Tropical Depression THIRTEEN

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TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL132007
1100 AM EDT WED SEP 26 2007

THERE HAS BEEN AN INCREASE IN DEEP CONVECTION AND ORGANIZATION OF
THE DEPRESSION'S CLOUD PATTERN OVER THE PAST SEVERAL HOURS.  DVORAK
SATELLITE CLASSIFICATIONS FROM TAFB AND SAB ARE AT 30 AND 35 KT
RESPECTIVELY.  WE WILL WAIT FOR THE NEXT AIR FORCE HURRICANE HUNTER
FIX SCHEDULED FOR 1800 UTC TO SEE IF THE SYSTEM HAS INDEED
STRENGTHENED INTO A TROPICAL STORM.  AN UPPER-LEVEL CYCLONE IN THE
VICINITY OF TUXPAN MEXICO IS MOVING SOUTHWESTWARD...AND AWAY FROM
THE TROPICAL CYCLONE...CREATING AN ENVIRONMENT THAT IS MORE
FAVORABLE FOR STRENGTHENING.  CIRRUS MOTIONS SHOW THAT THE
ANTICYCLONIC OUTFLOW IS BECOMING BETTER ESTABLISHED OVER THE
SYSTEM.  THE OFFICIAL INTENSITY FORECAST...WHICH IS SIMILAR TO THE
SHIPS AND GFDL GUIDANCE...COULD BE CONSERVATIVE...PARTICULARLY IF
THE TROPICAL CYCLONE REMAINS OVER WATER LONGER THAN EXPECTED.

THE INITIAL MOTION IS AN UNCERTAIN 180/2.  A WEAK STEERING CURRENT
HAS PREVAILED OVER THE SOUTHWESTERN GULF OF MEXICO OVER THE PAST
COUPLE OF DAYS...AND THE DEPRESSION WILL PROBABLY MOVE QUITE SLOWLY
AND ERRATICALLY TODAY.  GLOBAL MODELS FORECAST A WEAK MID-LEVEL
RIDGE TO BUILD EASTWARD SLOWLY FROM NORTHERN MEXICO OVER THE GULF
OF MEXICO.  THIS SHOULD EVENTUALLY RESULT IN A SOUTHWESTWARD TO
WESTWARD MOTION OF THE TROPICAL CYCLONE TOWARD THE COAST OF MEXICO.  
ALTHOUGH THE CONSENSUS OF THE TRACK GUIDANCE MODELS INDICATES THE
ABOVEMENTIONED MOTION...THERE ARE SIGNIFICANT DIFFERENCES AMONGST
THE INDIVIDUAL MODELS.  IT SHOULD BE NOTED... HOWEVER...THAT ALL OF
THE DYNAMICAL MODELS KEEP THE SYSTEM OFFSHORE THROUGH 36 HOURS. 
THE OFFICIAL FORECAST FOLLOWS THE CONSENSUS AND IS SIMILAR TO THE
TRACK FORECAST FROM THE PREVIOUS NHC PACKAGE.

A TROPICAL STORM WATCH WILL LIKELY BE REQUIRED FOR A PORTION OF THE
GULF COAST OF MEXICO LATER TODAY.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/1500Z 20.9N  95.0W    30 KT
 12HR VT     27/0000Z 20.7N  95.1W    35 KT
 24HR VT     27/1200Z 20.5N  95.4W    40 KT
 36HR VT     28/0000Z 20.3N  95.9W    45 KT
 48HR VT     28/1200Z 20.1N  96.6W    50 KT
 72HR VT     29/1200Z 20.0N  97.7W    20 KT...INLAND
 96HR VT     30/1200Z...DISSIPATED
 
$$
FORECASTER PASCH
 
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