|Mesoscale Discussion 1690|
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Mesoscale Discussion 1690
NWS Storm Prediction Center Norman OK
1015 AM CDT Tue Sep 15 2020
Areas affected...Portions of coastal southern AL and the FL
Concerning...Tornado Watch 489...
Valid 151515Z - 151745Z
The severe weather threat for Tornado Watch 489 continues.
SUMMARY...The tornado threat should remain fairly limited over land
this morning, before gradually increasing along the immediate coast
DISCUSSION...Hurricane Sally remains about 110 miles south of Mobile
AL as of 15Z this morning, moving only very slowly northwest per the
latest NHC advisory. Easterly surface winds along the coast of AL
and the western FL Panhandle rapidly strengthen with height to
around 40-60 kt in the 0-1 km layer per recent VWPs from KMOB/KEVX.
Even though little veering/directional shear is noted, strong speed
shear of 40-45 kt in the 0-1 km layer is present across these areas.
Recent observations along/near the coast show surface dewpoints are
generally in the 72-76 degree F range. Widespread rain is also
ongoing, which will likely temper instability over land through the
remainder of the morning. Accordingly, the tornado threat over land
will probably remain limited for the next couple of hours. Greater
low-level moisture characterized by 77-79+ degree F surface
dewpoints will likely be needed to support weak MLCAPE and
surface-based storms along the coast. This moisture should increase
through the afternoon as Hurricane Sally moves ever so slowly
northward and low-level winds acquire a more southeasterly
component. Current expectations are for the isolated tornado threat
to gradually increase along the AL and FL Panhandle coasts later
this afternoon as low-topped supercells in outer rain bands move
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 30178831 30708829 30818755 30818614 30628514 30428472
29888440 29548507 29668539 29918550 30248599 30368657
30288721 30198786 30178831
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