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| #545779 (Received by flhurricane at: 4:38 PM 26.Sep.2012) TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 57 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 500 PM AST WED SEP 26 2012 NADINE CONTINUES TO PRODUCE ORGANIZED CONVECTIVE BANDING...NOW PRIMARILY OVER THE SOUTHWESTERN SEMICIRCLE. AN EARLIER OSCAT OVERPASS SHOWED 40 KT WINDS IN THE NORTHWESTERN QUADRANT...AND THE SATELLITE INTENSITY ESTIMATED FROM TAFB HAS INCREASED TO 45 KT. BASED ON THESE...THE INITIAL INTENSITY REMAINS 45 KT. NADINE IS PRODUCING GOOD CIRRUS OUTFLOW IN ALL DIRECTIONS EXCEPT FOR THE SOUTHEAST. HOWEVER...DROPSONDES FROM THE NASA GLOBAL HAWK AIRCRAFT NORTH OF NADINE SHOW 35-40 KT NORTHERLY WINDS ADVECTING DRY AIR TOWARD THE STORM. LATER DROPSONDES SHOULD HELP DETERMINE HOW MUCH OF THESE WINDS/DRY AIR ARE ACTUALLY REACHING THE CORE OF NADINE. THE INITIAL MOTION IS NOW 200/4. THE TRACK GUIDANCE REMAINS IN GOOD AGREEMENT FOR THE NEXT 48-72 HR...FORECASTING NADINE TO TURN SOUTHWESTWARD...WESTWARD...AND THEN NORTHWESTWARD AROUND A DEEP-LAYER RIDGE MOVING EASTWARD ACROSS THE NORTHEASTERN ATLANTIC. THE GUIDANCE AGAIN BECOMES VERY DIVERGENT AFTER 72 HR. WHILE THE MODELS NOW AGREE THAT NADINE WILL NOT RECURVE AHEAD OF A MID/UPPER-LEVEL TROUGH...THERE CONTINUE TO BE MAJOR DIFFERENCES IN THE DIRECTION OF MOTION AFTER 96 HR. THE GFDL...GFS...AND GFS ENSEMBLE MEAN SHOW A SLOW MOTION TOWARD THE EAST OR NORTHEAST. THE ECMWF...UKMET...AND NOGAPS SHOW A TURN TOWARD THE WEST OR SOUTHWEST DUE TO RIDGING IN THE WAKE OF THE TROUGH. FINALLY...THE HWRF AND THE CANADIAN SHOW LITTLE MOTION. THE NEW FORECAST TRACK HAS MINOR ADJUSTMENTS DURING THE FIRST 48 HR...AND THEN IS SIMILAR TO THE PREVIOUS FORECAST THEREAFTER. GIVEN THE MODEL SPREAD AFTER 96 HR...THE NEW FORECAST IS FOR A VERY SLOW MOTION DURING THIS TIME. THE NEW TRACK REMAINS NEAR THE CENTER OF THE GUIDANCE ENVELOPE. THE INTENSITY FORECAST IS UNCERTAIN DUE TO A COMPLICATED UPPER-LEVEL WIND PATTERN NEAR NADINE. FIRST IS THE 400 MB NORTHERLY WINDS MENTIONED ABOVE AND THEIR POSSIBLE IMPACT ON THE STORM. SECOND... WATER VAPOR IMAGERY SHOWS AN UPPER-LEVEL LOW NEAR 29N47W...WITH A TROUGH EXTENDING EASTWARD TO JUST SOUTH OF NADINE. STRONG UPPER- LEVEL WESTERLY WINDS ARE OCCURRING JUST SOUTH OF THE TROUGH...BUT ARE CURRENTLY NOT AFFECTING THE TROPICAL CYCLONE. THE GLOBAL MODELS ALL FORECAST INCREASING UPPER-LEVEL WINDS NEAR NADINE AFTER 36 HR. HOWEVER...THEY ALL SHOW THAT THE UPPER-LEVEL TROUGH COULD CONTINUE TO SHELTER NADINE FROM THE WORST OF THE SHEAR. FINALLY... MOST OF THE GLOBAL MODELS SHOW NADINE MERGING WITH THE UPPER-LEVEL LOW BY 120 HR...WHICH COULD CHANGE THE STRUCTURE OF THE CYCLONE. PROBABLY THE LEAST COMPLICATED PART OF THIS FORECAST IS THAT NADINE SHOULD MOVE OVER COOLER SEA SURFACE TEMPERATURES AFTER 36 HR. THE INTENSITY GUIDANCE GENERALLY SHOWS SLOW STRENGTHENING THROUGH 48-72 HR. DUE TO THE POSSIBILITY THAT SHEAR AND DRY AIR WILL AFFECT NADINE...THE INTENSITY FORECAST CALLS FOR A SHORTER WINDOW FOR STRENGTHENING...WITH A PEAK INTENSITY IN 24-36 HR. IT ALSO CALLS FOR LESS INTENSIFICATION THAN THE SHIPS...LGEM...AND INTENSITY CONSENSUS MODELS. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 30.2N 30.8W 45 KT 50 MPH 12H 27/0600Z 29.4N 31.5W 45 KT 50 MPH 24H 27/1800Z 28.8N 32.8W 50 KT 60 MPH 36H 28/0600Z 29.0N 34.2W 50 KT 60 MPH 48H 28/1800Z 29.7N 35.3W 50 KT 60 MPH 72H 29/1800Z 32.5N 36.5W 50 KT 60 MPH 96H 30/1800Z 35.5N 37.0W 45 KT 50 MPH 120H 01/1800Z 36.0N 37.0W 45 KT 50 MPH $$ FORECASTER BEVEN |
