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.

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