000 WTNT42 KNHC 101456 TCDAT2 POST-TROPICAL CYCLONE KATIA DISCUSSION NUMBER 50 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122011 1100 AM AST SAT SEP 10 2011 KATIA HAS LOST ITS TROPICAL CHARACTERISTICS...BUT IT STILL REMAINS A POWERFUL POST-TROPICAL CYCLONE. THE CENTER OF KATIA PASSED JUST NORTH OF CANADIAN BUOY 44140 AROUND 11Z...AND THE BUOY REPORTED A PRESSURE OF 957 MB WITH 31 KT WINDS. BASED ON THAT INFORMATION... THE CENTRAL PRESSURE OF KATIA IS ESTIMATED TO BE 954 MB. AT 12Z...THE SAME BUOY REPORTED A SUSTAINED WIND OF 62 KT IN THE NORTHWESTERN QUADRANT. ALL OF THIS INFORMATION JUSTIFIES KEEPING THE INTENSITY AT 70 KT. THE INITIAL MOTION IS NOW A VERY BRISK 060/46 KT. KATIA IS EMBEDDED IN DEEP-LAYER WEST-SOUTHWESTERLY FLOW AHEAD OF A STRONG SHORTWAVE TROUGH DIGGING SOUTHEASTWARD ACROSS THE CANADIAN MARITIMES REGION. POWERFUL POST-TROPICAL CYCLONE KATIA IS FORECAST TO CONTINUE TO MOVE RAPIDLY TO THE EAST-NORTHEAST OR NORTHEAST THROUGH THE REMAINDER OF THE FORECAST PERIOD...AND MOVE OVER OR NEAR THE NORTHWESTERN BRITISH ISLES ON MONDAY. THE TIGHTLY PACKED NHC MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON THIS SCENARIO...AND THE OFFICIAL TRACK FORECAST IS A BLEND OF THE MULTI-MODEL CONSENSUS... TVCN...AND GUIDANCE PROVIDED BY THE NOAA OCEAN PREDICTION CENTER. KATIA HAS LOST MUCH OF ITS DEEP CONVECTION NEAR THE CENTER. ALTHOUGH THE CENTRAL PRESSURE HAS DECREASED BY AT LEAST 10 MB OVER THE PAST 24 HOURS...THESE PRESSURE FALLS ARE ATTRIBUTED TO THE INCREASE IN BAROCLINIC ENERGY ACROSS THE SYSTEM AND NOT DUE TO CONVECTIVE FEEDBACK. SURFACE OBSERVATIONS INDICATE KATIA HAS MERGED WITH A FRONTAL SYSTEM...AND THE CONTRAST BETWEEN THE VERY WARM AND MOIST AIR TO THE SOUTH AND COLDER AIR TO THE NORTH OF THE FRONTAL BOUNDARY SHOULD ACT TO KEEP KATIA AS A STRONG POST-TROPICAL CYCLONE UNTIL IT REACHES THE BRITISH ISLES ON MONDAY. THE INTENSITY FORECAST IS A BLEND OF NHC INTENSITY FORECAST GUIDANCE AND INPUT FROM THE NOAA OCEAN PREDICTION CENTER. CURRENT WIND RADII WERE ADJUSTED BASED ON RECENT BUOY REPORTS...AND FORECAST WIND RADII WERE PROVIDED BY THE OCEAN PREDICTION CENTER. NO 96-HOUR FORECAST POINT HAS BEEN PROVIDED DUE TO SOFTWARE ISSUES WHEN SYSTEMS MOVE EAST OF ZERO DEGREES LONGITUDE. ALTHOUGH THIS IS THE FINAL ADVISORY ISSUED ON KATIA BY THE NATIONAL HURRICANE CENTER...INTERESTS IN AND AROUND THE BRITISH ISLES AND NORTHERN EUROPE SHOULD CLOSELY MONITOR FUTURE PRODUCTS ISSUED BY THE UK MET OFFICE AT WWW.METOFFICE.GOV.UK/WEATHER. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 44.7N 47.7W 70 KT 80 MPH...POST-TROP/EXTRATROP 12H 11/0000Z 47.5N 38.5W 70 KT 80 MPH...POST-TROP/EXTRATROP 24H 11/1200Z 51.5N 27.5W 65 KT 75 MPH...POST-TROP/EXTRATROP 36H 12/0000Z 54.5N 19.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 48H 12/1200Z 57.5N 11.5W 60 KT 70 MPH...POST-TROP/EXTRATROP 72H 13/1200Z 61.0N 1.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 14/1200Z...EAST OF ZERO DEGREES LONGITUDE $$ FORECASTER STEWART