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| #288799 (Received by flhurricane at: 4:43 PM 16.Aug.2009) TCDAT3 TROPICAL STORM BILL DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009 500 PM AST SUN AUG 16 2009 SATELLITE IMAGES SHOW THAT BILL HAS DEVELOPED A CENTRAL DENSE OVERCAST ALONG WITH IMPRESSIVE BANDING AND OUTFLOW. THESE FEATURES SUGGEST THAT THE STORM CONTINUES TO INTENSIFY. SATELLITE INTENSITY ESTIMATES FROM TAFB/SAB HAVE INCREASED TO T3.5...55 KT ON THE DVORAK SCALE AND THIS VALUE WILL BE USED FOR THE INITIAL WIND SPEED. BILL IS MOVING TOWARD THE WEST-NORTHWEST OR 285/14. THIS GENERAL MOTION IS EXPECTED FOR THE NEXT COUPLE OF DAYS AS A SUBTROPICAL RIDGE SHOULD REMAIN FIRM TO THE NORTH OF THE TROPICAL CYCLONE. THEREAFTER...A COUPLE OF EVOLUTIONS TO THE SYNOPTIC PATTERN SEEM POSSIBLE. THE FIRST...FAVORED BY THE GFS/ECMWF/GFDL/HWRF...SHOWS A MID-LATITUDE SHORTWAVE DIVING INTO THE SUBTROPICAL RIDGE...CAUSING IT TO BREAK AROUND 65W. THIS LEADS TO A NORTHWEST MOTION OF BILL IN ABOUT THREE DAYS. THE OTHER SOLUTION...SHOWN BY THE NOGAPS/UKMET...IS THAT THE HURRICANE BYPASSES THE FIRST BREAK AND CONTINUES MOVING TOWARD THE WEST-NORTHWEST...EVENTUALLY TURNING NORTHWEST AT THE END OF THE FORECAST DUE TO A LARGE MID-LATITUDE TROUGH APPROACHING THE EASTERN UNITED STATES. THE OFFICIAL FORECAST IS SHIFTED A LITTLE BIT TO THE RIGHT AT THE END...IN DEFERENCE TO THE HIGHLY-SKILLED MODELS IN THE FORMER SOLUTION. WATER VAPOR IMAGES SHOW THAT THE HURRICANE IS ON THE SOUTH SIDE OF AN UPPER HIGH WITH LITTLE SHEAR LIKELY FOR THE NEXT SEVERAL DAYS. IN COMBINATION WITH WARM SSTS...THERE IS NO REASON NOT TO FORECAST CONTINUED STRENGTHENING OF BILL. IN FACT...THE SHIPS RAPID INTENSIFICATION INDEX SHOWS A 38 PERCENT CHANCE OF A 30 KT INCREASE IN WINDS DURING THE NEXT 24 HOURS. ALL RELIABLE MODELS CONTINUE TO SHOW THIS SYSTEM BECOMING A MAJOR HURRICANE...WITH THE GFDL/HWRF/GFDN MODELS FORECASTING BILL TO REACH CATEGORY FOUR STRENGTH BY DAY 5. HOWEVER...THERE IS SOME EVIDENCE IN THE GLOBAL MODEL FIELDS THAT THE UPPER-LEVEL WINDS WILL BECOME LESS FAVORABLE AFTER 72 HOURS WITH SOME SOUTHWESTERLY SHEAR DEVELOPING AS BILL BECOMES DISPLACED FROM AN UPPER-LEVEL HIGH. THE OFFICIAL FORECAST WILL SHOW THE INTENSITY LEVELING OFF AFTER THAT TIME DUE TO THAT POSSIBILITY. THE NHC INTENSITY FORECAST IS CLOSE TO THE PREVIOUS FORECAST AND IS SIMILAR TO THE SHIPS MODEL. FORECAST POSITIONS AND MAX WINDS INITIAL 16/2100Z 12.8N 40.0W 55 KT 12HR VT 17/0600Z 13.4N 42.1W 65 KT 24HR VT 17/1800Z 14.2N 45.0W 75 KT 36HR VT 18/0600Z 15.0N 47.7W 85 KT 48HR VT 18/1800Z 16.0N 50.4W 95 KT 72HR VT 19/1800Z 18.5N 55.5W 105 KT 96HR VT 20/1800Z 22.0N 60.5W 105 KT 120HR VT 21/1800Z 26.5N 65.0W 105 KT $$ FORECASTER BLAKE |
