Tropical Storm DORIAN

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TROPICAL STORM DORIAN DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042013
500 PM EDT WED JUL 24 2013
 
CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY INDICATE THAT THE
CONVECTIVE STRUCTURE OF DORIAN HAS CHANGED LITTLE SINCE THE
PREVIOUS ADVISORY. HOWEVER...UPPER-LEVEL ANTICYCLONIC OUTFLOW HAS
IMPROVED IN ALL QUADRANTS AS THE VERTICAL SHEAR HAS DIMINISHED
SIGNIFICANTLY. THE INITIAL INTENSITY OF 45 KT IS BASED ON A
SATELLITE INTENSITY ESTIMATE OF T3.0/45 KT FROM TAFB.
 
THE INITIAL MOTION ESTIMATE IS 285/17 KT. DORIAN IS EXPECTED TO
REMAIN SOUTH OF AND MOVE WEST-NORTHWESTWARD TO WESTWARD IN TANDEM
WITH A STRONG SUBTROPICAL RIDGE LOCATED WELL TO THE NORTH. THE NHC
MODEL GUIDANCE CONTINUES TO REMAIN TIGHTLY PACKED AND IN EXCELLENT
AGREEMENT ON THIS SCENARIO. THE ONLY DIFFERENCES IN THE MODELS ARE
THE FORWARD SPEED...WHICH IS DUE TO THE STRENGTH AND VERTICAL DEPTH
OF DORIAN. THE GFS...UKMET...AND CANADIAN MODELS MAINTAIN A ROBUST
AND MORE VERTICALLY DEEP CYCLONE...WHICH GETS STEERED MORE SLOWLY
BY THE DEEPER MEAN FLOW. IN CONTRAST...THE HWRF AND ECMWF MODELS
WEAKEN DORIAN SIGNIFICANTLY AS THE CYCLONE PASSES OVER COOLER WATER
DURING THE NEXT 48 HOURS...WHICH RESULTS IN A SHALLOWER AND WEAKER
VORTEX BEING STEERED MORE RAPIDLY WESTWARD BY THE STRONGER EASTERLY
TRADE WIND FLOW. GIVEN THAT DORIAN WILL BE MOVING OVER COOLER WATER
AT A BRISK 18 KT FOR THE NEXT 24-36 HOURS...MY FEELING IS THAT THE
CYCLONE WILL NOT WEAKEN AS MUCH AS THE SOME OF THE MODELS ARE
FORECASTING...AND AS A RESULT...THE OFFICIAL TRACK FORECAST LEANS
TOWARD THE SLOWER GFS...UKMET...AND CANADIAN MODEL SOLUTIONS.
 
DORIAN IS BEGINNING TO MOVE OVER SUB-26C SSTS...AND THE CYCLONE
SHOULD REMAIN OVER COOLER WATERS NEAR 25C FOR THE NEXT 12 HOURS
OR SO...WHICH COULD INDUCE SOME SLIGHT WEAKENING. HOWEVER...BY 36-48
HOURS...DORIAN WILL BE MOVING BACK OVER SSTS WARMER THAN 26C AND IN
A VERY LOW VERTICAL SHEAR ENVIRONMENT...WHICH SHOULD ALLOW FOR SOME
RE-STRENGTHENING TO OCCUR.  THE LATEST RUNS OF THE GFS AND ECMWF
ARE SHOWING A LESS HOSTILE UPPER-AIR PATTERN NEAR THE END OF THE
FORECAST PERIOD...WITH MORE RIDGING AND LESS INFLUENCE FROM AN
UPPER-LEVEL TROUGH OVER THE BAHAMAS.  IN CONSIDERATION OF THAT...
THE FORECAST INTENSITIES AT DAYS 4-5 HAVE BEEN INCREASED RELATIVE
TO THE PREVIOUS ADVISORY.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  24/2100Z 14.6N  31.4W   45 KT  50 MPH
 12H  25/0600Z 15.3N  34.0W   45 KT  50 MPH
 24H  25/1800Z 16.1N  37.5W   40 KT  45 MPH
 36H  26/0600Z 16.8N  41.0W   40 KT  45 MPH
 48H  26/1800Z 17.5N  44.7W   45 KT  50 MPH
 72H  27/1800Z 18.7N  51.8W   45 KT  50 MPH
 96H  28/1800Z 19.6N  58.9W   50 KT  60 MPH
120H  29/1800Z 20.0N  64.0W   50 KT  60 MPH
 
$$
FORECASTER STEWART
 
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