Tropical Depression THIRTEEN

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TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132011
1000 PM CDT THU SEP 01 2011
 
ALTHOUGH THE OVERALL SATELLITE PRESENTATION OF THE DEPRESSION HAS
CHANGED LITTLE THIS EVENING...NEW BANDS OF DEEP CONVECTION HAVE
DEVELOPED TO THE SOUTHEAST OF THE CENTER.  SATELLITE
CLASSIFICATIONS AND RECENT BUOY OBSERVATIONS SUPPORT KEEPING THE
INITIAL INTENSITY AT 30 KT.  A NOAA HURRICANE HUNTER AIRCRAFT IS
SCHEDULED TO INVESTIGATE THE CYCLONE OVERNIGHT.  A SHEAR ANALYSIS
FROM UW-CIMSS SHOWS ABOUT 20 KT OF WESTERLY SHEAR OVER THE
CYCLONE.  THIS SHEAR IS FORECAST TO RELAX DURING THE NEXT 12-24
HOURS AS AN UPPER-LEVEL ANTICYCLONE BUILDS OVER THE GULF.  THIS IS
EXPECTED TO RESULT IN A FAVORABLE ENVIRONMENT FOR INTENSIFICATION.
HOWEVER...GIVEN THE LARGE SIZE OF THE CIRCULATION...STRENGTHENING 
IS EXPECTED TO BE GRADUAL.  THE NEW NHC INTENSITY FORECAST IS
NEARLY IDENTICAL TO THE PREVIOUS ADVISORY AND IS A BLEND OF THE
SHIPS/LGEM GUIDANCE.

THE DEPRESSION HAS NOT MOVED MUCH THIS EVENING...AND THE HIGHLY
UNCERTAIN INITIAL MOTION IS 315/2 KT.   SINCE THE DEPRESSION IS
STILL IN THE FORMATIVE STAGE...THE CENTER COULD REFORM WITHIN THE
LARGE CIRCULATION DURING THE NEXT 12-24 HOURS.  THIS POSSIBILITY 
IS SUPPORTED BY THE GFS...WHICH SHOWS THE CENTER REFORMING FARTHER
NORTH WITHIN 24 HOURS.  STEERING CURRENTS ARE EXPECTED TO REMAIN
WEAK DURING THE NEXT SEVERAL DAYS AS THE DEPRESSION REMAINS TO THE
SOUTH OF A WEAKENING MID/UPPER LEVEL RIDGE.  AS THE RIDGE SLIDES
EASTWARD...IT SHOULD ALLOW THE CYCLONE TO MOVE SLOWLY NORTHWARD...
THEN NORTHEASTWARD.  ALTHOUGH THE DYNAMICAL MODELS SHOWS LITTLE
OVERALL MOTION DURING THE NEXT 2-3 DAYS...THERE IS A LARGE SPREAD
IN THE GUIDANCE AND LOWER THAN NORMAL CONFIDENCE IN THE TRACK
FORECAST.  THE UPDATED NHC TRACK IS A LITTLE SLOWER AND EAST OF 
THE PREVIOUS FORECAST. 
 
THE SLOW MOTION OF THE CYCLONE DURING THE NEXT 5 DAYS IS LIKELY
TO PRODUCE A PROLONGED PERIOD OF TROPICAL STORM CONDITIONS AND
HEAVY RAINFALL OVER PORTIONS OF THE NORTHERN GULF COAST.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  02/0300Z 26.6N  91.5W   30 KT  35 MPH
 12H  02/1200Z 27.5N  92.2W   35 KT  40 MPH
 24H  03/0000Z 28.0N  92.4W   40 KT  45 MPH
 36H  03/1200Z 28.6N  92.4W   45 KT  50 MPH
 48H  04/0000Z 29.2N  92.3W   50 KT  60 MPH
 72H  05/0000Z 29.7N  92.1W   50 KT  60 MPH...NEAR THE COAST
 96H  06/0000Z 30.5N  91.5W   35 KT  40 MPH...INLAND
120H  07/0000Z 31.5N  90.0W   25 KT  30 MPH...INLAND
 
$$
FORECASTER BROWN
 
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