Tropical Depression THIRTEEN

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TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL132007
500 AM EDT WED SEP 26 2007
 
AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING
TROPICAL DEPRESSION THIRTEEN REPORTED MAXIMUM WINDS OF 26 KT AT A
FLIGHT LEVEL OF 1500 FT...ALONG WITH A CENTRAL PRESSURE OF
1007-1008 MB.  SATELLITE IMAGERY SHOWS AN INCREASE ON CONVECTION
EAST OF THE CENTER DURING THE PAST FEW HOURS...WHICH HAS RESULTED IN
SATELLITE INTENSITY ESTIMATES OF 30 KT FROM TAFB AND SAB.  BASED ON
THE AIRCRAFT DATA...THE INITIAL INTENSITY REMAINS 25 KT. 

THE HURRICANE HUNTER FOUND THE CENTER ABOUT 40 NM MI SOUTH-SOUTHEAST 
OF THE PREVIOUS ADVISORY POSITION...AND IT IS UNCLEAR HOW MUCH OF
THIS IS MOTION AND HOW MUCH IS REFORMATION OF THE CENTER.  THE
INITIAL MOTION IS A RATHER UNCERTAIN 180/3.  ALL MODEL GUIDANCE
AGREES THAT THE CYCLONE SHOULD MOVE LITTLE DURING THE NEXT 12-24
HR...WITH PERHAPS SOME SMALL-SCALE LOOPING OF THE CENTER.  AFTER
THAT...A MID-LEVEL RIDGE BUILDING EASTWARD FROM NORTHERN MEXICO
SHOULD STEER THE DEPRESSION TOWARD THE COAST OF MEXICO.  THE GFS
AND EUROPEAN MODELS SHOW A SOUTHWARD MOTION...WHILE THE UKMET AND
HWRF MODELS SHOW A WESTWARD MOTION.  THE NEW FORECAST TRACK
COMPROMISES BETWEEN THESE EXTREMES BY SHOWING A WEST-SOUTHWESTWARD
MOTION AFTER 24 HR...WITH THE CENTER REACHING THE COAST OF MEXICO
IN ABOUT 48 HR...ABOUT A DAY EARLIER THAN PREVIOUSLY FORECAST.  THE
NEW TRACK IS SHIFTED SOUTH OF THE PREVIOUS TRACK BASED MAINLY ON
THE INITIAL POSITION.

WATER VAPOR IMAGERY SHOWS AN UPPER-LEVEL LOW CENTERED NEAR TUXPAN
MEXICO.  THE LARGE-SCALE MODELS FORECAST THIS FEATURE TO MOVE
SOUTHWARD OR SOUTHWESTWARD AWAY FROM THE DEPRESSION...ALLOWING AN
UPPER-LEVEL ANTICYCLONE TO BUILD OVER THE SYSTEM WITH LIGHT
VERTICAL SHEAR.  THIS EVOLUTION SHOULD ALLOW THE DEPRESSION TO
STRENGTHEN UNTIL IT MAKES LANDFALL....AND THE INTENSITY FORECAST
THUS CALLS FOR STEADY STRENGTHENING TO 45 KT IN AGREEMENT WITH THE
SHIPS MODEL.  SHOULD THE DEPRESSION STAY OFFSHORE LONGER THAN
CURRENTLY FORECAST...IT COULD GET STRONGER THAN 45 KT BEFORE LAND.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/0900Z 21.0N  95.0W    25 KT
 12HR VT     26/1800Z 20.8N  94.9W    30 KT
 24HR VT     27/0600Z 20.6N  94.9W    35 KT
 36HR VT     27/1800Z 20.3N  95.7W    40 KT
 48HR VT     28/0600Z 20.1N  96.6W    45 KT
 72HR VT     29/0600Z 20.0N  98.0W    25 KT...INLAND
 96HR VT     30/0600Z...DISSIPATED
 
$$
FORECASTER BEVEN
 
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