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Tropical Depression THIRTEEN (Text)

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TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132012
1100 PM EDT MON SEP 03 2012
 
THE CLOUD PATTERN OF THE DEPRESSION HAS NOT CHANGED MUCH IN
ORGANIZATION THIS EVENING. THE CENTER OF THE SYSTEM APPEARS TO
BE NEAR OR JUST UNDER THE WESTERN EDGE OF A RATHER LINEAR BAND OF
SHALLOW CONVECTION...SUGGESTIVE OF NORTHWESTERLY SHEAR. DVORAK
T-NUMBERS ARE AT 2.0 FROM TAFB AND SAB...SO THE INITIAL INTENSITY
ESTIMATE IS HELD AT 30 KT.  THE DEPRESSION IS OVER WARM WATERS AND
REMAINS EMBEDDED IN AN UPPER-LEVEL TROUGH WHERE THE SHEAR IS
RELATIVELY LOW.  AS THIS FEATURE LIFTS OUT DURING THE NEXT DAY OR
SO...STRONG NORTHWESTERLY FLOW ASSOCIATED WITH AN INTENSE SHORTWAVE
TROUGH SOUTHEAST OF THE CANADIAN MARITIME PROVINCES IS FORECAST TO
IMPINGE ON THE DEPRESSION.  THIS IS EVIDENCED BY CROSS-SECTION
ANALYSES OF THE ECMWF/GFS MODELS WHICH SHOW A CONSIDERABLE
SOUTHEASTWARD TILT OF THE VORTEX WITH HEIGHT.  THE ABRUPT INCREASE
IN SHEAR SHOULD BE SUBSTANTIAL ENOUGH TO CAUSE WEAKENING...
ESPECIALLY FOR A SMALL SYSTEM SUCH AS THIS ONE.  THE NHC INTENSITY
FORECAST IS UNCHANGED FROM THE PREVIOUS ONE...CONSERVATIVELY
SHOWING REMNANT LOW STATUS IN 3 DAYS.
 
SATELLITE DATA SUGGEST AN INITIAL MOTION ESTIMATE OF 305/04.  THE
DEPRESSION IS MOVING SLOWLY NORTHWESTWARD AROUND THE WESTERN
PERIPHERY OF A SUBTROPICAL RIDGE TO THE EAST...AND SHOULD TURN
NORTH-NORTHWESTWARD AND NORTHWARD DURING THE NEXT DAY OR TWO AS A
SHORTWAVE PASSES TO THE NORTH AND ERODES THE RIDGE FURTHER. THE
OFFICIAL TRACK FORECAST IS NEAR THE PREVIOUS ONE THROUGH 48 HOURS
AND IS ADJUSTED TO THE RIGHT AFTER THAT...IN GOOD AGREEMENT WITH
THE LATEST HWRF MODEL.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  04/0300Z 25.9N  42.8W   30 KT  35 MPH
 12H  04/1200Z 26.3N  43.3W   35 KT  40 MPH
 24H  05/0000Z 27.0N  44.1W   35 KT  40 MPH
 36H  05/1200Z 27.8N  44.5W   30 KT  35 MPH
 48H  06/0000Z 28.5N  44.3W   25 KT  30 MPH
 72H  07/0000Z 29.5N  44.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  08/0000Z 31.0N  44.0W   15 KT  15 MPH...POST-TROP/REMNT LOW
120H  09/0000Z...DISSIPATED
 
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FORECASTER KIMBERLAIN
 
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