Tropical Depression THIRTEEN

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TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL132007
500 PM EDT WED SEP 26 2007

THE CYCLONE'S CLOUD PATTERN IS WELL-ORGANIZED WITH DISTINCT BANDING
FEATURES OVER THE SOUTHERN SEMICIRCLE AND A FAIRLY SYMMETRIC
UPPER-LEVEL OUTFLOW.  SATELLITE-BASED INTENSITY ESTIMATES FROM TAFB
AND SAB ARE BOTH AT TROPICAL STORM STRENGTH.  HOWEVER...LOOKS CAN
BE DECEIVING...AND RECENT DATA FROM AN AIR FORCE HURRICANE HUNTER
MISSION INDICATE THAT THE SYSTEM IS NOT YET A TROPICAL STORM.  THE
ADVISORY INTENSITY REMAINS 30 KT...AND THIS MAY BE A GENEROUS
ESTIMATE SINCE THE HIGHEST FLIGHT-LEVEL WINDS WERE ONLY 29 KT. 
GIVEN THE ORGANIZATION OF THE SYSTEM...DECREASING SHEAR...AND VERY
WARM WATERS...STRENGTHENING IS LIKELY.  THE OFFICIAL WIND SPEED
FORECAST IS SIMILAR TO THE SHIPS GUIDANCE...AND COULD BE
CONSERVATIVE.

AIRCRAFT FIXES INDICATE THAT THE CYCLONE IS MEANDERING OR MAY BE
EXECUTING A COUNTERCLOCKWISE LOOP.  THE TRACK FORECAST REASONING IS
ABOUT THE SAME AS EARLIER TODAY.  A MID-TROPOSPHERIC RIDGE IS
EXPECTED TO BUILD EASTWARD GRADUALLY FROM NORTHERN MEXICO INTO THE
GULF OVER THE NEXT FEW DAYS.  THIS SHOULD EVENTUALLY STEER THE
TROPICAL CYCLONE IN A GENERALLY WESTWARD DIRECTION TOWARD THE COAST
OF MEXICO.  HOWEVER THE MODELS ARE NOT IN VERY GOOD AGREMMENT.  THE
U.K. MET. OFFICE MODEL TRACK IS ON THE NORTH SIDE OF THE GUIDANCE
SUITE WITH A WEST-NORTHWESTWARD MOTION ACROSS THE COAST IN ABOUT 66
HOURS.  THE HWRF MODEL KEEPS THE SYSTEM MEANDERING OFFSHORE AND
WEAKENS IT LATE IN THE FORECAST PERIOD.  THE GFDL MODEL SHOWS
LANDFALL IN ABOUT 36 HOURS...IN CONTRAST TO THE MUCH SLOWER ECMWF
WHICH DOES NOT SHOW THE CYCLONE CROSSING THE COASTLINE UNTIL NEARLY
84 HOURS.  THE OFFICIAL FORECAST IS ABOUT IN THE MIDDLE OF THESE
VARIOUS OBJECTIVE TRACKS.

THE MEANDERING MOTION DELAYS THE ISSUANCE OF A TROPICAL STORM WATCH
FOR THE GULF COAST OF MEXICO A LITTLE MORE...BUT THE WATCH COULD BE
ISSUED LATER TONIGHT OR EARLY TOMORROW. 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/2100Z 21.3N  94.5W    30 KT
 12HR VT     27/0600Z 21.2N  94.8W    35 KT
 24HR VT     27/1800Z 20.9N  95.1W    45 KT
 36HR VT     28/0600Z 20.7N  95.6W    50 KT
 48HR VT     28/1800Z 20.5N  96.3W    55 KT
 72HR VT     29/1800Z 20.2N  97.8W    20 KT...INLAND
 96HR VT     30/1800Z...DISSIPATED
 
$$
FORECASTER PASCH
 
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