000 WTNT42 KNHC 091436 TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 46 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 1100 AM AST FRI SEP 09 2011 KATIA HAS MAINTAINED A RAGGED EYE FEATURE IN BOTH CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY DURING THE PAST 6 HOURS...SO THE INTENSITY WILL REMAIN AT 75 KT...WHICH IS CONSISTENT WITH NHC AODT AND SAB INTENSITY ESTIMATES. DESPITE THE HIGH LATITUDE OF THE CYCLONE...KATIA CONTINUES TO HAVE A WELL-DEFINED UPPER-LEVEL OUTFLOW PATTERN. THE INITIAL MOTION ESTIMATE IS 050/25 KT. KATIA IS WELL NORTH OF THE SUBTROPICAL RIDGE AXIS ORIENTED ALONG 33N LATITUDE...AND WATER VAPOR IMAGERY INDICATES THAT THE CYCLONE IS NOW ENTERING THE FAST WESTERLY FLOW REGIME THAT LIES NORTH OF 40N LATITUDE. AS A RESULT...KATIA IS EXPECTED TO ACCELERATE NORTHEASTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD. THE HURRICANE SHOULD PASS OVER MUCH COLDER WATER BY 24 HOURS AND BECOME A POWERFUL EXTRATROPICAL CYCLONE. THE FORECAST TRACK IS DOWN THE MIDDLE OF THE TIGHTLY PACKED MODEL GUIDANCE...AND LIES CLOSE TO THE NHC CONSENSUS MODEL TVCN. KATIA WILL BE MOVING OVER WATER TEMPERATURES LESS THAN 26C BY 12 HOURS...AND OVER SSTS LESS THAN 20C BY 24 HOURS. THEREFORE...A FAIRLY QUICK TRANSITION TO AN EXTRATROPICAL CYCLONE IS EXPECTED BY 24 HOURS WHEN THE SYSTEM WILL ALSO BE MERGING WITH AN APPROACHING FRONTAL ZONE. ALTHOUGH KATIA IS FORECAST TO WEAKEN BELOW HURRICANE FORCE BY 36 HOURS...THE LARGE EXTRATROPICAL LOW PRESSURE SYSTEM IS EXPECTED TO CONTAIN STORM-FORCE WINDS WHEN IT APPROACHES THE BRITISH ISLES IN 3 DAYS. NO 96-HOUR FORECAST POINT HAS BEEN PROVIDED DUE TO COMPUTATIONAL ISSUES WHEN SYSTEMS MOVE EAST OF ZERO DEGREES LONGITUDE. FORECAST POSITIONS AND MAX WINDS INIT 09/1500Z 39.3N 65.8W 75 KT 85 MPH 12H 10/0000Z 41.1N 60.4W 70 KT 80 MPH 24H 10/1200Z 44.1N 49.9W 65 KT 75 MPH...POST-TROP/EXTRATROP 36H 11/0000Z 47.8N 37.8W 60 KT 70 MPH...POST-TROP/EXTRATROP 48H 11/1200Z 51.5N 26.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 12/1200Z 58.5N 7.5W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 13/1200Z...EAST OF ZERO DEGREES LONGITUDE $$ FORECASTER STEWART