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Tropical Storm RAFAEL


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TROPICAL STORM RAFAEL DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL172012
1100 PM AST FRI OCT 12 2012

RAFAEL HAS A RATHER DISORGANIZED APPEARANCE IN SATELLITE IMAGERY
THIS EVENING.  THE BROAD LOW-LEVEL CENTER IS LOCATED TO THE WEST OF
THE MAIN CONVECTIVE MASS DUE TO 20-25 KT OF SOUTHWESTERLY VERTICAL
WIND SHEAR.  LESS CONCENTRATED CONVECTION IS OCCURRING TO THE
NORTHWEST OF THE CENTER.  THERE HAVE BEEN NO OBSERVATIONS OF
TROPICAL-STORM-FORCE WINDS FROM THE LESSER ANTILLES...BUT IT IS
LIKELY THAT SUCH WINDS ARE LOCATED IN THE CONVECTIVE BAND EAST AND
SOUTHEAST OF THE CENTER.  THE INITIAL INTENSITY REMAINS 35 KT IN
AGREEMENT WITH THE SATELLITE INTENSITY ESTIMATE FROM TAFB.

THE INITIAL MOTION IS A RATHER UNCERTAIN 325/9.  RAFAEL IS CURRENTLY
SOUTHEAST OF A LARGE BREAK IN THE SUBTROPICAL RIDGE CAUSED BY
TROPICAL DEPRESSION PATTY...A FRONTAL SYSTEM...AND A MID/UPPER-
LEVEL TROUGH.  THIS SYNOPTIC PATTERN SHOULD STEER RAFAEL GENERALLY
NORTH-NORTHWESTWARD FOR THE NEXT 24-36 HR...WITH THE CENTER PASSING
NEAR THE VIRGIN ISLANDS IN ABOUT 24 HOURS.  THE GLOBAL MODELS
FORECAST A LOW/MID-LEVEL RIDGE TO BRIEFLY BUILD NORTH OF RAFAEL AT
ABOUT 48 HR...WHICH WILL SUBSEQUENTLY BREAK DOWN AS A POWERFUL
DEEP-LAYER TROUGH MOVES INTO THE WESTERN ATLANTIC.  THIS TROUGH
SHOULD RECURVE RAFAEL INTO THE WESTERLIES.  WHILE THE GLOBAL MODELS
AGREE ON THIS...THEY DIFFER ENOUGH ON THE DETAILS THAT THE GFS AND
CANDIAN SHOW A MUCH FASTER FORWARD MOTION AFTER RECURVATURE THAN
THE ECMWF AND UKMET.  THE NEW TRACK FORECAST FOLLOWS THE PREVIOUS
FORECAST IN SPLITTING THE DIFFERENCE BETWEEN THESE EXTREMES. 
OVERALL...THE NEW FORECAST TRACK IS CLOSE TO THE OLD TRACK AND NEAR
THE CENTER OF THE GUIDANCE ENVELOPE.

LITTLE CHANGE IN STRENGTH IS EXPECTED DURING THE FIRST 12 HR DUE TO
CONTINUED SHEAR.  AFTER THAT...THE GLOBAL MODELS FORECAST A
DECREASE IN SHEAR FROM 24-48 HR...WITH THE INTENSITY GUIDANCE
SHOWING INTENSIFICATION DURING THIS TIME.  THE INTENSITY FORECAST
DURING THIS PERIOD IS NEAR THE INTENSITY CONSENSUS.  THE GLOBAL
MODELS AGREE ON INCREASING SHEAR AFTER 48 HR.  DESPITE THIS...THE
GFDL...HWRF...AND SHIP MODELS FORECAST RAFAEL TO STRENGTHEN INTO A
HURRICANE.  THE INTENSITY FORECAST WILL RELY MORE ON THE FORECAST
SHEAR AND SHOW ARRESTED DEVELOPMENT AFTER 48 HR.  EXTRATROPICAL
TRANSITION SHOULD BEGIN BY 120 HR AND LIKELY BE COMPLETE SHORTLY
THEREAFTER.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  13/0300Z 15.4N  63.4W   35 KT  40 MPH
 12H  13/1200Z 16.6N  63.9W   35 KT  40 MPH
 24H  14/0000Z 18.4N  64.3W   40 KT  45 MPH
 36H  14/1200Z 20.3N  65.0W   50 KT  60 MPH
 48H  15/0000Z 22.1N  66.1W   55 KT  65 MPH
 72H  16/0000Z 26.0N  67.0W   55 KT  65 MPH
 96H  17/0000Z 34.5N  63.5W   55 KT  65 MPH
120H  18/0000Z 44.5N  55.5W   50 KT  60 MPH
 
$$
FORECASTER BEVEN
 
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