ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM SUBTROPICAL STORM NADINE DISCUSSION NUMBER 42 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 500 PM AST FRI SEP 21 2012 NADINE HAS UNDERGONE AN INTERESTING TRANSFORMATION DURING THE PAST DAY OR SO. WHILE CONVECTION HAS WEAKENED OVERALL...A BAND OF MODERATE CONVECTION WRAPS AROUND THE EASTERN SEMICIRCLE OF THE STORM. AN UPPER-LEVEL LOW HAS ALSO DEVELOPED CLOSE TO THE CENTER OF NADINE...A RESULT OF ALL OF THE MID-LATITUDE TROUGH INTERACTIONS THAT THE CYCLONE HAS HAD RECENTLY. THE STORM HAS A LARGER-THAN- AVERAGE RADIUS OF MAXIMUM WINDS AND AN ASYMMETRIC WIND DISTRIBUTION. ALTHOUGH IT IS TEMPTING TO DECLARE NADINE POST-TROPICAL WITH THE DECAYING CONVECTION...THE CYCLONE APPEARS TO FIT MOST OF THE CHARACTERISTICS OF A SUBTROPICAL CYCLONE...ALBEIT FROM AN UNUSUAL WAY OF GETTING THERE. THE BEST ESTIMATE AT THIS TIME IS THAT NADINE HAS BECOME SUBTROPICAL...WHICH IS SUPPORTED BY A SUBTROPICAL CLASSIFICATION FROM TAFB. THE INITIAL WIND SPEED REMAINS 50 KT. NADINE IS MOVING TO THE SOUTH-SOUTHEAST AT ABOUT 10 KT. THE CYCLONE SHOULD GRADUALLY TURN TO THE SOUTHEAST AND EAST AS IT IS STEERED BY A TROUGH OVER THE FAR NORTHEASTERN ATLANTIC OCEAN. AFTER THE TROUGH MOVES AWAY...HOWEVER...VERY LITTLE MOTION IS EXPECTED IN A COUPLE DAYS TIME AS NADINE IS CAUGHT IN LIGHT STEERING CURRENTS. THE BULK OF THE GUIDANCE SUGGESTS THAT THE NEXT TROUGH IN ABOUT 5 DAYS WILL FINALLY CAUSE THE STORM TO MOVE A BIT FASTER TO THE NORTHEAST AND LOSE ANY REMAINING TROPICAL CHARACTERSTICS. THE NHC FORECAST IS CLOSE TO A BLEND OF THE GFS...GEFS...ECMWF...FIM...AND FLORIDA STATE SUPERENSEMBLES. THIS RESULTS IN A MORE SOUTHWARD TRACK EARLY ON...SMALL CHANGES IN THE MIDDLE OF THE FORECAST...AND AN EASTWARD ADJUSTMENT TO THE PREVIOUS FORECAST AT DAY 5. THE INTENSITY FORECAST IS VERY CHALLENGING AND IS OF LOW CONFIDENCE. VERY COLD UPPER-LEVEL TEMPERATURES APPEAR TO BE SUPPORTING THE CONVECTION NEAR THE CENTER IN COMBINATION WITH MARGINAL SSTS... ALTHOUGH THE WATERS SHOULD BE WARMING WITH TIME. MOST OF THE MODEL GUIDANCE SUGGESTS LITTLE CHANGE IN STRENGTH OR A SLIGHTLY WEAKER SYSTEM OVER THE NEXT COUPLE OF DAYS...AND THE OFFICIAL FORECAST IS NEAR THE MODEL CONSENSUS. IN A COUPLE OF DAYS...THE GFS AND ECMWF MODELS BUILD AN UPPER-LEVEL ANTICYCLONE NEAR NADINE...WHICH COULD FACILITATE A TRANSITION BACK TO A TROPICAL CYCLONE WHILE THE SYSTEM IS OVER MARGINAL SSTS. IT WOULD ALSO NOT BE SURPRISING IF IT DECAYED INTO A POST-TROPICAL CYCLONE AT ANY TIME. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 33.0N 27.0W 50 KT 60 MPH 12H 22/0600Z 31.6N 26.5W 45 KT 50 MPH 24H 22/1800Z 30.6N 25.8W 45 KT 50 MPH 36H 23/0600Z 30.5N 25.0W 45 KT 50 MPH 48H 23/1800Z 30.8N 24.7W 45 KT 50 MPH 72H 24/1800Z 31.7N 25.0W 50 KT 60 MPH 96H 25/1800Z 32.5N 24.5W 50 KT 60 MPH 120H 26/1800Z 32.5N 21.0W 50 KT 60 MPH...POST-TROPICAL $$ FORECASTER BLAKE NNNN
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Page last modified: Monday, 31-Dec-2012 12:09:44 UTC