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| #550426 (Received by flhurricane at: 4:53 AM 16.Oct.2012) TCDAT2 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 |
