Tropical Storm BLANCA

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TROPICAL STORM BLANCA DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
8 AM PDT WED JUN 18 2003

BLANCA HAS CONSOLIDATED THIS MORNING.  SATELLITE IMAGERY SHOWS A
DEVELOPING CDO...WHILE MEXICAN RADAR FROM CUYUTLAN SHOWS A GOOD...
THOUGH INCORRECTLY NAVIGATED...BANDING PATTERN.  SATELLITE
INTENSITY ESTIMATES ARE 55 KT FROM TAFB AND 45 KT FROM SAB AND
AFWA.  BASED ON THIS...THE INITIAL INTENSITY REMAINS 45 KT. 
HOWEVER...BLANCA MAY BE A LITTLE STRONGER GIVEN THE RADAR
APPEARANCE.
 
THE INITIAL MOTION IS A HIGHLY UNCERTAIN 320/2.  BLANCA REMAINS IN A
WEAKNESS IN THE SUBTROPICAL RIDGE...ALTHOUGH WATER VAPOR IMAGERY
SUGGESTS THAT A RIDGE IS SLOWLY BUILDING BETWEEN THE STORM AND
TROUGHING OVER THE SOUTHERN U. S.  LARGE-SCALE MODELS INDICATE THAT
THE TROUGHING SHOULD BE REPLACED BY A RIDGE AS A NEW TROUGH
DEVELOPS NEAR THE U. S. WEST COAST.  THIS PATTERN SHOULD STEER
BLANCA SLOWLY TO THE WEST OR WEST-NORTHWEST TOWARD A NEW WEAKNESS
IN THE RIDGE.  NHC TRACK GUIDANCE GENERALLY AGREES WITH THIS
SCENARIO.  THE OFFICIAL FORECAST IS THUS AN UPDATE OF THE PREVIOUS
PACKAGE AND IS MORE OR LESS DOWN THE MIDDLE OF THE GUIDANCE.  IT
SHOULD BE NOTED THAT FIRST-LIGHT VISIBLE IMAGES HINT THAT BLANCA
MAY BE FURTHER SOUTH THAN CURRENTLY ANALYZED.  IF SO...THE FORECAST
TRACK WILL NEED TO BE REVISED ON THE NEXT ADVISORY.

BLANCA REMAINS IN A LIGHT-SHEAR EAST-SOUTHEASTERLY UPPER-LEVEL
FLOW...SHOWING GOOD OUTFLOW OVER THE WESTERN SEMICIRCLE. 
LARGE-SCALE MODELS INDICATE THAT UPPER-LEVEL WINDS WILL REMAIN
FAVORABLE FOR 24-36 HR.  AFTER THAT...35-50 KT SOUTHEASTERLIES
SHOULD DEVELOP AND SHEAR THE SYSTEM. BLANCA SHOULD CONTINUE TO
DEVELOP UNTIL THEN...REACHING HURRICANE STRENGTH IN ABOUT 24 HR.
AFTER THAT...A COMBINATION OF SHEAR...COOLER SEA SURFACE
TEMPERATURES...AND DRY AIR SEEN IN WATER VAPOR IMAGERY NORTHWEST OF
THE STORM SHOULD CAUSE WEAKENING.  BLANCA REMAINS A SMALL
CYCLONE...ABOUT 200 N MI IN DIAMETER...AND THUS COULD BOTH
STRENGTHEN AND WEAKEN FASTER THAN CURRENTLY FORECAST.
 
FORECASTER BEVEN
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      18/1500Z 16.8N 104.0W    45 KT
 12HR VT     19/0000Z 17.1N 104.4W    55 KT
 24HR VT     19/1200Z 17.3N 104.9W    65 KT
 36HR VT     20/0000Z 17.5N 105.4W    65 KT
 48HR VT     20/1200Z 17.7N 106.0W    60 KT
 72HR VT     21/1200Z 18.0N 107.5W    50 KT
 96HR VT     22/1200Z 18.0N 109.5W    40 KT
120HR VT     23/1200Z 18.0N 111.5W    25 KT
 
 
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