020 
 WTNT44 KNHC 282034
 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
  
 

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