Tropical Depression THIRTEEN

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TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL132007
1100 PM EDT WED SEP 26 2007
 
THE SATELLITE PRESENTATION OF THE DEPRESSION HAS DEGRADED THIS
EVENING...WITH A PARTIALLY EXPOSED CENTER TO THE NORTHEAST OF A
SMALL BAND OF MODEST CONVECTION.  DVORAK T-NUMBERS FROM BOTH TAFB
AND SAB HAVE DECREASED.  THE INITIAL INTENSITY WILL BE HELD AT 30
KT PENDING THE ARRIVAL OF THE NEXT RECONNAISSANCE AIRCRAFT AT 06Z.

THE DEPRESSION APPEARS TO HAVE COMPLETED A SMALL LOOP...AND THE
INITIAL MOTION IS ESTIMATED TO BE 260/3...BASED MAINLY ON A 2315Z
MICROWAVE PASS.  THERE HAS BEEN A BIT OF A NORTHWARD SHIFT IN THE
MODEL GUIDANCE THIS EVENING.  THE MID-LEVEL RIDGE THAT IS FORECAST
TO BUILD EASTWARD FROM NORTHERN MEXICO HAS SHIFTED A LITTLE FARTHER
EASTWARD IN THE MODEL RUNS...WHICH ALLOWS THE DEPRESSION TO ACQUIRE
SOME NORTHWARD COMPONENT OF MOTION AS IT APPROACHES THE COAST.  THE
OFFICIAL FORECAST HAS BEEN SHIFTED NORTHWARD...AND IS IN BEST
AGREEMENT WITH THE GFS.  NEARLY ALL THE OTHER GUIDANCE MODELS ARE
EVEN FARTHER NORTH.

THE UPPER-LEVEL FLOW OVER THE DEPRESSION IS ANTICYCLONIC AND
DIFLUENT...AND IT IS A LITTLE SURPRISING THAT THE SYSTEM HAS NOT
STRENGTHENED YET.  THE UPPER-FLOW IS FORECAST TO REMAIN FAVORABLE
FOR DEVELOPMENT...SO PERHAPS IT IS JUST A MATTER OF TIME.  THE
OFFICIAL FORECAST REMAINS CLOSE TO THE SHIPS GUIDANCE...WITH THE
GFDL AND HWRF FORECASTING A LITTLE LESS DEVELOPMENT BUT STILL
MAKING THE SYSTEM A TROPICAL STORM.

THE NEW FORECAST BRINGS TROPICAL STORM FORCE WINDS VERY CLOSE TO THE
MEXICAN COAST IN 36 HOURS...NECESSITATING A TROPICAL STORM WATCH AT
THIS TIME.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/0300Z 21.2N  94.8W    30 KT
 12HR VT     27/1200Z 21.1N  95.0W    35 KT
 24HR VT     28/0000Z 20.9N  95.5W    45 KT
 36HR VT     28/1200Z 20.9N  96.3W    50 KT
 48HR VT     29/0000Z 21.0N  97.5W    55 KT...INLAND
 72HR VT     30/0000Z 21.5N  99.5W    20 KT...INLAND
 96HR VT     01/0000Z...DISSIPATED
 
$$
FORECASTER FRANKLIN
 
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