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Tropical Storm Gamma Discussion Number   4
NWS National Hurricane Center Miami FL       AL252020
400 AM CDT Sat Oct 03 2020

Satellite imagery and reports from an Air Force Reserve Hurricane 
Hunter aircraft indicate that Gamma is strengthening.  A central 
dense overcast with cloud tops to -85C has formed, along with an 
outer convective band in the eastern semicircle.  The aircraft has 
reported maximum 850 mb flight-level winds of 58 kt and reliable- 
looking surface wind estimates from the Stepped Frequency Microwave 
Radiometer of 40-45 kt.  Based on this, the initial intensity is 
increased to 45 kt.

The initial motion is again a little to the left of the previous 
advisory, 305/8 kt.  During the next 24-36 h, Gamma is expected to 
turn northward as it tries to recurve into a break in the 
subtropical ridge caused by a mid-latitude trough over the eastern 
United States.  The track guidance, however, is in good agreement 
that the trough will bypass the tropical cyclone, with a ridge 
building to the north after 36 h.  This should cause Gamma to turn 
westward or southwestward between the ridge and the Central 
American cyclonic gyre to the south.  There is uncertainty as to 
whether Gamma will move over the Gulf of Mexico before this turn 
occurs, as the ECMWF keeps the center inland or very near the 
coast.  The new forecast track is north of the ECMWF, but a little 
to the south of the previous track.  The foreast track calls for 
landfall on the northeastern Yucatan Peninsula in about 12 h, 
followed by the center reaching the Gulf of Mexico in about 36 h 
and a track near the coast of the Yucatan Peninsula thereafter.

Conditions appear favorable for strengthening until landfall, and 
the forecast 12-h intensity of 50 kt could be conservative given 
current trends.  The remainder of the intensity forecast is quite 
uncertain due to the possibility of land interaction, dry air 
entrainment, shear, and possible interaction with another system to 
the east.  The intensity guidance again does not show much 
strengthening if Gamma emerges into the Gulf of Mexico, and that 
part of the new intensity forecast has only minor adjustments from 
the previous one.  It should be noted that several models show a low 
pressure area over the northern Gulf of Mexico after 120 h.  Whether 
this will be Gamma or a new system is unclear at this time.
 
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 today and Sunday, where a Tropical Storm
Warning is in effect.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  03/0900Z 19.4N  86.9W   45 KT  50 MPH
 12H  03/1800Z 20.2N  87.4W   50 KT  60 MPH
 24H  04/0600Z 21.1N  87.9W   45 KT  50 MPH...INLAND
 36H  04/1800Z 21.7N  88.0W   40 KT  45 MPH...OVER WATER
 48H  05/0600Z 21.8N  88.4W   40 KT  45 MPH
 60H  05/1800Z 21.6N  89.3W   45 KT  50 MPH
 72H  06/0600Z 21.2N  90.5W   45 KT  50 MPH
 96H  07/0600Z 20.5N  92.4W   45 KT  50 MPH
120H  08/0600Z 19.5N  93.5W   40 KT  45 MPH
 
$$
Forecaster Beven
 
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