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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
   Panhandle

   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
   this afternoon.

   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
   onshore.

   ..Gleason.. 09/15/2020

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...TAE...MOB...

   LAT...LON   30178831 30708829 30818755 30818614 30628514 30428472
               29888440 29548507 29668539 29918550 30248599 30368657
               30288721 30198786 30178831 

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Page last modified: September 15, 2020
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