Tropical Storm DON

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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
 
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