Tropical Depression THIRTEEN

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TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132011
400 AM CDT FRI SEP 02 2011

SATELLITE IMAGERY...SURFACE OBSERVATIONS...AND AN EARLIER ASCAT
OVERPASS INDICATE THAT TROPICAL DEPRESSION THIRTEEN HAS A ELONGATED
CENTER OF CIRCULATION...WITH THE ELONGATION CURRENTLY FROM
EAST-NORTHEAST TO WEST-SOUTHWEST.  THE ASSOCIATED CONVECTION IS
CURRENTLY POORLY ORGANIZED...ALTHOUGH A STRONG BURST HAS RECENTLY
FORMED NEAR THE EAST-NORTHEASTERN END OF THE CENTER.  THE INITIAL
INTENSITY REMAINS 30 KT BASED ON THE ASCAT OVERPASS AND REPORTS
FROM OIL RIGS IN THE NORTHERN GULF.  WHILE THERE IS GOOD OUTFLOW
OVER THE EASTERN SEMICIRCLE...AN UPPER-LEVEL TROUGH IS PRESENT OVER
THE WESTERN SIDE OF THE CIRCULATION.

THE DEPRESSION HAS NOT MOVED MUCH DURING THE PAST SEVERAL HOURS...
WITH THE INITIAL MOTION A HIGHLY UNCERTAIN 315/2.  THE CYCLONE IS
CURRENTLY IN AN AREA OF LIGHT STEERING CURRENTS SOUTH OF A
MID-LEVEL RIDGE OVER THE MISSISSIPPI VALLEY.  THE DYNAMICAL MODELS
FORECAST THIS RIDGE TO MOVE EASTWARD AND WEAKEN AS A DEEP-LAYER
TROUGH MOVES SOUTHEASTWARD INTO THE OHIO VALLEY.  THIS EVOLUTION
SHOULD ALLOW THE DEPRESSION TO MOVE SLOWLY NORTHWESTWARD TO
NORTHWARD FOR THE NEXT 24-36 HR...FOLLOWED BY A GRADUAL TURN TOWARD
THE NORTHEAST.  MOST OF THE DYNAMICAL MODELS NOW SHOW THIS
SCENARIO...ALTHOUGH THERE REMAINS ENOUGH DISAGREEMENT BETWEEN THEM
TO KEEP THIS A LOW CONFIDENCE FORECAST.  THE NEW FORECAST TRACK IS
ADJUSTED SOUTH AND EAST OF THE PREVIOUS FORECAST BASED MAINLY ON
THE INITIAL POSITION...AND LIES CLOSE TO THE VARIOUS CONSENSUS
MODELS FOR THE FIRST THREE DAYS OF THE FORECAST.  IT SHOULD BE
NOTED THAT REFORMATIONS OF THE CENTER COULD CAUSE ERRATIC MOTION
AND ADJUSTMENTS TO THE FORECAST TRACK DURING THE NEXT COUPLE OF
DAYS.

THE CURRENT INTERACTION WITH THE UPPER-LEVEL TROUGH IS FORECAST BY
THE DYNAMICAL MODELS TO CONTINUE FOR AT LEAST THE NEXT COUPLE OF
DAYS...RESULTING IN VERTICAL WIND SHEAR CONDITIONS THAT...AT
BEST...WILL BE MARGINALLY FAVORABLE FOR INTENSIFICATION.  THIS
INTERACTION...COMBINED WITH THE CURRENT ORGANIZATION OF THE
SYSTEM...SUGGESTS THAT STRENGTHENING SHOULD BE SLOW.  THE NEW
INTENSITY FORECAST IS UNCHANGED FROM THE PREVIOUS ADVISORY AND LIES
BETWEEN THE STRONGER SHIPS AND WEAKER LGEM MODELS.
 
THE LARGE SIZE AND 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  02/0900Z 26.5N  91.7W   30 KT  35 MPH
 12H  02/1800Z 27.0N  92.1W   35 KT  40 MPH
 24H  03/0600Z 27.6N  92.3W   40 KT  45 MPH
 36H  03/1800Z 28.2N  92.2W   45 KT  50 MPH
 48H  04/0600Z 28.8N  92.0W   50 KT  60 MPH
 72H  05/0600Z 29.5N  91.5W   50 KT  60 MPH...INLAND
 96H  06/0600Z 30.5N  90.0W   40 KT  45 MPH...INLAND
120H  07/0600Z 31.5N  88.5W   25 KT  30 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BEVEN
 
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