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#545724 (Received by flhurricane at: 10:53 AM 26.Sep.2012) TCDAT4 TROPICAL STORM NADINE DISCUSSION NUMBER 56 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142012 1100 AM AST WED SEP 26 2012 NADINE HAS BECOME BETTER ORGANIZED THIS MORNING. VISIBLE IMAGERY SHOWS INCREASING CONVECTIVE BANDING IN THE NORTHERN SEMICIRCLE... ALONG WITH DEVELOPING ANTICYCLONIC CIRRUS OUTFLOW. A RECENT ASCAT OVERPASS SHOWED SEVERAL 40-KT VECTORS IN THE NORTHWEST QUADRANT... AND SUGGESTS THAT THE RADIUS OF MAXIMUM WIND HAS CONTRACTED TO ABOUT 40 N MI. THE INITIAL INTENSITY IS INCREASED TO 45 KT...BASED ON THE ASCAT DATA. THE STORM HAS BEEN MOVING SOUTHWARD FOR THE PAST SEVERAL HOURS... WITH THE INITIAL MOTION 180/3. THE TRACK GUIDANCE IS 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 BECOMES DIVERGENT AFTER 72 HR DUE TO DIFFERENCES IN THE FORECAST FORWARD SPEED OF NADINE AND WHETHER THE STORM WILL RECURVE INTO THE WESTERLIES AHEAD OF AN APPROACHING MID-/ UPPER-LEVEL TROUGH. THE CANADIAN MODEL SHOWS THE TROUGH ACCELERATING NADINE TO THE NORTHEAST...WHILE THE NOGAPS...GFDL... AND HWRF SHOW THE CYCLONE STALLING NEAR THE 120 HR POINT. THE UKMET AND ECMWF SHOW THE TROUGH BYPASSING NADINE TO THE NORTH... WITH RIDGING BEHIND THE TROUGH CAUSING THE CYCLONE TO AGAIN MOVE SOUTHWARD. THE GFS...IN A SIGNIFICANT SHIFT FROM ITS PREVIOUS FORECAST...IS NOW MORE IN LINE WITH THE UKMET AND ECMWF. GIVEN THE UNCERTAINTY...THE TRACK FORECAST CALLS FOR A SLOW MOTION AFTER THE 96 HR POINT. THE NEW TRACK IS SIMILAR TO THE PREVIOUS TRACK AND IS NEAR THE CENTER OF THE TRACK GUIDANCE ENVELOPE. NADINE IS MOVING OVER INCREASING SEA SURFACE TEMPERATURES. THE SHIPS MODEL AND ANALYSES FROM CIMSS SUGGEST THE CYCLONE IS IN A LIGHT SHEAR ENVIRONMENT...ALTHOUGH WATER VAPOR IMAGERY SUGGESTS THE POSSIBILITY THAT SOME NORTHERLY UPPER-LEVEL FLOW IS UNDERCUTTING THE OUTFLOW. THE INTENSITY GUIDANCE FORECASTS A RELATIVELY FAVORABLE ENVIRONMENT TO CONTINUE FOR ABOUT 36 HR...AND THE INTENSITY FORECAST SHOWS SLOW INTENSIFICATION DURING THIS TIME. AFTER 36 HR...INCREASING WESTERLY SHEAR AND A MOTION OVER COOLER WATERS SHOULD HALT INTENSIFICATION AND CAUSE A GRADUAL WEAKENING. THE INTENSITY FORECAST IS SIMILAR TO THE SHIPS AND THE INTENSITY CONSENSUS THROUGH 48 HR...AND IS LOWER THAN THOSE MODELS AFTER THAT. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 30.6N 30.3W 45 KT 50 MPH 12H 27/0000Z 29.8N 30.9W 45 KT 50 MPH 24H 27/1200Z 28.9N 32.0W 45 KT 50 MPH 36H 28/0000Z 28.7N 33.4W 50 KT 60 MPH 48H 28/1200Z 29.4N 34.5W 50 KT 60 MPH 72H 29/1200Z 32.0N 36.0W 50 KT 60 MPH 96H 30/1200Z 35.0N 36.5W 45 KT 50 MPH 120H 01/1200Z 36.0N 37.0W 45 KT 50 MPH $$ FORECASTER BEVEN |