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| #457964 (Received by flhurricane at: 10:44 PM 08.Sep.2011) TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 44 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 1100 PM AST THU SEP 08 2011 THE CONVECTIVE PATTERN OF KATIA HAS IMPROVED SIGNIFICANTLY DURING THE PAST 6 HOURS...AND AN EYE HAS BECOME APPARENT AND EMBEDDED WITHIN A SHIELD OF CLOUD TOPS OF -60C AND COLDER. NHC AODT SATELLITE INTENSITY ESTIMATES FOR A LARGE RAGGED EYE FEATURE ARE 75-80 KT. GIVEN THAT THE OVERALL STRUCTURE IS BETTER NOW THAN IT WAS ON THE PREVIOUS ADVISORY...THE INITIAL INTENSITY WILL BE MAINTAINED AT 75 KT FOR THIS ADVISORY...WHICH MIGHT BE A LITTLE CONSERVATIVE. UPPER-LEVEL OUTFLOW IS EXCELLENT IN ALL QUADRANTS. KATIA IS MOVING TO THE NORTHEAST NOW...AND THE INITIAL MOTION ESTIMATE IS 035/18. KATIA HAS ROUNDED THE WESTERN PERIPHERY OF A LARGE SUBTROPICAL RIDGE ORIENTED EAST-WEST ALONG 33N LATITUDE AND IS BEGINNING TO ACCELERATE. ALL OF THE NHC MODEL GUIDANCE IS IN VERY GOOD AGREEMENT THAT KATIA WILL CONTINUE TO MOVE NORTHEASTWARD WITH A GRADUAL INCREASE IN FORWARD SPEED FOR THE NEXT 24-36 HOURS. ONCE THE CYCLONE PASSES NORTH OF 40N LATITUDE...IT IS EXPECTED TO GET CAUGHT UP IN VERY FAST WESTERLIES FOR THIS TIME OF THE YEAR AND ACCELERATE TO THE EAST-NORTHEAST AND EAST AT FORWARD SPEEDS OF NEAR 50 KT. ONCE KATIA MOVES OVER MUCH COLDER WATER BY 36 HOURS... THE COMBINATION OF THE FAST MID-LATITUDE FLOW AND SSTS LESS THAN 21C ARE EXPECTED TO RESULT IN THE TROPICAL CYCLONE MAKING THE TRANSITION INTO A POWERFUL EXTRATROPICAL CYCLONE. THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY...AND CLOSELY FOLLOWS THE NHC CONSENSUS MODELS TVCN AND TVCA. NOW THAT KATIA HAS TURNED TO THE NORTHEAST...THE VERTICAL SHEAR HAS DECREASED AND IT IS EXPECTED TO REMAIN LESS THAN 10 KT FOR THE NEXT 24 HOURS OR SO. THIS SHOULD ALLOW KATIA TO AT LEAST MAINTAIN ITS CURRENT INTENSITY...ESPECIALLY SINCE DOWNSTREAM BUOYS AHEAD OF THE CYCLONE ARE INDICATING SSTS OF 27-28C SOUTH OF 40N LATITUDE. BY 36 HOURS...EXTRATROPICAL TRANSITION IS EXPECTED...BUT KATIA IS STILL FORECAST TO HAVE HURRICANE-FORCE WINDS...WHICH WILL BE AIDED BY UNUSUALLY FAST FORWARD SPEEDS ABOVE 35 KT BEYOND 36 HOURS. ALTHOUGH KATIA IS FORECAST TO EVENTUALLY LOSE ITS TROPICAL CHARACTERISTICS...THIS CYCLONE IS EXPECTED TO REMAIN A VERY POWERFUL EXTRATROPICAL LOW PRESSURE SYSTEM THAT COULD BRING VERY STRONG WINDS TO THE BRITISH ISLES BY MONDAY. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 36.3N 68.8W 75 KT 85 MPH 12H 09/1200Z 38.1N 66.5W 75 KT 85 MPH 24H 10/0000Z 40.5N 61.1W 70 KT 80 MPH 36H 10/1200Z 42.9N 52.6W 70 KT 80 MPH...POST-TROP/EXTRATROP 48H 11/0000Z 46.4N 39.5W 65 KT 75 MPH...POST-TROP/EXTRATROP 72H 12/0000Z 54.1N 16.7W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 13/0000Z 61.0N 4.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 14/0000Z...ABSORBED $$ FORECASTER STEWART |
