Tropical Storm BLANCA

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TROPICAL STORM BLANCA DISCUSSION NUMBER  15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 AM PDT FRI JUN 20 2003
 
BLANCA HAS HAD ANOTHER MAJOR CONVECTIVE BURST THIS MORNING. 
HOWEVER...FIRST LIGHT VISIBLE IMAGERY INDICATES THE LOW-LEVEL
CENTER IS PARTIALLY EXPOSED ON THE EASTERN SIDE OF THE CONVECTION. 
SATELLITE INTENSITY ESTIMATES ARE 45 KT FROM AFWA...AND 35 KT FROM
TAFB AND SAB.  THE MAXIMUM INTENSITY REMAINS 35 KT IN THIS
ADVISORY.

THE INITIAL MOTION IS A SOMEWHAT UNCERTAIN 265/3.  BLANCA IS ON THE
SOUTH SIDE OF A WEAK SUBTROPICAL RIDGE...WITH LARGE-SCALE MODELS
INDICATING THAT THIS FEATURE WILL PERSIST THROUGH THE FORECAST
PERIOD.  THIS SHOULD KEEP BLANCA ON A SLOW WESTWARD TO
WEST-NORTHWESTWARD TRACK.  MOST NHC GUIDANCE AGREES WITH THIS
SCENARIO...ALTHOUGH ONCE AGAIN THE GUIDANCE IS SPLIT SPEEDWISE
BETWEEN THE SLOWER DYNAMICAL MODELS AND THE FASTER NHC91/BAMD
MODELS.  THE FORECAST TRACK WILL STAY SLOW AND SIMILAR TO THE
PREVIOUS PACKAGE.  ONE ALTERNATE POSSIBILITY IS THAT THE LARGE BUT
DISORGANIZED AREA OF DISTURBED WEATHER SOUTH OF THE GULF OF
TEHUANTEPEC MAY CHANGE THE LOW/MID-LEVEL FLOW ENOUGH FOR BLANCA TO
MOVE EASTWARD...AS INDICATED BY THE GFDN.  SHOULD THAT OCCUR...THE
LARGER DISTURBANCE WOULD LIKELY ABSORB THE SMALLER BLANCA.

BLANCA WILL CONTINUE IN AN ENVIRONMENT OF EASTERLY SHEAR THROUGH
THE FORECAST PERIOD...WITH LARGE-SCALE MODELS INDICATING SOME
INCREASE IN SHEAR AFTER 24 HR.  THIS SHEAR...AIDED BY EXTENSIVE
MID/UPPER-LEVEL DRY AIR AND STABLE LOW-LEVEL STRATOCUMULUS NEAR THE
STORM...SHOULD CAUSE A STEADY WEAKENING EVEN THOUGH BLANCA SHOULD
REMAIN OVER RELATIVELY WARM WATER.  THE INTENSITY FORECAST CALLS
FOR A STEADY-STATE STORM FOR 24 HR FOLLOWED BY SLOW WEAKENING UNTIL
DISSIPATION.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      20/1500Z 15.5N 106.0W    35 KT
 12HR VT     21/0000Z 15.5N 106.6W    35 KT
 24HR VT     21/1200Z 15.6N 107.3W    30 KT
 36HR VT     22/0000Z 15.8N 108.1W    25 KT
 48HR VT     22/1200Z 15.9N 108.8W    25 KT...DISSIPATING
 72HR VT     23/1200Z 16.0N 110.0W    20 KT...REMNANT LOW
 96HR VT     24/1200Z 16.0N 112.0W    20 KT...REMNANT LOW
120HR VT     25/1200Z...DISSIPATED
 
 
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