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| #543314 (Received by flhurricane at: 10:56 PM 16.Sep.2012) TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 23 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 1100 PM AST SUN SEP 16 2012 THE SATELLITE PRESENTATION OF NADINE HAS DEGRADED SINCE THIS AFTERNOON WITH LESS CONVECTION NEAR THE CENTER AND A MORE ASYMMETRIC APPEARANCE. RECENT MICROWAVE IMAGES ALSO SHOW THAT THE LOW-LEVEL CENTER IS DISPLACED TO THE SOUTHWEST OF THE PRIMARY CONVECTIVE BAND. AS A RESULT...DVORAK T-NUMBERS HAVE DECREASED AND THE INITIAL INTENSITY IS LOWERED TO 60 KT...WHICH IS A BLEND OF THE LATEST AND T- AND CI-NUMBERS. ALTHOUGH VERTICAL SHEAR IS FORECAST TO DECREASE A LITTLE DURING THE NEXT DAY OR SO...IT IS EXPECTED TO REMAIN MODERATE TO STRONG OVER THE NEXT 72 HOURS. THE SHEAR ALONG WITH GRADUALLY DECREASING SSTS SHOULD INDUCE SOME WEAKENING...HOWEVER MUCH OF THE INTENSITY GUIDANCE AND THE GLOBAL MODELS SHOW LITTLE OVERALL CHANGE IN STRENGTH OVER THE NEXT COUPLE OF DAYS. THE LACK OF WEAKENING COULD BE DUE TO THE INTERACTION OF NADINE AND A SHORT-WAVE TROUGH APPROACHING THE CYCLONE FROM THE WEST. THE NHC FORECAST IS IN GOOD AGREEMENT WITH THE GUIDANCE AND ONLY PREDICTS A SLIGHT DECREASE IN INTENSITY DURING THE NEXT SEVERAL DAYS. MICROWAVE DATA DURING THE PAST 6-12 HOURS SUGGESTS THAT NADINE IS BEGINNING TO SLOW DOWN AND HAS TURNED EAST-NORTHEASTWARD. THE INITIAL MOTION ESTIMATE IS 075/16 KT. AN ADDITIONAL REDUCTION IN FORWARD SPEED AND A TURN TOWARD THE NORTHEAST ARE EXPECTED DURING THE NEXT DAY OR TWO AS A MID-LEVEL RIDGE SLIDES EASTWARD TO THE NORTH OF NADINE AND A CUT-OFF LOW FORMS TO THE WEST OF THE CYCLONE. THE MODEL GUIDANCE IS IN GOOD AGREEMENT DURING THE FIRST 2 TO 3 DAYS OF THE FORECAST PERIOD. AFTER THAT TIME...ANOTHER MID- TO UPPER-LEVEL LOW IS FORECAST TO MOVE SOUTHWARD OVER THE NORTHEASTERN ATLANTIC. AS THIS OCCURS...THE TRACK GUIDANCE BECOME QUITE DIVERGENT AS THEY DEPICT VARYING INTERACTIONS OF NADINE AND THE UPPER-LOW. GIVEN THE LARGE SPREAD IN THE GUIDANCE...THE NHC FORECAST REMAINS NEAR THE MODEL CONSENSUS AT DAYS 4 AND 5. ALTHOUGH NADINE HAS RECENTLY TAKEN ON A LESS TROPICAL APPEARANCE IN SATELLITE DUE TO AN APPROACHING TROUGH...THE GLOBAL MODELS SUGGEST THIS TROUGH WILL NOT BE STRONG ENOUGH TO CAUSE NADINE TO TRANSITION INTO AN EXTRATROPICAL CYCLONE. INSTEAD...THE GFS AND ECMWF INDICATE THAT AS THE TROPICAL CYCLONE INTERACTS WITH THE CUT-OFF LOW IN A FEW DAYS...NADINE WILL THEN TRANSITION INTO AN EXTRATROPICAL CYCLONE...AND THIS TRANSFORMATION IS FORECAST TO BE COMPLETE IN ABOUT 5 DAYS. FORECAST POSITIONS AND MAX WINDS INIT 17/0300Z 31.4N 38.1W 60 KT 70 MPH 12H 17/1200Z 32.1N 35.8W 55 KT 65 MPH 24H 18/0000Z 33.2N 33.9W 55 KT 65 MPH 36H 18/1200Z 34.4N 32.9W 55 KT 65 MPH 48H 19/0000Z 35.6N 32.5W 55 KT 65 MPH 72H 20/0000Z 37.0N 31.5W 50 KT 60 MPH 96H 21/0000Z 37.5N 29.5W 50 KT 60 MPH 120H 22/0000Z 37.5N 28.5W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ FORECASTER BROWN |
