Official Discussion issued by the National Hurricane Center

Gamma (AL252020) DATA RELEASED: 10/4/2020 4:00:00 PM UTC

Copy of official data

Tropical Storm Gamma Discussion Number  10
NWS National Hurricane Center Miami FL       AL252020
400 PM CDT Sun Oct 04 2020

The last aircraft reconnaissance fix, recorded a couple of hours 
ago, indicated that Gamma's center had wobbled a little to the 
right of the previous 6-hour motion and is located near the 
southeastern edge of the convective canopy.  Flight-level winds 
adjusted to the surface, SFMR wind data, and a blend of Dvorak 
satellite intensity estimates from TAFB and SAB still support an 
initial intensity of 50 kt for this advisory.

The UW-CIMSS shear analysis reveals stiff 20-25 kt southerly shear
impinging on the south portion of the cyclone.  Subsequently, the
large-scale models and the ECMWF/GFS statistical-dynamical
intensity guidance show the shear magnitude increasing during the
next 24 hours.  This inhibiting upper wind pattern should induce
weakening soon.  Although the shear is predicted to decrease
somewhat around mid-period, Gamma should exhibit little change in
strength through the remaining period which is in best agreement 
with all of the skilled intensity guidance.  As mentioned in 
previous advisories, it cannot be stressed enough the relatively 
high level of uncertainty in this intensity forecast, and that it's 
primarily dependent on whether or not the cyclone moves back over 
the Yucatan Peninsula.

Gamma should continue to move little, or meander over the
southern Gulf of Mexico, near the northern coast of the
Yucatan Peninsula through most of tomorrow.  By Monday night,
the global models are in good agreement with the western extent of 
a subtropical ridge reestablishing temporarily over the central 
Gulf of Mexico.  This change in the synoptic steering pattern 
should cause the cyclone to turn and move west-southwestward 
through the 72 hour forecast period.  After a brief reduction in 
forward speed late Wednesday, while Potential-Tropical Cyclone 
Twenty-Six moves into the central Gulf of Mexico, a turn toward the 
northwest is expected on Thursday as the ridge, once again, builds 
back over the central Gulf in response to PTC Twenty-Six 
approaching the northern Gulf coast.  The official track forecast 
is adjusted to the left of the previous one through the 60 hour 
period to agree more with the HCCA consensus, and shifted to the    
right through day 5. 


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 just offshore, tropical storm conditions 
will continue across portions of the northern coast of the Yucatan
Peninsula today.


INIT  04/2100Z 22.4N  87.8W   50 KT  60 MPH
12H  05/0600Z 22.3N  88.1W   45 KT  50 MPH
24H  05/1800Z 22.1N  88.6W   40 KT  45 MPH
36H  06/0600Z 21.7N  89.4W   40 KT  45 MPH
48H  06/1800Z 21.3N  90.4W   40 KT  45 MPH
60H  07/0600Z 20.8N  91.1W   40 KT  45 MPH
72H  07/1800Z 20.1N  91.4W   40 KT  45 MPH
96H  08/1800Z 21.0N  92.1W   40 KT  45 MPH
120H  09/1800Z 22.2N  92.7W   40 KT  45 MPH

Forecaster Roberts