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| #457358 (Received by flhurricane at: 4:50 AM 07.Sep.2011) TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 37 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 500 AM AST WED SEP 07 2011 THE CLOUD PATTERN OF KATIA HAS BECOME A LITTLE LESS ORGANIZED OVERNIGHT. CLOUD TOP TEMPERATURES HAVE GENERALLY BEEN WARMING AND DRY AIR APPEARS TO WRAPPING AROUND THE WESTERN SEMICIRCLE OF THE CIRCULATION...THE LATTER GIVING THE CYCLONE A SOMEWHAT HOLLOW APPEARANCE. IN ADDITION...THERE APPEARS TO BE NORTHWESTERLY SHEAR OVER THE HURRICANE...AS EVIDENCED BY CIRRUS CLOUD MOTIONS AND CONFIRMED BY UW-CIMSS ANALYSES. DVORAK T- AND CI-NUMBERS FROM TAFB AND SAB ARE LOWER...AND A REASONABLE BLEND OF THESE DATA GIVES AN INTENSITY ESTIMATE OF 80 KT. AN EYEWALL REPLACEMENT CYCLE THAT BEGAN 24-36 HOURS APPEARS TO HAVE BEEN INTERRUPTED...WITH EARLIER MICROWAVE IMAGERY SHOWING AN OUTER EYEWALL AT LARGE RADIUS THAT WAS NOT CONTRACTING MUCH. THIS STRUCTURE...ALONG WITH THE MODERATE SHEAR...SUGGESTS NOT MUCH CHANGE IN STRENGTH...FOLLOWED BY ONLY A SLOW WEAKENING DURING THE NEXT FEW DAYS AS KATIA REMAINS OVER RELATIVELY WARM WATERS. AFTER 72 HOURS...KATIA WILL QUICKLY MOVE ALONG A STRONG GRADIENT OF SSTS AND ENCOUNTER AN INCREASINGLY BAROCLINIC ENVIRONMENT...BOTH OF WHICH SHOULD RESULT IN A RAPID TRANSITION TO AN INTENSE EXTRATROPICAL CYCLONE. POST-TROPICAL CYCLONE KATIA IS EXPECTED TO BE A SIGNIFICANT WEATHER SYSTEM OVER THE FAR NORTH ATLANTIC FOR AT LEAST A COUPLE OF DAYS. THE OFFICIAL NHC WIND SPEED FORECAST IS LOWERED IN ACCORDANCE WITH THE LATEST INTENSITY GUIDANCE AND IS IN BEST AGREEMENT WITH THE MODEL CONSENSUS. THE INITIAL MOTION IS A FAIRLY SLOW 315/08. GLOBAL MODELS SHOW KATIA GRADUALLY TURNING FROM NORTHWESTWARD TO NORTHWARD INTO A WEAKNESS IN THE SUBTROPICAL RIDGE OVER THE WESTERN ATLANTIC DURING THE NEXT 24-36 HOURS. AFTER THAT...THE HURRICANE IS EXPECTED TO GRADUALLY RECURVE INTO THE WESTERLIES AND ACCELERATE NORTHEASTWARD ON THE SOUTH SIDE OF A BROAD TROUGH COVERING THE FAR NORTH ATLANTIC. THE TRACK GUIDANCE HAS CONSISTENTLY BEEN HANDLING THE STEERING FLOW AROUND THE STORM WELL FOR SEVERAL FORECAST CYCLES AND IS TIGHTLY CLUSTERED...GIVING HIGH CONFIDENCE TO THE FORECAST. ONLY MINOR CHANGES WERE MADE TO THE PREVIOUS FORECAST TRACK...WITH THE CURRENT NHC TRACK AGAIN CLOSE TO THE MULTI-MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 28.7N 67.9W 80 KT 90 MPH 12H 07/1800Z 29.8N 69.0W 80 KT 90 MPH 24H 08/0600Z 31.7N 69.6W 75 KT 85 MPH 36H 08/1800Z 34.0N 69.5W 75 KT 85 MPH 48H 09/0600Z 36.4N 67.9W 70 KT 80 MPH 72H 10/0600Z 40.9N 58.2W 65 KT 75 MPH 96H 11/0600Z 47.0N 38.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 12/0600Z 59.0N 17.5W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ FORECASTER KIMBERLAIN/PASCH |
