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| #445352 (Received by flhurricane at: 11:03 AM 28.Jul.2011) TCDAT4 TROPICAL STORM DON DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042011 1000 AM CDT THU JUL 28 2011 THE CENTER OF DON REMAINS PARTLY EXPOSED ON THE NORTH SIDE OF A PERSISTENT AREA OF CONVECTION THIS MORNING. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT HAS TWICE EXTRAPOLATED A MINIMUM PRESSURE OF 1001 MB. THE AIRCRAFT HAS ALSO REPORTED 850 MB FLIGHT-LEVEL WINDS OF 52 KT AND RELIABLE-LOOKING WINDS OF 35-40 KT FROM THE SFMR. BASED ON THIS...THE INITIAL INTENSITY IS INCREASED TO 40 KT. THE INITIAL MOTION IS NOW 305/12. DON IS 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 BETWEEN 36-48 HR. WHILE THE TRACK GUIDANCE AGREES ON THIS SCENARIO...THERE HAS BEEN A SIGNIFICANT NORTHWARD SHIFT IN THE GUIDANCE SINCE THE PREVIOUS ADVISORY...WITH THE CENTER OF THE GUIDANCE ENVELOPE NOW NORTH OF CORPUS CHRISTI. THE NEW TRACK FORECAST WILL ALSO SHIFT NORTHWARD BUT STAYS TO THE SOUTH OF THE CENTER OF THE NEW GUIDANCE ENVELOPE. IT SHOULD BE NOTED THAT THE ECMWF AND UKMET FORECAST TRACKS ARE ON THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE TO THE SOUTH OF THE CURRENT FORECAST TRACK. ANALYSES FROM THE SHIPS MODEL AND FROM CIMSS AT THE UNIVERSITY OF WISCONSIN SHOW THAT DON IS EXPERIENCING 10-15 KT OF NORTHERLY VERTICAL WIND SHEAR. LIGHT/MODERATE SHEAR IS NOW FORECAST TO CONTINUE UNTIL THE CYCLONE MAKES LANDFALL. IN ADDITION...THE CYCLONE IS ON THE EDGE OF AN AREA OF DRY AIR IN THE WESTERN GULF OF MEXICO. THESE FACTORS COULD AT LEAST SLOW INTENSIFICATION...AND NONE OF THE INTENSITY GUIDANCE CURRENTLY SHOWS DON BECOMING A HURRICANE BEFORE LANDFALL. THE NEW INTENSITY FORECAST IS BASICALLY AN UPDATE OF THE PREVIOUS PACKAGE IN BEST AGREEMENT WITH THE SHIPS MODEL. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 24.1N 90.1W 40 KT 45 MPH 12H 29/0000Z 24.9N 91.5W 45 KT 50 MPH 24H 29/1200Z 26.1N 93.8W 50 KT 60 MPH 36H 30/0000Z 27.3N 96.0W 50 KT 60 MPH 48H 30/1200Z 28.5N 98.2W 40 KT 45 MPH...INLAND 72H 31/1200Z 30.0N 102.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 01/1200Z...DISSIPATED $$ FORECASTER BEVEN |
