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| #544625 (Received by flhurricane at: 10:53 AM 21.Sep.2012) TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 41 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 1100 AM AST FRI SEP 21 2012 NADINE REMAINS A MARGINAL TROPICAL CYCLONE. MODEL ANALYSES AND PHASE SPACE DIAGRAMS SUGGEST THAT THE CYCLONE REMAINS WARM CORE...WHILE SURFACE DATA AND SATELLITE IMAGERY INDICATE THAT THE CENTER OF NADINE IS SOUTH OF THE FRONTAL BOUNDARY DRAPED ACROSS THE AZORES. HOWEVER...THE CONVECTIVE PATTERN HAS DEGRADED SIGNIFICANTLY OVER THE PAST FEW HOURS...WITH ONLY A RAGGED BAND OF WARMING CLOUD TOPS REMAINING SOUTH AND EAST OF THE CENTER. THE DECREASE IN CONVECTION IS LIKELY DUE TO A COMBINATION OF MARGINAL SSTS AND DRY AIR THAT HAS WORKED ITS WAY INTO THE INNER PART OF THE CIRCULATION. A 1224 UTC ASCAT PASS SHOWED SOME 40 TO 45 KT WINDS NORTHWEST OF THE CENTER...AND THE INITIAL INTENSITY IS CONSERVATIVELY LOWERED TO 50 KT FOR THIS ADVISORY. TRANSITION TO POST-TROPICAL STATUS IS EXPECTED SOON...POSSIBLY BY LATER TODAY IF ORGANIZED DEEP CONVECTION DOES NOT RETURN. AFTER TRANSITION...ONLY SLIGHT WEAKENING IS FORECAST. NADINE MOVED A LITTLE WEST OF DUE SOUTH EARLIER THIS MORNING... LIKELY DUE TO THE DEEP-LAYER FLOW BETWEEN A MID-LEVEL RIDGE TO THE NORTHWEST AND A MID/UPPER-LEVEL LOW TO THE NORTHEAST. HOWEVER...NADINE HAS TURNED SOUTHWARD RECENTLY...AND THE INITIAL MOTION ESTIMATE IS 180/09. AS THE UPPER LOW BEGINS TO LIFT OUT TO THE EAST...NADINE SHOULD TURN SOUTHEASTWARD OVER THE NEXT 12 TO 24 HOURS. AFTERWARD NADINE WILL AGAIN BE CAUGHT IN WEAK STEERING CURRENTS...AND THE OFFICIAL FORECAST SHOWS A SLOW EASTWARD TO NORTHEASTWARD MOTION AT DAYS 2 THROUGH 5. THIS FOLLOWS THE GENERAL TREND SEEN IN MOST OF THE GUIDANCE...BUT AT A MUCH SLOWER FORWARD SPEED DUE TO THE LARGE SPREAD IN THE MODELS LATE IN THE PERIOD. THIS UNCERTAINTY STEMS FROM LARGE RUN-TO-RUN AND MODEL-TO-MODEL VARIABILITY IN THE DETAILS ABOUT HOW MUCH NADINE WILL INTERACT WITH ANOTHER TROUGH DEEPENING OVER THE NORTHEASTERN ATLANTIC LATE IN THE PERIOD. DUE TO THE RECENT SOUTHWARD JOG OF NADINE...THE OFFICIAL FORECAST HAS BEEN SHIFTED ABOUT 60 TO 70 NAUTICAL MILES TO THE WEST AND SOUTH OF THE PREVIOUS ONE. THE 34-KT WIND RADII WERE EXPANDED IN THE WESTERN SEMICIRCLE BASED ON THE ABOVE-MENTIONED ASCAT PASS. FORECAST POSITIONS AND MAX WINDS INIT 21/1500Z 34.1N 27.5W 50 KT 60 MPH 12H 22/0000Z 32.9N 26.9W 50 KT 60 MPH 24H 22/1200Z 31.8N 25.8W 50 KT 60 MPH...POST-TROPICAL 36H 23/0000Z 31.4N 25.1W 50 KT 60 MPH...POST-TROPICAL 48H 23/1200Z 31.4N 24.4W 50 KT 60 MPH...POST-TROPICAL 72H 24/1200Z 31.6N 24.0W 45 KT 50 MPH...POST-TROPICAL 96H 25/1200Z 32.0N 23.5W 45 KT 50 MPH...POST-TROPICAL 120H 26/1200Z 32.5N 22.5W 45 KT 50 MPH...POST-TROPICAL $$ FORECASTER BRENNAN |
