ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM HECTOR DISCUSSION NUMBER 20 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092006 800 AM PDT SUN AUG 20 2006 A HELPFUL TRMM MICROWAVE PASS AT 1020 UTC SHOWED THAT THE LOW-LEVEL CENTER OF HECTOR HAS DECOUPLED FROM THE MIDDLE-LEVEL CENTER PREVIOUSLY SEEN ON THE NIGHT-VIS IMAGERY... REQUIRING A SMALL SOUTHWARD ADJUSTMENT TO THE INITIAL POSITION. RECENT SATELLITE PICTURES SHOW THAT THE EYE FEATURE HAS DISSIPATED AND CONVECTION HAS SHIFTED EXCLUSIVELY TO THE EASTERN SEMICIRCLE OF THE STORM... CONSISTENT WITH THE IMPACTS OF WESTERLY SHEAR. DVORAK ESTIMATES FROM SAB/TAFB ARE DROPPING AS QUICKLY AS THE RULES ALLOW AND THE INITIAL INTENSITY IS LOWERED TO 60 KT. A FAST WEAKENING IS LIKELY DUE TO INCREASING WESTERLY SHEAR... COLD SSTS DROPPING BELOW 24C... AND PLENTY OF STABLE AIR AS DIAGNOSED BY SHIPS. THE INTENSITY FORECAST IS IN GOOD AGREEMENT WITH SHIPS AND THE FSU SUPERENSEMBLE... CALLING FOR THE TROPICAL CYCLONE TO DISSIPATE TOMORROW. THE MOTION FOR THE PAST 12 HOURS IS ABOUT 300/9. THIS GENERAL MOTION SHOULD CONTINUE FOR ABOUT A DAY UNTIL THE CYCLONE LOSES MOST OF ITS DEEP CONVECTION. THEREAFTER A WEST-NORTHWEST TURN IS ANTICIPATED AS HECTOR BECOMES A SHALLOW SYSTEM STEERED BY THE LOWER-LEVEL FLOW. MOST MODEL GUIDANCE SEEMS TO BE HOLDING ONTO A STRONG VERTICALLY-STACKED SYSTEM FOR TOO LONG... LEADING TO A NORTHWESTWARD OR EVEN NORTHWARD MOTION. THE OFFICIAL FORECAST WILL STAY ON THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE... CLOSE TO A COMPOSITE OF THE GFS ENSEMBLE... BAM SHALLOW... AND THE UKMET. THE WEST-NORTHWEST TURN COULD OCCUR SOONER THAN FORECAST IF THE CYCLONE WEAKENS FASTER THAN SHOWN BELOW. FORECAST POSITIONS AND MAX WINDS INITIAL 20/1500Z 19.8N 133.5W 60 KT 12HR VT 21/0000Z 20.5N 134.7W 45 KT 24HR VT 21/1200Z 21.3N 136.1W 30 KT 36HR VT 22/0000Z 22.0N 137.5W 25 KT...REMNANT LOW 48HR VT 22/1200Z 22.5N 139.0W 20 KT...REMNANT LOW 72HR VT 23/1200Z 23.0N 142.5W 20 KT...REMNANT LOW 96HR VT 24/1200Z...DISSIPATED $$ FORECASTER BLAKE/FRANKLIN NNNN
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Page last modified: Monday, 11-Sep-2006 11:28:42 UTC