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| #457222 (Received by flhurricane at: 4:48 PM 06.Sep.2011) TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 35 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 500 PM AST TUE SEP 06 2011 A 1509 UTC TRMM PASS INDICATES THAT THE INNER EYEWALL OF KATIA IS DECAYING WITHIN A LARGER EYEWALL...SUGGESTING THAT THE HURRICANE IS NEARING THE END OF ITS EYEWALL REPLACEMENT. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT MADE TWO PASSES THROUGH THE STORM AND MEASURED A MAXIMUM 700-MB FLIGHT-LEVEL WIND OF 114 KT AND A PEAK SURFACE WIND OF 81 KT FROM THE SFMR. THE PLANE ALSO REPORTED THAT THE NEW RADIUS OF MAXIMUM WINDS IS ABOUT 55 N MI...AND THE 64- AND 50-KT RADII HAVE EXPANDED. BASED ON THE EXPANSION OF THE WIND FIELD...IT IS ASSUMED THAT THE STANDARD FLIGHT-LEVEL TO SURFACE WIND RELATIONSHIP MAY BE TOO HIGH...AND THE INITIAL INTENSITY IS THEREFORE SET AT 90 KT. KATIA CONTINUES TO MOVE ON TRACK WITH A MOTION OF 310/9 KT. THE HURRICANE WILL BE MOVING AROUND THE SOUTHWESTERN PERIPHERY OF A CENTRAL ATLANTIC MID-LEVEL HIGH IN THE SHORT-TERM...AND IT SHOULD BEGIN TO TURN TOWARD THE NORTH-NORTHWEST AND NORTH OVER THE NEXT 48 HOURS. AFTER 48 HOURS...THE MODEL GUIDANCE CONTINUES TO TREND TOWARD A DELAY IN PICKING UP THE HURRICANE BY THE FAST MID-LATITUDE WESTERLIES...AND THIS HAS RESULTED IN ANOTHER SLIGHT NORTHWESTWARD SHIFT OF THE GUIDANCE ENVELOPE AT 72 HOURS. THE OFFICIAL FORECAST HAS ALSO BEEN NUDGED IN THAT DIRECTION...ENDING UP ON THE SOUTHEASTERN SIDE OF THE GUIDANCE. THE MODEL SPREAD APPEARS TO BE DECREASING AT THE 96- AND 120-HOUR POINTS AS ALL THE MODELS HAVE KATIA ACCELERATING IN THE WESTERLIES...AND LITTLE CHANGE TO THE OFFICIAL FORECAST WAS REQUIRED AT THOSE TIMES. THE EXPANDING WIND FIELD OF KATIA SUGGESTS THAT LITTLE CHANGE IN INTENSITY SHOULD OCCUR OVER THE NEXT DAY OR SO. THE HURRICANE COULD BE AFFECTED BY SOME SHEAR OVER THE NEXT FEW DAYS...AND IT IS ALREADY MOVING OVER WATERS THAT ARE BECOMING GRADUALLY LESS CONDUCIVE FOR RE-STRENGTHENING. GRADUAL WEAKENING IS INDICATED IN THE OFFICIAL FORECAST FROM 24 TO 72 HOURS. THEREAFTER...THE VARIOUS GLOBAL MODEL FIELDS ARE IN AGREEMENT SHOWING KATIA BECOMING ENTANGLED WITHIN A FRONTAL ZONE BY 96 HOURS. THE CYCLONE IS THEREFORE FORECAST TO BE EXTRATROPICAL AT THAT TIME...BUT THERE SHOULD BE ENOUGH BAROCLINIC FORCING TO MAINTAIN IT AS A POWERFUL HURRICANE-FORCE LOW PRESSURE SYSTEM. THE OFFICIAL FORECAST AT THE END OF THE FORECAST PERIOD IS BASED ON GUIDANCE FROM THE OCEAN PREDICTION CENTER. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 27.6N 66.7W 90 KT 105 MPH 12H 07/0600Z 28.5N 67.8W 90 KT 105 MPH 24H 07/1800Z 29.9N 69.2W 90 KT 105 MPH 36H 08/0600Z 31.7N 70.0W 85 KT 100 MPH 48H 08/1800Z 34.0N 69.9W 85 KT 100 MPH 72H 09/1800Z 39.0N 66.0W 75 KT 85 MPH 96H 10/1800Z 44.0N 50.0W 70 KT 80 MPH...POST-TROP/EXTRATROP 120H 11/1800Z 53.0N 29.0W 70 KT 80 MPH...POST-TROP/EXTRATROP $$ FORECASTER BERG/BRENNAN |
