000 WTNT43 KNHC 230859 TCDAT3 TROPICAL STORM BONNIE DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032010 500 AM EDT FRI JUL 23 2010 THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING BONNIE HAS FOUND LITTLE CHANGE IN STRENGTH. THE AIRCRAFT HAS MEASURED A PEAK 850 MB FLIGHT-LEVEL WIND OF 42 KT...BELIEVABLE SFMR WINDS OF 34 KT...AND A MINIMUM PRESSURE OF 1008 MB. THESE DATA SUPPORT MAINTAINING AN INITIAL INTENSITY OF 35 KT. THE AIRCRAFT DATA SUGGEST THAT THE CIRCULATION HAS BECOME LESS DEFINED AS FEW WEST OR NORTHWEST WINDS WERE FOUND. IF THIS TREND CONTINUES...IT IS POSSIBLE FOR BONNIE TO DEGENERATE TO AN OPEN TROUGH. FOR NOW...THE OFFICIAL FORECAST ASSUMES THAT BONNIE WILL BE ABLE TO MAINTAIN A CLOSED CIRCULATION AND REMAIN A TROPICAL CYCLONE. AS BONNIE PASSED THROUGH THE CENTRAL BAHAMAS...AN OBSERVING SITE ON STANIEL CAY REPORTED A SUSTAINED WIND OF 37 KT. THE AIRCRAFT FIXES SHOW THAT BONNIE IS MOVING FASTER AND HAS TURNED WEST-NORTHWESTWARD. THE INITIAL MOTION ESTIMATE IS 295/16. BONNIE IS FORECAST TO MAINTAIN THIS GENERAL HEADING DURING THE NEXT DAY OR SO AS IT MOVES AROUND THE SOUTHWESTERN SIDE OF A MID- TO UPPER- LEVEL RIDGE CENTERED OVER THE CAROLINAS. THE TRACK GUIDANCE IS GOOD AGREEMENT DURING FIRST 48 HOURS...BUT THERE IS SOME SPREAD IN THE GUIDANCE AFTER LANDFALL ALONG THE NORTHERN GULF COAST. THE GUIDANCE IS NOTICEABLY FASTER...WHICH MAY BE IN PART FROM THE MORE WESTWARD INITIAL LOCATION. THE NEW NHC TRACK IS SIMILAR TO THE PREVIOUS TRACK BUT IS FASTER THAN THE PREVIOUS ADVISORY. THIS REQUIRES THE ISSUANCE OF TROPICAL STORM WATCHES FOR A PORTION OF THE NORTHERN GULF COAST. THE UPPER-AIR ENVIRONMENT AHEAD OF BONNIE IS LESS THAN IDEAL FOR STRENGTHENING. BONNIE IS EXPECTED TO REMAIN UNDER THE INFLUENCE OF MODERATE TO STRONG SOUTHEASTERLY SHEAR DUE TO THE FLOW BETWEEN AN UPPER-LEVEL LOW OVER THE GULF OF MEXICO AND THE AFOREMENTIONED RIDGE. THE UPPER-LEVEL FLOW IS FORECAST BY THE GLOBAL MODELS TO WEAKEN IN 36-48 HOURS...WHICH COULD ALLOW FOR SOME STRENGTHENING OF BONNIE. THE OFFICIAL FORECAST IS BETWEEN THE MORE AGGRESSIVE SHIPS/LGEM GUIDANCE AND THE HWRF/GFDL MODELS WHICH SHOWS LITTLE... IF ANY...INTENSIFICATION. FORECAST POSITIONS AND MAX WINDS INITIAL 23/0900Z 24.1N 78.6W 35 KT 12HR VT 23/1800Z 25.0N 81.0W 40 KT 24HR VT 24/0600Z 26.2N 84.1W 40 KT 36HR VT 24/1800Z 27.6N 86.9W 45 KT 48HR VT 25/0600Z 28.8N 89.1W 45 KT 72HR VT 26/0600Z 31.5N 92.0W 25 KT...INLAND 96HR VT 27/0600Z 34.5N 93.0W 20 KT...POST-TROP/REMNT LOW 120HR VT 28/0600Z...DISSIPATED $$ FORECASTER BROWN/LANDSEA