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| #544772 (Received by flhurricane at: 10:38 PM 21.Sep.2012) TCDAT4 POST-TROPICAL CYCLONE NADINE DISCUSSION NUMBER 43 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 1100 PM AST FRI SEP 21 2012 WHILE NADINE CONTINUES TO MAINTAIN A WARM CORE AND A VIGOROUS LOW-LEVEL CIRCULATION...THERE HAS BEEN NO SIGNIFICANT CONVECTION ASSOCIATED WITH THE SYSTEM FOR THE PAST 15 HOURS OR SO. WHAT CONVECTION THAT CURRENTLY REMAINS IS IN POORLY-DEFINED BANDS TO THE SOUTHWEST OF THE CENTER. BASED ON THIS...THE SYSTEM DOES NOT REALLY FIT THE DEFINITION OF A SUBTROPICAL CYCLONE AND SO IT IS DECLARED TO BE POST-TROPICAL. THE INITIAL INTENSITY IS HELD AT 50 KT DUE TO A LACK OF DATA NEAR THE CENTER...BUT THIS COULD BE A LITTLE GENEROUS. THE INITIAL MOTION IS 165/11. NADINE IS CURRENTLY BEING STEERED BY A DEEP-LAYER TROUGH TO ITS NORTHEAST. A GENERALLY SOUTHEASTWARD MOTION WITH A DECREASE IN FORWARD SPEED IS EXPECTED DURING THE NEXT 24 HOURS. AFTER THAT...THERE ARE TWO FUTURE TRACK SCENARIOS FOR NADINE OR ITS REMNANTS. THE FIRST IS THAT ENOUGH TROUGHING REMAINS NORTHEAST OF THE CYCLONE TO STEER IT GENERALLY EASTWARD. THIS SCENARIO IS SUPPORTED BY THE ECMWF...UKMET...GFDL...AND FLORIDA STATE SUPERENSEMBLE. THE SECOND IS THAT DEEP-LAYER RIDGING DEVELOPS NORTH OF THE CYCLONE AND STEERS IT IN A GENERALLY WEST- NORTHWESTWARD DIRECTION. THIS SCENARIO IS SUPPORTED BY THE GFS... GFS ENSEMBLE MEAN...NOGAPS...AND CANADIAN MODELS. IT SHOULD BE NOTED THAT THE VARIOUS ENSEMBLE MEMBERS OF THE ECMWF...GFS... UKMET...AND CANADIAN MODELS ARE SPLIT BETWEEN THESE TWO SCENARIOS... MAKING IT DIFFICULT TO TELL WHICH WILL COME TO PASS. THE NEW TRACK FORECAST WILL FOLLOW THE EASTWARD SCENARIO FROM THE PREVIOUS FORECAST...WITH A SLOW FORWARD MOTION DUE TO THE VERY LARGE SPREAD IN THE GUIDANCE AFTER 24 HOURS. THIS MAY NOT BE THE LAST HURRAH FOR NADINE. THE CYCLONE IS MOVING TOWARD WARMER SEA SURFACE TEMPERATURES...AND SEVERAL OF THE GLOBAL MODELS SHOW A FAVORABLE UPPER-LEVEL WIND PATTERN DEVELOPING OVER THE SYSTEM IN 48-72 HOURS. THE SHIPS AND LGEM MODELS FORECAST THE SYSTEM TO STRENGTHEN AND RE-ACQUIRE TROPICAL CYCLONE CHARACTERISTICS BY THAT TIME. THE INTENSITY FORECAST WILL NOT SHOW A TRANSITION BACK TO A TROPICAL CYCLONE...BUT IT IS A DISTINCT POSSIBILITY...ESPECIALLY IF THE SYSTEM TURNS WESTWARD UNDER THE RIDGE. EVEN IF THIS TRANSITION DOES NOT OCCUR...THE MAJORITY OF THE DYNAMICAL MODELS MAINTAIN NADINE AS A VIGOROUS CYCLONE THROUGH THE FORECAST PERIOD...AND THE INTENSITY FORECAST IS THUS CHANGED LITTLE FROM THE PREVIOUS FORECAST. THIS WILL BY THE LAST ADVISORY ON NADINE BY THE NATIONAL HURRICANE CENTER UNLESS REGENERATION OCCURS. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 31.9N 26.6W 50 KT 60 MPH...POST-TROPICAL 12H 22/1200Z 31.0N 26.1W 45 KT 50 MPH...POST-TROPICAL 24H 23/0000Z 30.5N 25.2W 45 KT 50 MPH...POST-TROPICAL 36H 23/1200Z 30.7N 24.5W 45 KT 50 MPH...POST-TROPICAL 48H 24/0000Z 31.4N 24.5W 45 KT 50 MPH...POST-TROPICAL 72H 25/0000Z 32.5N 24.5W 50 KT 60 MPH...POST-TROPICAL 96H 26/0000Z 32.5N 23.0W 55 KT 65 MPH...POST-TROPICAL 120H 27/0000Z 33.0N 20.0W 50 KT 60 MPH...POST-TROPICAL $$ FORECASTER BEVEN |
