Tropical Depression THIRTEEN

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TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL132007
1100 PM EDT TUE SEP 25 2007
 
THE CENTER OF THE DEPRESSION IS DIFFICULT TO LOCATE IN CONVENTIONAL
IMAGERY...BUT AN SSMI MICROWAVE PASS JUST BEFORE 00Z DEPICTED THE
SMALL CENTER NICELY AND INDICATES THAT THE INITIAL MOTION IS 260/4. 
STEERING CURRENTS ARE WEAK...AND LITTLE OVERALL MOTION IS EXPECTED
OVER THE NEXT DAY OR TWO.  SOME OF THE MODELS ROTATE THE DEPRESSION
WITHIN A BROADER LOW-LEVEL CYCLONIC FLOW IN THE SOUTHWESTERN GULF
UNTIL MID-LEVEL RIDGING DEVELOPS OVER THE CENTRAL GULF IN A COUPLE
OF DAYS.  GIVEN THE INTERMITTENT NATURE OF THE CONVECTION...AND
GLOBAL MODEL GUIDANCE SUGGESTING THAT A FAVORABLE UPPER FLOW
PATTERN MAY TAKE A COUPLE DAYS TO DEVELOP...A SHORT-TERM LOOPING
SCENARIO MIGHT BE A REASONABLE ONE.

DEEP CONVECTION HAS BEEN CYCLING TODAY...AND IS PRESENTLY AT A
MINIMUM. THERE IS STILL SOME SOUTHWESTERLY SHEAR OVER THE
DEPRESSION ASSOCIATED WITH AN UPPER LOW ALONG THE MEXICAN COAST
NEAR TAMPICO. THIS SHEAR IS EXPECTED TO RELAX AND BE REPLACED BY AN
UPPER ANTICYCLONE OVER THE NEXT COUPLE OF DAYS...WHICH WOULD ALLOW
THE SYSTEM AN OPPORTUNITY TO STRENGTHEN. HOWEVER...NOT MUCH
DEVELOPMENT IS EXPECTED UNTIL THAT OCCURS. THE LATEST RUN OF THE
GFDL SHOWS A LITTLE MORE DEVELOPMENT THAN THE PREVIOUS RUN AND IS
NOW IN REASONABLE AGREEMENT WITH THE SHIPS GUIDANCE. THE LATEST
OFFICIAL FORECAST STRENGTHENS THE CYCLONE SLIGHTLY LESS QUICKLY
THAN THE PREVIOUS ADVISORY.  


FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/0300Z 21.7N  95.4W    25 KT
 12HR VT     26/1200Z 21.5N  95.5W    25 KT
 24HR VT     27/0000Z 21.3N  95.4W    30 KT
 36HR VT     27/1200Z 21.1N  95.3W    35 KT
 48HR VT     28/0000Z 20.9N  95.6W    40 KT
 72HR VT     29/0000Z 20.5N  96.5W    50 KT
 96HR VT     30/0000Z 20.0N  98.0W    30 KT...INLAND
120HR VT     01/0000Z...DISSIPATED
 
$$
FORECASTER FRANKLIN
 
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