ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM DON DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042011 400 PM CDT WED JUL 27 2011 AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE TROPICAL WAVE OVER THE SOUTHERN GULF OF MEXICO FOUND A CLOSED SURFACE CIRCULATION WITH A CENTRAL PRESSURE OF 1001 MB. THE MAXIMUM 1000 FT FLIGHT-LEVEL WINDS WERE 45 KT EAST OF THE CENTER... AND THERE WERE SEVERAL RELIABLE-LOOKING SMFR SURFACE WIND ESTIMATES OF 35 KT. BASED ON THIS...THE SYSTEM IS DESIGNATED AS TROPICAL STORM DON. THE AIRCRAFT DATA SHOW THAT THE CIRCULATION CENTER IS ELONGATED...AND IT IS POSSIBLE SOME REFORMATION OF THE CENTER COULD OCCUR TONIGHT IN RESPONSE TO CONVECTIVE BURSTS. THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 295/10. DON IS SOUTH OF A LOW/MID-LEVEL RIDGE OVER THE NORTHERN GULF OF MEXICO...AND WATER VAPOR IMAGERY SHOWS UPPER-LEVEL EASTERLY FLOW DEVELOPING TO THE NORTH AND NORTHEAST OF THE STORM. THE LARGE-SCALE MODELS FORECAST THAT WITHIN 24 HR DON WILL BECOME EMBEDDED IN DEEP-LAYER EASTERLY TO SOUTHEASTERLY FLOW THAT SHOULD PERSIST FOR SEVERAL DAYS. THIS EVOLUTION SHOULD STEER THE STORM GENERALLY NORTHWESTWARD. WHILE THE MODELS AGREE WITH THIS SCENARIO...THERE IS A SPREAD IN THE GUIDANCE ON WHERE DON WILL REACH THE NORTHWESTERN GULF COAST. THE GFDL AND GFS ARE FARTHEST TO THE RIGHT...CLOSER TO THE HOUSTON/ GALVESTON AREA. THE UKMET/ECMWF ARE FARTHEST TO THE LEFT...CLOSER TO THE BROWNSVILLE AREA. THE FORECAST TRACK LIES BETWEEN THESE EXTREMES AND IS CLOSE TO THE VARIOUS CONSENSUS MODELS. DON IS OVER THE WARM WATERS OF THE GULF OF MEXICO...AND THE GLOBAL MODELS FOR THE MOST PART FORECAST LIGHT TO MODERATE VERTICAL WIND SHEAR OVER THE SYSTEM FOR THE NEXT 72 HR. DESPITE THIS...NONE OF THOSE MODELS SUGGEST SIGNIFICANT STRENGTHENING OF THE STORM...AND NEITHER DOES THE GFDL. THE SHIPS...LGEM...AND HWRF MODELS FORECAST THE SYSTEM TO REACH 55-65 KT BEFORE LANDFALL IN TEXAS...AND THE INTENSITY FORECAST FOLLOWS THAT SCENARIO IN BEST AGREEMENT WITH THE SHIPS MODEL. IT SHOULD BE NOTED THAT THE 48 HR INTENSITY OF 55 KT IS WELL BEFORE LANDFALL...AND DON COULD GET STRONGER THAN THIS BETWEEN 48-72 HR. WATCHES AND/OR WARNINGS WILL LIKELY BE REQUIRED FOR PORTIONS OF THE TEXAS COAST TONIGHT OR THURSDAY. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 22.2N 87.0W 35 KT 40 MPH 12H 28/0600Z 23.1N 88.7W 40 KT 45 MPH 24H 28/1800Z 24.5N 90.9W 45 KT 50 MPH 36H 29/0600Z 25.8N 92.8W 50 KT 60 MPH 48H 29/1800Z 27.1N 94.8W 55 KT 65 MPH 72H 30/1800Z 29.0N 99.5W 35 KT 40 MPH...INLAND 96H 31/1800Z 31.0N 103.0W 25 KT 30 MPH...INLAND 120H 01/1800Z...DISSIPATED $$ FORECASTER BEVEN NNNN
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Page last modified: Tuesday, 17-Jul-2012 13:43:44 UTC