ZCZC MIATCDEP2 ALL TTAA00 KNHC DDHHMM 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 NNNN
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Page last modified: Monday, 07-Feb-2005 16:49:55 UTC