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| #457064 (Received by flhurricane at: 4:48 AM 06.Sep.2011) TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 33 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 500 AM AST TUE SEP 06 2011 THE SATELLITE SIGNATURE OF KATIA HAS DECREASED SLIGHTLY IN ORGANIZATION DURING THE LAST SEVERAL HOURS...WITH THE CLOUD PATTERN BECOMING LESS SYMMETRIC AND THE EYE LESS DISTINCT AND COOLER. A TIMELY AMSU-B IMAGE FROM 0544 UTC INDICATED A DOUBLE EYEWALL STRUCTURE...SUGGESTING THAT KATIA IS AGAIN IN THE MIDST OF ANOTHER EYEWALL REPLACEMENT. SUBJECTIVE DVORAK INTENSITY ESTIMATES HAVE DECREASED SOMEWHAT SINCE 0000 UTC. A BLEND OF THESE AND THE LATEST ADT VALUES IS THE BASIS FOR THE CURRENT INTENSITY ESTIMATE OF 110 KT. DURING THE NEXT DAY OR SO...THE LARGE-SCALE ATMOSPHERIC AND OCEANIC ENVIRONMENT ARE LIKELY TO REMAIN CONDUCIVE FOR KATIA TO MAINTAIN MAJOR HURRICANE STATUS. HOWEVER...FLUCTUATIONS IN STRENGTH DUE TO A DIFFICULT-TO-FORECAST INNER CORE EVOLUTION ARE PROBABLE DURING THIS TIME. AFTER 48 HOURS...THE HURRICANE WILL BE ENCOUNTERING AN ENVIRONMENT OF GRADUALLY INCREASING VERTICAL SHEAR AND LOWER OCEANIC HEAT CONTENT...AND WEAKENING SHOULD COMMENCE. LATER IN THE FORECAST PERIOD...KATIA SHOULD MOVING NEARLY PARALLEL TO A STRONG GRADIENT OF SEA SURFACE TEMPERATURE AND WILL BECOME EMBEDDED IN AN INCREASINGLY BAROCLINIC ENVIRONMENT AS IT NEARS A MID-LATITUDE JET...BOTH OF WHICH SHOULD PROMOTE ITS TRANSITION TO AN EXTRATROPICAL CYCLONE. THE OFFICIAL NHC INTENSITY FORECAST IS CLOSE TO THE PREVIOUS ONE AND SHOWS KATIA AS STRONG CYCLONE THROUGH EXTRATROPICAL TRANSITION. KATIA APPEARS TO BE EXHIBITING A TROCHOIDAL MOTION...WITH A SMOOTHING OF RECENT FIXES YIELDING AN INITIAL MOTION ESTIMATE OF 315/9. VERY LITTLE CHANGE HAS BEEN MADE TO THE NHC FORECAST TRACK ON THIS PACKAGE. GLOBAL MODELS SHOW KATIA BEING STEERED AROUND THE SOUTHWEST SIDE OF A MID-LEVEL RIDGE EAST OF BERMUDA AND TOWARD A INTO A WEAKNESS OVER THE WESTERN ATLANTIC DURING THE NEXT COUPLE OF DAYS. BY 48 HOURS...KATIA SHOULD TURN NORTHWARD ROUGHLY ALONG 70W IN BETWEEN A LARGE CUT-OFF LOW OVER THE EASTERN UNITED STATES AND THE RIDGE TO THE EAST. THE HURRICANE SHOULD THEN ACCELERATE NORTHEASTWARD AND THEN EAST-NORTHEASTWARD AS IT BECOMES EMBEDDED IN A FAST AND NEARLY ZONAL FLOW ON THE SOUTH SIDE OF A BROAD TROUGH COVERING THE FAR NORTH ATLANTIC. THE NEW NHC TRACK FORECAST IS DOWN THE CENTER OF THE GUIDANCE ENVELOPE THROUGH 72 HOURS AND A BIT TO THE EAST OF THE MULTI-MODEL CONSENSUS AT LATER TIMES. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 26.5N 65.1W 110 KT 125 MPH 12H 06/1800Z 27.4N 66.2W 115 KT 135 MPH 24H 07/0600Z 28.6N 67.6W 110 KT 125 MPH 36H 07/1800Z 30.2N 69.0W 105 KT 120 MPH 48H 08/0600Z 32.0N 69.8W 90 KT 105 MPH 72H 09/0600Z 36.2N 68.5W 80 KT 90 MPH 96H 10/0600Z 40.0N 60.0W 75 KT 85 MPH 120H 11/0600Z 44.0N 41.5W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ FORECASTER KIMBERLAIN |
