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#457284 (Received by flhurricane at: 10:38 PM 06.Sep.2011) TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 36 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 1100 PM AST TUE SEP 06 2011 SINCE THE AIRCRAFT DEPARTED KATIA THIS AFTERNOON THE SATELLITE PRESENTATION HAS IMPROVED SLIGHTLY. ALTHOUGH THE CONVECTIVE PATTERN HAS GAINED CURVATURE...THUNDERSTORM ACTIVITY IS QUITE THIN OVER THE WESTERN SEMICIRCLE...AS SEEN IN THE LAST FEW MICROWAVE OVERPASSES. THIS ASYMMETRIC PATTERN IS LIKELY DUE TO SOME WESTERLY SHEAR AND DRY AIR ENTRAINMENT. THE INITIAL WIND SPEED IS HELD AT 90 KT FOR THIS ADVISORY...WHICH IS IN AGREEMENT WITH AN AVERAGE OF THE DVORAK T AND CI NUMBERS. KATIA IS STILL MOVING NORTHWESTWARD AT ABOUT 8 KT...BUT IS EXPECTED TO TURN TOWARD THE NORTH WITH AN INCREASE IN FORWARD SPEED DURING THE NEXT 24 TO 36 HOURS AS THE HURRICANE BECOMES EMBEDDED IN THE FLOW BETWEEN THE SUBTROPICAL RIDGE AND A LARGE UPPER-LEVEL CUTOFF LOW OVER THE OHIO VALLEY OF THE UNITED STATES. KATIA IS EXPECTED TO ACCELERATE TO THE NORTHEAST AND EAST-NORTHEAST IN TWO TO THREE DAYS AS THE CYCLONE GETS SWEPT UP IN THE STRONG MID-LATITUDE FLOW. THE MODELS REMAIN IN GOOD AGREEMENT ON THE FUTURE TRACK OF KATIA...AND THE OFFICIAL FORECAST IS SIMILAR TO THE PREVIOUS ONE. THE 96- AND 120-HOUR FORECAST POINTS ARE LARGELY BASED ON GUIDANCE FROM THE OCEAN PREDICTION CENTER. LITTLE CHANGE IN STRENGTH OR GRADUAL WEAKENING IS LIKELY DURING THE NEXT 24 TO 48 HOURS. BEYOND THAT TIME...KATIA WILL BE MOVING OVER COOLER WATERS AND IS EXPECTED TO ENCOUNTER STRONGER SOUTHWESTERLY SHEAR. THESE FACTORS SHOULD LEAD TO EXTRATROPICAL TRANSITION... WHICH IS LIKELY TO OCCUR IN THREE TO FOUR DAYS. ALL OF THE GLOBAL MODELS SHOW KATIA BECOMING A LARGE AND POWERFUL POST-TROPICAL CYCLONE OVER THE NORTH ATLANTIC. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 28.1N 67.2W 90 KT 105 MPH 12H 07/1200Z 29.0N 68.3W 85 KT 100 MPH 24H 08/0000Z 30.6N 69.5W 85 KT 100 MPH 36H 08/1200Z 32.7N 69.9W 80 KT 90 MPH 48H 09/0000Z 35.2N 69.2W 80 KT 90 MPH 72H 10/0000Z 40.0N 62.5W 75 KT 85 MPH 96H 11/0000Z 45.0N 44.0W 70 KT 80 MPH...POST-TROP/EXTRATROP 120H 12/0000Z 55.0N 25.0W 70 KT 80 MPH...POST-TROP/EXTRATROP $$ FORECASTER CANGIALOSI/BRENNAN |