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Tropical Depression Sally Forecast Discussion


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000
WTNT44 KNHC 170831
TCDAT4

Tropical Depression Sally Discussion Number  25
NWS National Hurricane Center Miami FL       AL192020
400 AM CDT Thu Sep 17 2020

Although the overall convective cloud and rain shield in satellite 
and radar imagery continues to erode, Tropical Depression Sally is 
still producing significant rainfall across east-central Alabama 
and west-central and central Georgia.  Surface observations 
and Doppler radar data indicate that Sally has weakened to a 25-kt 
depression over southeastern Alabama.  Sally will continue to 
weaken, and fairly rapidly at that, due to increasing friction and 
loss of convection owing to very hostile westerly to southwesterly 
vertical wind shear in excess of 40 kt. Sally will likely 
degenerate into a remnant low pressure system by tonight or early 
Friday, and merge with a frontal system over North Carolina by 
Friday evening.

Sally is moving northeastward or 055/10 kt. A northeastward to 
east-northeastward motion will continue for the next 36 hours or 
so as the cyclone moves ahead of a broad deep-layer trough over the 
northeastern United States.  The official track forecast is down
the middle of the tightly packed NHC model guidance suite, and lies 
close to the previous advisory track and the consensus model HCCA.

This is the last NHC advisory on Sally.  Future information on this 
system, including the rainfall threat, can be found in Public 
Advisories issued by the Weather Prediction Center beginning at 
10 AM CDT, under AWIPS header TCPAT3, WMO header WTNT34 KWNH, and 
on the web at http://www.wpc.ncep.noaa.gov 


KEY MESSAGES:

1. Widespread flooding is expected from central Georgia through 
southeastern Virginia.  Along the central Gulf Coast, most 
widespread moderate to major river flooding from the historic 
rainfall event will crest by the weekend, but rivers will remain 
elevated well into next week.


FORECAST POSITIONS AND MAX WINDS

INIT  17/0900Z 31.8N  85.7W   25 KT  30 MPH...INLAND
 12H  17/1800Z 32.8N  84.2W   25 KT  30 MPH...INLAND
 24H  18/0600Z 34.0N  81.3W   20 KT  25 MPH...POST-TROP/REMNT LOW
 36H  18/1800Z 35.1N  78.4W   20 KT  25 MPH...POST-TROP/REMNT LOW
 48H  19/0600Z...MERGED WITH FRONTAL SYSTEM

$$
Forecaster Stewart