50 MPH
24H  04/0000Z 20.8N  87.6W   45 KT  50 MPH...INLAND
36H  04/1200Z 21.6N  88.0W   40 KT  45 MPH...INLAND
48H  05/0000Z 22.0N  88.3W   40 KT  45 MPH
60H  05/1200Z 21.9N  88.9W   40 KT  45 MPH
72H  06/0000Z 21.7N  90.0W   45 KT  50 MPH
96H  07/0000Z 21.0N  91.8W   45 KT  50 MPH
120H  08/0000Z 20.3N  92.8W   45 KT  50 MPH

$$
Forecaster Cangialosi