Tropical Storm BLANCA

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TROPICAL STORM BLANCA DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2 PM PDT TUE JUN 17 2003

THE CYCLONE HAS CONTINUED TO ORGANIZE TODAY...WITH THE LOW-LEVEL
CENTER DISAPPEARING INTO THE CONVECTIVE OVERCAST. SATELLITE
INTENSITY ESTIMATES ARE 45 KT FROM SAB AND AFWA AND 35 KT FROM
TAFB.  BASED ON THIS...TROPICAL DEPRESSION TWO-E IS UPGRADED TO
TROPICAL STORM BLANCA. 
 
THE INITIAL MOTION IS A HIGHLY UNCERTAIN 340/2.  BLANCA IS SITTING
IN A WEAKNESS IN THE SUBTROPICAL RIDGE CAUSED BY MID/UPPER-LEVEL
TROUGHING OVER TEXAS AND NORTHERN MEXICO.  LARGE-SCALE MODELS
FORECAST THIS TROUGH TO BE EVENTUALLY REPLACED BY RIDGING AS A NEW
TROUGH DEVELOPS NEAR THE U. S. WEST COAST.  THIS PATTERN WILL
LIKELY CAUSE SLOW MOTION INITIALLY...FOLLOWED BY A SLIGHTLY FASTER
WESTWARD OR WEST-NORTHWESTWARD MOTION.  WHILE SHOWING SPREAD...NHC
TRACK GUIDANCE GENERALLY AGREES WITH THIS SCENARIO...AND IT HAS
SHIFTED WESTWARD OVER THE PAST SIX HOURS.  THUS...THE FORECAST
TRACK IS ALSO SHIFTED WESTWARD FROM THE PREVIOUS PACKAGE.  IT
SHOULD BE NOTED THAT THE FIRST 24-48 HR OF THE FORECAST IS VERY
UNCERTAIN...AND WATCHES OR WARNINGS COULD BE REQUIRED FOR PORTIONS
OF THE MEXICAN COAST IF BLANCA COMES CLOSER TO LAND THAN CURRENTLY
FORECAST.
 
BLANCA IS IN A DIFFLUENT IF NOT DIVERGENT ENVIRONMENT WITH LIGHT
EASTERLY SHEAR.  LARGE-SCALE MODEL MODELS FORECAST AN INCREASE IN
EASTERLY TO SOUTHEASTERLY SHEAR DURING THE NEXT 72 HR.  THIS
COMBINED WITH GRADUAL MOVEMENT INTO COOLER WATER SHOULD STOP THE
CURRENT ONGOING INTENSIFICATION IN 36-48 HR.  BLANCA IS A SMALL
CYCLONE...AND SHOULD THE CENTRAL CORE CONSOLIDATE IT COULD POSSIBLY
BECOME A HURRICANE BEFORE THE ENVIRONMENT BECOMES LESS FAVORABLE.

LOCALLY HEAVY RAINS ASSOCIATED WITH THE STORM SHOULD CONTINUE TO
SPREAD ONSHORE OVER PORTIONS OF SOUTHWESTERN MEXICO.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      17/2100Z 16.7N 103.6W    40 KT
 12HR VT     18/0600Z 17.0N 103.8W    45 KT
 24HR VT     18/1800Z 17.3N 104.2W    50 KT
 36HR VT     19/0600Z 17.6N 104.7W    55 KT
 48HR VT     19/1800Z 17.9N 105.3W    55 KT
 72HR VT     20/1800Z 18.5N 106.5W    50 KT
 96HR VT     21/1800Z 19.0N 108.0W    40 KT
120HR VT     22/1800Z 19.5N 109.5W    30 KT
 
 
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