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Hurricane RAFAEL


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HURRICANE RAFAEL DISCUSSION NUMBER  15
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL172012
500 AM AST TUE OCT 16 2012
 
LITTLE CHANGE IN THE OVERALL CONVECTIVE CLOUD PATTERN HAS OCCURRED
SINCE THE PREVIOUS ADVISORY. THERE IS ONE NOTICEABLE CHANGE...
HOWEVER...AND THAT IS THAT THE COLDEST CLOUD TOPS HAVE SHIFTED INTO
THE WESTERN SEMICIRCLE...WHICH HAS PROMPTED A SLIGHT INCREASE IN
THE 34- AND 50-KT WIND RADII IN THE NORTHWESTERN QUADRANT OF THE
CYCLONE. AN INTENSITY OF 75 KT IS BEING MAINTAINED FOR THIS
ADVISORY BASED ON A BLEND OF INTENSITY ESTIMATES OF T4.5/77 KT...
T4.0/65 KT...AND ADT CI OF T4.8/85 KT FROM TAFB...SAB...AND
UW-CIMSS...RESPECTIVELY. THE UPPER-LEVEL OUTFLOW IS GOOD IN ALL
QUADRANTS...EXCEPT RESTRICTED TO THE SOUTHWEST DUE TO 
SOUTHWESTERLY SHEAR OF MORE THAN 25 KT.

RAFAEL IS NOW MOVING NORTH-NORTHEASTWARD AT A SLIGHTLY FASTER
FORWARD SPEED...OR 015/14 KT. THE FORECAST TRACK AND RATIONALE
REMAINS UNCHANGED FROM THE PREVIOUS FEW ADVISORIES. RAFAEL IS
EXPECTED TO GRADUALLY TURN TOWARD THE NORTHEAST OVER THE NEXT 24
HOURS AS THE CYCLONE ROUNDS THE WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE ORIENTED EAST-TO-WEST ALONG 33-34N LATITUDE.
UPPER-AIR DATA AT 00Z FROM BERMUDA INDICATED 24-HOUR HEIGHT FALLS
OF 40-60 METERS FROM 700-400 MB...WHICH SUGGESTS THAT THE RIDGE IS
ERODING AS PREVIOUSLY EXPECTED. AS A LARGE MID-TROPOSPHERIC TROUGH
CURRENTLY ALONG THE U.S. EAST COAST APPROACHES RAFAEL LATER
TODAY...THE CYCLONE IS FORECAST TO ACCELERATE TO THE NORTHEAST AND
PASS JUST EAST OF BERMUDA BY TONIGHT AND WEDNESDAY MORNING. BY 48
HOURS...RAFAEL IS EXPECTED TO BE OVER MUCH COLDER WATER AND MERGE
WITH A STRONG COLD FRONT...WHICH SHOULD CAUSE THE CYCLONE TO
TRANSITION INTO A LARGE AND POWERFUL EXTRATROPICAL LOW THAT WILL
THEN MOVE EASTWARD OVER THE FAR NORTH ATLANTIC AND WELL AWAY FROM
CANADA. THE NHC TRACK FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY
TRACK...AND LIES DOWN THE MIDDLE OF THE TIGHTLY PACKED TRACK MODEL
GUIDANCE.

DUE TO INCREASING SOUTHWESTERLY VERTICAL WIND SHEAR...LITTLE CHANGE
IN STRENGTH IS EXPECTED TODAY...FOLLOWED BY A GRADUAL DECREASE IN
INTENSITY BY WEDNESDAY MORNING. RAFAEL IS EXPECTED TO UNDERGO
EXTRATROPICAL TRANSITION IN ABOUT 48 HOURS WHEN THE CYCLONE MERGES
WITH A STRONG COLD FRONT AND MOVES OVER SUB-20C SEA SURFACE
TEMPERATURES. HOWEVER...AND ABUNDANCE OF COLD AIR ALOFT ASSOCIATED
WITH THE DEEP-LAYER TROUGH APPROACHING THE CYCLONE SHOULD INDUCE
STRONG BAROCLINIC FORCING...WHICH WILL KEEP RAFAEL AS A POWERFUL
EXTRATROPICAL LOW PRESSURE SYSTEM FOR THE REMAINDER OF THE FORECAST
PERIOD. THE OFFICIAL INTENSITY FORECAST IS JUST AN UPDATE OF THE
PREVIOUS ADVISORY...AND CLOSELY FOLLOWS THE LGEM AND INTENSITY
MODEL CONSENSUS GUIDANCE. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  16/0900Z 26.6N  65.0W   75 KT  85 MPH
 12H  16/1800Z 29.4N  63.8W   75 KT  85 MPH
 24H  17/0600Z 33.8N  61.1W   70 KT  80 MPH
 36H  17/1800Z 38.8N  56.4W   65 KT  75 MPH
 48H  18/0600Z 43.3N  49.2W   60 KT  70 MPH...POST-TROP/EXTRATROP
 72H  19/0600Z 49.7N  32.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
 96H  20/0600Z 49.3N  28.1W   50 KT  60 MPH...POST-TROP/EXTRATROP
120H  21/0600Z 46.5N  28.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER STEWART
 
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