000 WTNT42 KNHC 072051 TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 39 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 500 PM AST WED SEP 07 2011 THE CLOUD TOPS ASSOCIATED WITH KATIA WARMED DURING THE EARLY AFTERNOON...BUT SINCE THAT TIME A NEW BURST OF DEEP CONVECTION HAS FORMED TO THE NORTHEAST OF THE CENTER. AN EARLIER TRMM PASS ONCE AGAIN SHOWED A SMALL REMNANT OF THE INNER EYEWALL WITH A LARGE BAND OF CONVECTION OVER THE NORTH AND EAST SEMICIRCLES OF THE CIRCULATION. SUBJECTIVE AND OBJECTIVE DVORAK T- AND CI-NUMBERS CONTINUE TO SLOWLY DECREASE...THEREFORE THE INITIAL INTENSITY IS LOWERED TO 70 KT. THERE HAS BEEN LITTLE CHANGE TO THE INTENSITY FORECAST REASONING. MODERATE WESTERLY SHEAR CURRENTLY OVER THE SYSTEM IS FORECAST TO DECREASE ON THURSDAY...HOWEVER THIS IS LIKELY TO BE NEGATED BY SLIGHTLY COOLER SSTS THAT THE HURRICANE WILL BE MOVING OVER. OVERALL...LITTLE CHANGE IN STRENGTH IS FORECAST DURING THE NEXT COUPLE OF DAYS. KATIA IS EXPECTED TO BECOME A LARGE AND POWERFUL EXTRATROPICAL CYCLONE IN ABOUT 72 HOURS. THE INITIAL MOTION ESTIMATE IS 320/9. THE MODELS REMAIN IN VERY GOOD AGREEMENT MOVING KATIA AROUND THE WEST SIDE OF A MID/UPPER-LEVEL RIDGE OVER THE CENTRAL ATLANTIC DURING THE NEXT 24-36 HOURS. AFTER 48 HOURS...THE CYCLONE IS EXPECTED TO ACCELERATE NORTHEASTWARD AHEAD OF A BROAD TROUGH MOVING ACROSS THE CANADIAN MARITIMES. THE GFS AND ECMWF MODELS ARE STILL IN REMARKABLY GOOD AGREEMENT ON THE EXTRATROPICAL PORTION OF THE TRACK. THE OFFICIAL FORECAST HAS BEEN NUDGED NORTHWARD AT 36 HOURS AND BEYOND AND IS NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 29.9N 69.7W 70 KT 80 MPH 12H 08/0600Z 31.3N 70.1W 70 KT 80 MPH 24H 08/1800Z 33.8N 70.0W 70 KT 80 MPH 36H 09/0600Z 36.6N 68.5W 70 KT 80 MPH 48H 09/1800Z 39.2N 64.5W 70 KT 80 MPH 72H 10/1800Z 44.5N 46.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 96H 11/1800Z 53.0N 26.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 12/1800Z 60.0N 7.0W 60 KT 70 MPH...POST-TROP/EXTRATROP $$ FORECASTER BROWN