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Tropical Storm RAFAEL (Text)

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TROPICAL STORM RAFAEL DISCUSSION NUMBER   8
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL172012
1100 AM AST SUN OCT 14 2012
 
THE SATELLITE PRESENTATION OF RAFAEL IS GRADUALLY IMPROVING.  THE
CENTER IS LOCATED NEAR THE SOUTHWESTERN EDGE OF A BURST OF
CONVECTION WITH SEVERAL BANDS OF THUNDERSTORMS EVIDENT OVER THE
EASTERN PORTION OF THE LARGE CIRCULATION.  A U.S. AIR FORCE RESERVE
HURRICANE HUNTER AIRCRAFT HAS RECENTLY REPORTED A MINIMUM PRESSURE
OF 997 MB...WHICH IS SEVERAL MILLIBARS LOWER THAN 12 HOURS AGO.  
THE AIRCRAFT IS CURRENTLY SAMPLING THE NORTHEASTERN PORTION OF THE
STORM. FOR THE FIRST TIME...STRONG WINDS WERE MEASURED TO THE
NORTHWEST OF THE CENTER ON A PASS EARLIER THIS MORNING.  THE
AIRCRAFT REPORTED PEAK 925 MB FLIGHT-LEVEL WINDS OF 57 KT...AND
RAIN CORRECTED SFMR VALUES OF AROUND 45 KT.  BASED OF THIS
DATA...AND THE ASSUMPTION THAT STRONGER WINDS ARE LIKELY OCCURRING
TO THE NORTHEAST OF THE CENTER...THE INITIAL WIND SPEED IS
INCREASED TO 50 KT.
 
RAFAEL IS FORECAST TO REMAIN IN MODERATE SOUTHWESTERLY SHEAR DURING
THE NEXT DAY OR TWO.  HOWEVER...THE SHEAR IS NOT IS EXPECTED TO BE
STRONG ENOUGH TO PREVENT GRADUAL INTENSIFICATION.  NEARLY ALL OF
THE INTENSITY GUIDANCE BRINGS RAFAEL TO HURRICANE STRENGTH WITHIN
THE NEXT COUPLE OF DAYS AND SO DOES THE NHC FORECAST.  AFTER 48
HOURS...THE SHEAR IS EXPECTED TO INCREASE...WHICH SHOULD INDUCE
SOME WEAKENING.  RAFAEL WILL LIKELY BEGIN ITS TRANSITION TO AN
EXTRATROPICAL CYCLONE WITHIN 72 HOURS AS IT STARTS TO INTERACT A
MID-LATITUDE TROUGH THAT IS ANTICIPATED TO MOVE OVER THE WESTERN
ATLANTIC. THE EXTRATROPICAL TRANSITION SHOULD BE COMPLETE WITHIN 96
HOURS AND THIS IS REFLECTED IN THE OFFICIAL FORECAST.
 
THE INITIAL MOTION ESTIMATE IS 335/10 KT. RAFAEL IS FORECAST TO MOVE
NORTH-NORTHWESTWARD...THEN NORTHWARD AROUND THE WESTERN SIDE OF A
DEEP-LAYER RIDGE OVER THE CENTRAL ATLANTIC DURING THE NEXT COUPLE
OF DAYS. AFTER THAT TIME...A MID- TO UPPER-LEVEL TROUGH AND AN
ASSOCIATED COLD FRONT ARE EXPECTED TO MOVE OFF THE U.S. EAST COAST
AND INTO THE WESTERN ATLANTIC.  THIS SHOULD CAUSE THE TROPICAL
CYCLONE TO BEGIN ACCELERATING NORTHEASTWARD IN THE STRONG
SOUTHWESTERLY FLOW AHEAD OF THE TROUGH. THE TRACK GUIDANCE IS IN
GOOD AGREEMENT ON THIS SCENARIO...HOWEVER THERE ARE SOME SPEED
DIFFERENCES AMONG THE MODELS.  THE ECMWF CONTINUES TO BE MUCH
SLOWER THAN ALL OF THE GUIDANCE AS IT KEEPS RAFAEL WEAKER AND
SHALLOWER.  THE NHC FORECAST IS NEAR THE MIDDLE OF THE GUIDANCE
ENVELOPE...BUT LEANS TOWARD THE FASTER GFS/GFDL SOLUTION.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  14/1500Z 20.0N  64.1W   50 KT  60 MPH
 12H  15/0000Z 21.5N  65.1W   55 KT  65 MPH
 24H  15/1200Z 23.2N  66.2W   60 KT  70 MPH
 36H  16/0000Z 25.5N  66.2W   65 KT  75 MPH
 48H  16/1200Z 29.1N  64.8W   70 KT  80 MPH
 72H  17/1200Z 38.7N  58.5W   65 KT  75 MPH
 96H  18/1200Z 48.5N  48.0W   60 KT  70 MPH...POST-TROP/EXTRATROP
120H  19/1200Z 50.5N  40.5W   55 KT  65 MPH...POST-TROP/EXTRATROP
 
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FORECASTER BROWN
 
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