000 WTNT42 KNHC 092042 TCDAT2 HURRICANE KATIA DISCUSSION NUMBER 47 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 500 PM AST FRI SEP 09 2011 DESPITE ITS HIGH LATITUDE LOCATION...KATIA HAS MAINTAINED A LARGE RAGGED EYE FEATURE IN BOTH CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY. THE INITIAL INTENSITY REMAINS 75 KT BASED ON CONSENSUS SATELLITE CURRENT INTENSITY ESTIMATES OF T4.5/77 KT FROM TAFB AND SAB...AND NHC AODT INTENSITY ESTIMATES. THE INITIAL MOTION ESTIMATE IS 060/33 KT. KATIA IS NOW EMBEDDED WITHIN DEEP-LAYER WEST-SOUTHWESTERLY FLOW AHEAD OF A SHARP MID-UPPER-LEVEL TROUGH AND ASSOCIATED COLD FRONT MOVING QUICKLY SOUTHEASTWARD ACROSS SOUTHEASTERN CANADA. THE LARGE HURRICANE IS EXPECTED TO CONTINUE TO ACCELERATE TOWARD THE EAST-NORTHEAST THROUGH THE REMAINDER OF THE FORECAST PERIOD. KATIA IS MOVING OVER COOLER WATER AND IN 18-24 HOURS AND IT IS EXPECTED TO BECOME A POWERFUL EXTRATROPICAL CYCLONE OVER THE FAR NORTH ATLANTIC. THE FORECAST TRACK IS DOWN THE MIDDLE OF THE TIGHTLY PACKED NHC MODEL GUIDANCE...AND LIES CLOSE TO THE CONSENSUS TRACK MODEL TVCN. KATIA WILL BE MOVING OVER WATER TEMPERATURES LESS THAN 22C BY 12 HOURS...AND THE CYCLONE COULD BECOME EXTRATROPICAL AT THAT TIME. HOWEVER...THE LARGE CIRCULATION IS EXPECTED TO TRANSPORT WARM UNSTABLE AIR SOUTH OF 40N LATITUDE NORTHWARD INTO THE EASTERN SEMICIRCLE...WHICH COULD HELP MAINTAIN CONVECTION A LITTLE LONGER THAN USUAL FOR SYSTEMS AT SUCH A HIGH LATITUDE. REGARDLESS... TRANSITION TO AN EXTRATROPICAL CYCLONE SHOULD BE COMPLETED BY 24 HOURS WHEN THE SYSTEM WILL HAVE MERGED WITH THE AFOREMENTIONED COLD FRONT AND BE OVER SSTS LESS THAN 20C. 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. INTERESTS IN AND AROUND THE BRITISH ISLES AND NORTHERN EUROPE SHOULD MONITOR PRODUCTS ISSUED BY THE UKMET OFFICE AT WWW.METOFFICE.GOV.UK/WEATHER/. NO 96-HOUR FORECAST POINT HAS BEEN PROVIDED DUE TO SOFTWARE ISSUES WHEN SYSTEMS MOVE EAST OF ZERO DEGREES LONGITUDE. FORECAST POSITIONS AND MAX WINDS INIT 09/2100Z 40.6N 62.7W 75 KT 85 MPH 12H 10/0600Z 42.6N 55.9W 70 KT 80 MPH 24H 10/1800Z 46.0N 44.9W 65 KT 75 MPH...POST-TROP/EXTRATROP 36H 11/0600Z 49.6N 33.3W 60 KT 70 MPH...POST-TROP/EXTRATROP 48H 11/1800Z 53.2N 22.9W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 12/1800Z 60.1N 4.6W 55 KT 65 MPH...POST-TROP/EXTRATROP 96H 13/1800Z...EAST OF ZERO DEGREES LONGITUDE $$ FORECASTER STEWART