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#544010 (Received by flhurricane at: 10:41 PM 18.Sep.2012) TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 31 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 1100 PM AST TUE SEP 18 2012 THE CONVECTION NEAR THE CENTER OF NADINE HAS DISSIPATED THIS EVENING AND THE CYCLONE NOW HAS ONE RAGGED BAND OF CONVECTION OVER THE NORTHERN PORTION OF THE CIRCULATION. DVORAK DATA T-NUMBERS HAVE DECREASED AND A BLEND OF THE FINAL T- AND CI-NUMBERS YIELDS AN INITIAL INTENSITY OF 45 KT. NADINE IS CURRENTLY OVER SSTS OF AROUND 25 DEGREES CELSIUS AND IT SHOULD MOVE OVER SLIGHTLY COOLER WATERS DURING THE NEXT COUPLE OF DAYS. THE PREDICTED SLOW MOTION OF NADINE COULD ALSO CAUSE SOME UPWELLING...WHICH IS LIKELY TO REDUCE THE SSTS A LITTLE MORE. ONE WOULD EXPECT THE COOL WATER AND MODERATE SOUTHWESTERLY SHEAR TO CAUSE NADINE TO WEAKEN. HOWEVER...MUCH OF THE INTENSITY GUIDANCE SHOWS LITTLE CHANGE IN STRENGTH DURING THE NEXT COUPLE OF DAYS. THE GLOBAL MODELS ACTUALLY PREDICT SOME INCREASE IN WINDS OVER THE NORTHWESTERN PORTION OF THE CYCLONE AS A LARGE HIGH PRESSURE SYSTEM BUILDS SOUTHEASTWARD DURING THE NEXT COUPLE OF DAYS. AS A RESULT...THE NHC FORECAST CALLS FOR LITTLE CHANGE IN INTENSITY FOR MOST OF THE FORECAST PERIOD. NADINE COULD BECOME POST-TROPICAL IF IT LOSES MOST OF ITS DEEP CONVECTION DURING THE FORECAST PERIOD...AND THERE IS GREAT UNCERTAINTY AS TO THE TIMING OF WHEN THIS COULD OCCUR. NADINE IS MOVING NORTH-NORTHEASTWARD AT ABOUT 6 KT. THE FORECAST TRACK REMAINS A SIGNIFICANT CHALLENGE AS DIFFERENCES EXIST IN THE MODELS AS TO HOW THE STORM WILL INTERACT WITH A LARGE MID-LATITUDE TROUGH THAT AMPLIFIES OVER THE NORTHEASTERN ATLANTIC IN A COUPLE OF DAYS. NADINE IS FORECAST SLOW DOWN AND MEANDER SOUTHWEST OF THE AZORES DURING THE NEXT DAY OR SO. AFTER THAT TIME...THE TRACK GUIDANCE DIFFERS ON WHETHER THE CYCLONE WILL MOVE SOUTHEASTWARD AND THEN EASTWARD AROUND THE BASE OF THE TROUGH...OR TURN SOUTHWESTWARD AROUND A STRONG DEEP-LAYER RIDGE OVER THE NORTH-CENTRAL ATLANTIC. THE 12Z ECMWF SHOWED THE LATTER SCENARIO...BUT MOST OF THE OTHER GUIDANCE HAS BEEN TRENDING TOWARD A FASTER EASTWARD SOLUTION. THE NEW NHC TRACK FORECAST FAVORS THE EASTWARD SOLUTION AND IS A LITTLE FASTER THAN THE PREVIOUS TRACK...BUT NOT AS FAST AS MUCH OF THE GUIDANCE AND THE TVCA CONSENSUS. THIS MAINTAINS SOME CONTINUITY WITH THE PREVIOUS TRACK AND SHOWS SOME RESPECT FOR THE ECMWF SOLUTION. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 35.8N 32.2W 45 KT 50 MPH 12H 19/1200Z 36.5N 32.0W 45 KT 50 MPH 24H 20/0000Z 36.9N 31.6W 45 KT 50 MPH 36H 20/1200Z 36.4N 30.6W 45 KT 50 MPH 48H 21/0000Z 35.3N 29.0W 45 KT 50 MPH 72H 22/0000Z 34.4N 26.5W 45 KT 50 MPH...POST-TROPICAL 96H 23/0000Z 34.0N 25.0W 45 KT 50 MPH...POST-TROPICAL 120H 24/0000Z 34.0N 24.0W 40 KT 45 MPH...POST-TROPICAL $$ FORECASTER BROWN |