514 
 WTNT44 KNHC 290839
 TCDAT4
  
 TROPICAL STORM DON DISCUSSION NUMBER   7
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
 400 AM CDT FRI JUL 29 2011
  
 DON CONTINUES TO HAVE A SHEARED APPEARANCE ON SATELLITE IMAGES WITH
 THE LOW-LEVEL CENTER DISPLACED NEAR THE NORTHERN EDGE OF AN
 ELONGATED AREA OF STRONG CONVECTION.  THIS SHEAR CAN ALSO BE SEEN
 IN RECONNAISSANCE DATA...WHICH SHOWED THAT THE SURFACE CENTER IS
 DISPLACED SOMEWHAT TO THE NORTH OF THE 850 MB FLIGHT-LEVEL CENTER. 
 THE INITIAL INTENSITY REMAINS 45 KT...A BLEND OF THE ESTIMATES FROM
 SATELLITE AND AIRCRAFT DATA.
  
 MODERATE NORTHERLY SHEAR IS FORECAST UNTIL DON MAKES LANDFALL ALONG
 WITH SOME DRY AIR ALOFT.  THIS COMBINATION WILL PROBABLY LIMIT
 SIGNIFICANT INTENSIFICATION EVEN THOUGH THE STORM IS MOVING OVER
 VERY WARM WATERS.  MOST OF THE GUIDANCE SHOWS JUST A LITTLE MORE
 STRENGTHENING...AND THE OFFICIAL INTENSITY FORECAST IS BASICALLY AN
 UPDATE OF THE PREVIOUS PACKAGE.  AFTER MOVING THROUGH TEXAS...THIS
 SMALL SYSTEM WILL NOT LAST VERY LONG AFTER INTERACTING WITH THE
 HIGH TERRAIN OF MEXICO...AND DISSIPATION IS LIKELY BETWEEN 36 AND
 48 HOURS.
  
 AIRCRAFT FIXES SUGGEST DON IS MOVING ABOUT 295/12.  HIGH PRESSURE
 RIDGING OVER THE SOUTHERN UNITED STATES WILL PROBABLY STEER THE
 CYCLONE ALONG THAT GENERAL COURSE UNTIL LANDFALL...PERHAPS EVEN A
 LITTLE MORE TO THE LEFT AS THE RIDGE BUILDS.  THE GUIDANCE IS IN
 GOOD AGREEMENT...ALTHOUGH THE USUALLY RELIABLE ECMWF MODEL IS
 FARTHER TO THE NORTHEAST.  AN EXAMINATION OF THE ECMWF FIELDS
 INDICATES THAT THE MODEL DECOUPLES THE LOW- AND MID-LEVEL
 CENTERS...ALLOWING DON TO MOVE MORE TO THE NORTHWEST.  THIS DOES
 NOT SEEM LIKELY AS ENVIRONMENTAL CONDITIONS ARE NOT EXPECTED TO
 CHANGE SIGNIFICANTLY FROM NOW UNTIL LANDFALL.  THUS THE NHC
 FORECAST WILL STAY CLOSE TO THE DYNAMICAL MODEL CONSENSUS AND THE
 PREVIOUS FORECAST.
  
 INTERESTS IN EXTREME NORTHEAST MEXICO SHOULD CLOSELY MONITOR THE
 PROGRESS OF DON. AN UNEXPECTED SMALL DEVIATION TO THE SOUTH OF THE
 FORECAST TRACK COULD NECESSITATE THE ISSUANCE OF WARNINGS FOR THE
 EXTREME NORTHEASTERN COAST OF MEXICO.
 
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  29/0900Z 25.3N  93.6W   45 KT  50 MPH
  12H  29/1800Z 26.1N  95.5W   50 KT  60 MPH
  24H  30/0600Z 27.0N  97.8W   45 KT  50 MPH...INLAND
  36H  30/1800Z 27.8N 100.4W   30 KT  35 MPH...INLAND
  48H  31/0600Z...DISSIPATED
  
 $$
 FORECASTER BLAKE/STEWART
  
 

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