Tropical Storm BLANCA

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TROPICAL STORM BLANCA DISCUSSION NUMBER  12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2 PM PDT THU JUN 19 2003
 
INTERESTING STRUCTURAL CHANGES OCCURRED WITH BLANCA THIS AFTERNOON. 
SSM/I AND AMSU OVERPASSES FROM 14Z-16Z INDICATED AN EYE WAS
PRESENT.  SINCE THEN...THE CONVECTIVE PATTERN HAS BECOME
FRAGMENTED...SUGGESTING WHATEVER DEVELOPMENT WAS UNDERWAY HAS
STOPPED. SATELLITE INTENSITY ESTIMATES ARE 45 KT FROM SAB AND
AFWA...AND 35 KT FROM TAFB.  THE INITIAL INTENSITY REMAINS 45
KT...BUT THERE IS GREATER THAN NORMAL UNCERTAINTY WITH THAT VALUE. 

BLANCA IS DRIFTING SOUTHWESTWARD IN A WEAKNESS IN THE
SUBTROPICAL RIDGE.  LARGE SCALE-MODELS INDICATE WEAK STEERING
CURRENTS WILL PERSIST THROUGH THE FORECAST PERIOD...WITH SOME
RIDGING DEVELOPING NORTH OF BLANCA GIVING IT A GENERAL WESTWARD
NUDGE.  THE DYNAMICAL MODELS ARE SPREAD BETWEEN A NORTHWESTWARD AND
SOUTHWESTWARD MOTION...BUT ARE UNANIMOUSLY SLOW.  THE BAM MODELS
AND NHC91 CALL FOR A MUCH FASTER WESTWARD TO WEST-NORTHWESTWARD
MOTION.  THE OFFICIAL FORECAST WILL LEAN ON THE SLOW MOTION OF THE
DYNAMICAL MODELS AND IS NUDGED A LITTLE SOUTH OF THE PREVIOUS
FORECAST TRACK.  A COMPLICATING FACTOR IS A LARGE AREA OF DISTURBED
WEATHER FORMING SOUTHEAST OF BLANCA...WHICH MAY TRY TO ABSORB
BLANCA INSTEAD OF LETTING IT MOVE WEST.
 
SOUTHEASTERLY UPPER-LEVEL FLOW IS INCREASING OVER BLANCA...AND THE
RESULTING SHEAR MAY BE CAUSING THE CURRENT CONVECTIVE BREAKDOWN. 
DRY AIR AND STABLE STRATOCUMULUS CLOUDS NEAR THE STORM ARE LIKELY
NOT HELPING MATTERS.  LARGE-SCALE MODELS FORECAST INCREASED SHEAR
FOR THE REST OF THE FORECAST PERIOD...WHICH SHOULD LEAD TO THE
DEMISE OF BLANCA.  THE INTENSITY FORECAST WILL REMAIN STEADY AT 45
KT FOR THE FIRST 24 HR IN CASE THIS UP AND DOWN SYSTEM TRIES TO
INTENSITY ONE MORE TIME...THEN CALLS FOR WEAKENING. ONCE WEAKENING
BEGINS IT MAY BE FASTER THAN CURRENTLY FORECAST.

THE 12 RADII HAVE BEEN REVISED UPWARD BASED ON A REPORT FROM THE
SHIP OXKT2.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      19/2100Z 16.1N 104.9W    45 KT
 12HR VT     20/0600Z 15.9N 105.3W    45 KT
 24HR VT     20/1800Z 15.8N 105.9W    45 KT
 36HR VT     21/0600Z 15.8N 106.6W    40 KT
 48HR VT     21/1800Z 15.9N 107.3W    35 KT
 72HR VT     22/1800Z 16.0N 108.5W    30 KT
 96HR VT     23/1800Z 16.0N 110.0W    25 KT...DISSIPATING
120HR VT     24/1800Z 16.0N 111.5W    20 KT...REMNANT LOW
 
 
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