868 
 WTNT44 KNHC 280840
 TCDAT4
  
 TROPICAL STORM DON DISCUSSION NUMBER   3
 NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
 400 AM CDT THU JUL 28 2011
  
 DON HAS NOT CHANGED APPRECIABLY DURING THE PAST SEVERAL HOURS...
 MAINTAINING A SMALL AREA OF CONVECTION NEAR THE CENTER.  THERE IS
 NOT MUCH ORGANIZATION IN THE INFRARED CLOUD PATTERN...WHICH IS
 CONFIRMED BY A TRMM MICROWAVE PASS AT 0608Z. ASCAT DATA FROM 0332Z
 SUPPORTED AN INITIAL INTENSITY OF AROUND 35 KT...WITH SATELLITE
 CLASSIFICATIONS AT OR BELOW THAT VALUE.  THE ASCAT DATA CONFIRMED
 THE EARLIER AIRCRAFT MEASUREMENTS THAT DON IS A RATHER SMALL
 TROPICAL CYCLONE.  THE NEXT AIRCRAFT MISSION IS SCHEDULED FOR 1200Z
 THIS MORNING.
  
 THE INTENSITY FORECAST IS TRICKY.  WHILE THE LARGE-SCALE ENVIRONMENT
 DOES NOT APPEAR TO HAVE MUCH SHEAR...THE LOW- AND MID-LEVEL CENTERS
 ARE NOT WELL-ALIGNED INITIALLY...WHICH WAS APPARENT ON A 2316Z
 SSMIS MICROWAVE IMAGE. THE GFS/ECMWF MODELS HAVE A REASONABLE
 REPRESENTATION OF THIS INITIAL STRUCTURE AND KEEP THE CENTERS FROM
 VERTICALLY STACKING...POSSIBLY WHY THESE MODELS DO NOT SHOW
 MUCH INTENSIFICATION.  WHILE THE STATISTICALLY MODELS STILL
 FORECAST STEADY STRENGTHENING...THE HWRF/GFDL MODELS FORECAST A
 SLOW DECLINE.  ANOTHER FACTOR TO CONSIDER IS THAT THE SIZE OF DON
 MAKES IT SUSCEPTIBLE TO RAPID CHANGES IN STRENGTH...BOTH UP AND
 DOWN...THAT ARE NEARLY IMPOSSIBLE TO FORECAST.  GIVEN THE REDUCED
 ORGANIZATION...THE NHC INTENSITY FORECAST IS LOWERED SOMEWHAT FROM
 THE PREVIOUS FORECAST...BUT IS STILL ON THE UPPER END OF THE
 GUIDANCE ENVELOPE NEAR A COMPOSITE OF THE SHIPS/LGEM MODELS.
  
 BEST ESTIMATE OF INITIAL MOTION IS 300/9... WITH OVERNIGHT MICROWAVE
 IMAGES SUGGESTING THE SMALL CENTER HAS BEEN MOVING ERRATICALLY.  DON
 IS MOVING AROUND THE SOUTHERN PERIPHERY OF A RIDGE OVER THE
 SOUTHERN UNITED STATES.  THIS RIDGE IS FORECAST TO BUILD SLIGHTLY
 DURING THE NEXT DAY OR TWO AS A SERIES OF WEAK IMPULSES MOVE AWAY
 FROM THE NORTHERN GULF COAST.  THIS SYNOPTIC PATTERN SHOULD STEER
 THE CYCLONE GENERALLY TO THE WEST-NORTHWEST AND ACCELERATE IT.  THE
 TRACK GUIDANCE HAS SHIFTED A BIT TO THE WEST OVERNIGHT WITH LESS
 SPREAD THAN EARLIER.  THIS SHIFT TO THE LEFT SEEMS REASONABLE WITH
 THE BUILDING RIDGE AND THE NHC FORECAST WILL BE MOVED IN THAT
 DIRECTION...BUT STILL LIES TO THE RIGHT OF THE MODEL CONSENSUS.
  
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  28/0900Z 23.0N  88.7W   35 KT  40 MPH
  12H  28/1800Z 23.9N  90.3W   40 KT  45 MPH
  24H  29/0600Z 25.1N  92.5W   45 KT  50 MPH
  36H  29/1800Z 26.3N  94.7W   50 KT  60 MPH
  48H  30/0600Z 27.3N  97.1W   50 KT  60 MPH
  72H  31/0600Z 29.0N 101.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
  96H  01/0600Z...DISSIPATED
  
 $$
 FORECASTER BLAKE/BROWN