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| #445425 (Received by flhurricane at: 4:37 PM 28.Jul.2011) TCDAT4 TROPICAL STORM DON DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042011 400 PM CDT THU JUL 28 2011 DON HAS A CLASSIC SHEAR PATTERN IN SATELLITE IMAGERY THIS AFTERNOON WITH STRONG BURSTS OF CONVECTION OCCURRING NEAR AND SOUTH OF THE CENTER. ANALYSES FROM THE SHIPS MODEL AND FROM CIMSS AT THE UNIVERSITY OF WISCONSIN INDICATE 10-15 KT OF NORTHERLY VERTICAL WIND SHEAR CONTINUING OVER THE STORM. IN ADDITION...A STREAM OF ARC CLOUDS/GUSTS FRONTS ON THE EASTERN SIDE OF THE CIRCULATION SUGGESTS THAT DRY AIR IS BEING ENTRAINED INTO THE CONVECTION. DATA FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT SHOWED THE CENTRAL PRESSURE RISING TO 1005 MB...WHILE THE AIRCRAFT WINDS SUPPORTED AN INITIAL INTENSITY OF 40 KT. THE INITIAL MOTION IS NOW 305/14. DON REMAINS TO THE SOUTH AND SOUTHWEST OF A DEEP-LAYER RIDGE OVER THE SOUTHEASTERN UNITED STATES...AND THE LARGE-SCALE MODELS FORECAST THIS FEATURE TO PERSIST FOR THE NEXT 36-48 HR. THIS SHOULD STEER DON GENERALLY NORTHWESTWARD TO WEST-NORTHWESTWARD UNTIL LANDFALL ON THE TEXAS COAST IN ABOUT 36 HR. THE TRACK GUIDANCE...WHICH SHIFTED NORTHWARD BETWEEN 06Z AND 12Z...HAS SHIFTED SOUTHWARD FOR THIS ADVISORY. THE NEW FORECAST TRACK HAS BEEN ONLY SLIGHTLY ADJUSTED TO THE SOUTH AND LIES ON THE RIGHT SIDE OF THE GUIDANCE ENVELOPE. SOME ADJUSTMENT TO THE FORECAST TRACK MAY BE NECESSARY IF THE TRACK GUIDANCE STABILIZES AROUND A TRACK SOUTH OF THE CURRENT FORECAST. THE LARGE-SCALE MODELS AGAIN FORECAST MODERATE SHEAR TO CONTINUE UNTIL DON MAKES LANDFALL. THIS AND CONTINUED INTERACTION WITH DRY AIR OVER THE WESTERN GULF OF MEXICO IS LIKELY TO IMPEDE INTENSIFICATION...AND THE INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT DON WILL MAKE LANDFALL AS A TROPICAL STORM AND NOT AS A HURRICANE. THE NEW INTENSITY FORECAST CALLS FOR A LITTLE LESS STRENGTHENING DURING THE FIRST 12-24 HR DUE TO THE PRESENCE OF SHEAR AND ARC CLOUDS...THEN CALLS FOR DON TO REACH A PEAK INTENSITY OF 50 KT NEAR LANDFALL. AFTER LANDFALL...THE CYCLONE SHOULD WEAKEN TO A TROPICAL DEPRESSION BY THE 48 HR POINT AND TO A REMNANT LOW BY THE 72 HR POINT. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 24.9N 91.3W 40 KT 45 MPH 12H 29/0600Z 25.8N 93.1W 40 KT 45 MPH 24H 29/1800Z 26.8N 95.2W 45 KT 50 MPH 36H 30/0600Z 27.8N 97.5W 50 KT 60 MPH...INLAND 48H 30/1800Z 28.8N 100.0W 30 KT 35 MPH...INLAND 72H 31/1800Z 30.5N 103.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 01/1800Z...DISSIPATED $$ FORECASTER BEVEN |
