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