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Tropical Depression FIFTEEN


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TROPICAL DEPRESSION FIFTEEN DISCUSSION NUMBER   1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT MON SEP 05 2005

SATELLITE DATA DURING THE DAY INDICATE THAT THE LOW PRESSURE SYSTEM
SOUTH-SOUTHWEST OF BERMUDA HAS NOW ACQUIRED ENOUGH ORGANIZATION TO
BE STARTED AS TROPICAL DEPRESSION FIFTEEN. DEEP CONVECTION HAS
DEVELOPED NEAR AND TO THE EAST OF THE CENTER WHICH HAS MEANDERED IN
A CYCLONIC LOOP FOR MOST OF THE DAY.  BANDING FEATURES HAVE ALSO
BECOME MORE WELL DEFINED. THE SYSTEM LIES NEAR A MID/UPPER LEVEL
RIDGE AXIS WHICH EXTENDS SOUTHWEST FROM THE DEPRESSION TO THE
BAHAMAS...WITH GOOD UPPER LEVEL OUTFLOW IN THE SOUTHERN SEMICIRCLE.
THE RIDGE AXIS IS EXPECTED TO DRIFT NORTH OVER THE NEXT FEW
DAYS...WHICH SHOULD ALLOW FOR CONTINUED SLOW STRENGTHENING OF THE
CYCLONE THROUGH ABOUT 72 HOURS UNDER LIGHT SHEAR. BEYOND THIS
TIME...THE SYSTEM IS FORECAST TO GET CAUGHT IN THE WESTERLIES
ASSOCIATED WITH A LONGWAVE TROUGH MOVING OFF THE EASTERN U.S.
COAST. THIS SHOULD INCREASE THE SHEAR AND PUT AN END TO THE
INTENSIFICATION. SHIPS MODEL GUIDANCE FOLLOWS THIS TREND...PEAKING
THE INTENSITY AT 60 KT BEYOND 72 HOURS. THE OFFICIAL FORECAST IS
CLOSE TO SHIPS THROUGH 48 HOURS...THEN CONSERVATIVELY PEAKING AT 50
KT AT 72 HOURS AND BEYOND. THE SYSTEM COULD STRENGTHEN MORE THAN
INDICATED...ESPECIALLY DURING THE FIRST 72 HOURS UNDER THE
FAVORABLE UPPER LEVEL ENVIRONMENT.

AS MENTIONED ABOVE...THE DEPRESSION HAS MEANDERED IN A CYCLONIC LOOP
DURING THE PAST 6 HOURS AFTER A SLOW NORTHWEST MOTION LAST NIGHT.
BECAUSE OF THIS CHANGE IN THE SHORT TERM MOTION...THE INITIAL
INTENSITY IS SET TO STATIONARY. STEERING CURRENTS WILL REMAIN WEAK
FOR THE NEXT FEW DAYS AS THE MID/UPPER LEVEL RIDGE HOVERS NEAR THE
SYSTEM. BEYOND 72 HOURS...GLOBAL MODELS AGREE ON A LONGWAVE TROUGH
MOVING OFF THE EASTERN U.S. COAST. THIS SHOULD WEAKEN THE MID/UPPER
LEVEL RIDGE AND START TURNING THE CYCLONE TO THE NORTH AND
NORTHEAST BY THE END OF THE FORECAST PERIOD. TRACK GUIDANCE IS
QUITE SCATTERED AS CAN BE EXPECTED WITH A SYSTEM UNDER WEAK
STEERING CURRENTS...WITH THE GFS AND U.K. MET OFFICE MODELS MOVING
THE CYCLONE VERY LITTLE FOR ABOUT 48 HOURS...FOLLOWED BY A MOTION
TO THE NORTH AND NORTHEAST IN THE LATTER PORTION OF THE FORECAST.
THE NOGAPS MODEL MOVES THE SYSTEM FASTER TO THE WEST-NORTHWEST
THROUGH 72 HOURS BEFORE RECURVATURE. THE GFDL MODEL IS
SIMILAR...BUT  SLOWER...TO THE NOGAPS. THE FORECAST TRACK IS CLOSE
TO THAT OF THE GFDL...EXCEPT SOMEWHAT SLOWER DUE TO THE INITIAL
STATIONARY MOTION. 
 
FORECASTER MOLLEDA/PASCH
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      05/2100Z 27.8N  67.5W    25 KT
 12HR VT     06/0600Z 27.8N  67.5W    30 KT
 24HR VT     06/1800Z 27.9N  68.2W    35 KT
 36HR VT     07/0600Z 28.0N  69.0W    40 KT
 48HR VT     07/1800Z 28.3N  70.0W    45 KT
 72HR VT     08/1800Z 29.5N  72.0W    50 KT
 96HR VT     09/1800Z 31.0N  72.5W    50 KT
120HR VT     10/1800Z 32.0N  70.5W    50 KT
 
 
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