Tropical Storm DORIAN

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TROPICAL STORM DORIAN DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042013
500 AM AST SAT JUL 27 2013

DISORGANIZED CONVECTION HAS DEVELOPED NEAR THE CENTER OF DORIAN
DURING THE PAST SEVERAL HOURS.  HOWEVER...WATER VAPOR IMAGERY SHOWS
WIDESPREAD MID-/UPPER-LEVEL DRY AIR NEAR THE CYCLONE...WHICH
SUGGESTS THIS CONVECTION COULD BE SHORT-LIVED.  THE INITIAL
INTENSITY IS KEPT AT 35 KT BASED ON A SATELLITE INTENSITY ESTIMATE
FROM TAFB AND EARLIER ASCAT DATA.  IT SHOULD BE NOTED THAT RECENT
OSCAT DATA SUGGESTS THE POSSIBILITY THAT DORIAN NO LONGER HAS A
CLOSED CIRCULATION.  
 
THE INITIAL MOTION IS 275/19.  A STRONG LOW-/MID-LEVEL RIDGE NORTH
OF DORIAN IS EXPECTED TO STEER THE CYCLONE QUICKLY WESTWARD FOR THE
NEXT 72 HR.  THE TRACK GUIDANCE IS IN GOOD AGREEMENT WITH THIS
SCENARIO...AND THE NEW TRACK FORECAST IS AN UPDATE OF THE PREVIOUS
FORECAST.
 
DORIAN IS FORECAST TO EXPERIENCE 15-20 KT OF VERTICAL WIND SHEAR
DURING THE FORECAST PERIOD...AS WELL AS MOVE THROUGH A DRY
MID-/UPPER-LEVEL AIR MASS.  THIS COMBINATION SHOULD CAUSE
ADDITIONAL WEAKENING...WITH THE CYCLONE DEGENERATING TO A REMNANT
LOW BY 36 HR.  AN ALTERNATIVE SCENARIO IS THAT THE SYSTEM COULD
DEGENERATE TO A TROPICAL WAVE AT ANY TIME DURING THE NEXT 72 HR...
AND THUS DISSIPATE EARLIER THAN CURRENTLY FORECAST.  UPPER-LEVEL
WINDS IN THE AREA WEST OF THE FORECAST POINT OF DISSIPATION ARE NOT
EXPECTED TO BE CONDUCIVE FOR RE-GENERATION AT THIS TIME.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0900Z 18.2N  50.0W   35 KT  40 MPH
 12H  27/1800Z 18.6N  53.1W   30 KT  35 MPH
 24H  28/0600Z 19.2N  57.2W   30 KT  35 MPH
 36H  28/1800Z 19.8N  61.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  29/0600Z 20.4N  64.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  30/0600Z 21.0N  71.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  31/0600Z...DISSIPATED
 
$$
FORECASTER BEVEN
 
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