MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (FRANCISCO) WARNING NR 19// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 09W (FRANCISCO), LOCATED APPROXIMATELY 47 NM SOUTHEAST OF BUSAN, SOUTH KOREA, HAS TRACKED NORTHWESTWARD AT 18 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS THE SYSTEM REMAINS INTACT AS IT EXITED KYUSHU INTO THE TSUSHIMA STRAIT; HOWEVER, THE CENTRAL CONVECTION APPEARS TO BE ERODING AS EVIDENCED BY WARMING TOPS AND ELONGATION ALONG THE NORTHERN FLANKS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A DEFINED LOW LEVEL CIRCULATION ON A COMPOSITE RADAR LOOP FROM NORTHERN KYUSHU. THE INITIAL INTENSITY OF 50 KNOTS IS HELD SLIGHTLY LOWER THAN AGENCY FIXES TO REFLECT THE RAPID WEAKENING TREND. THE INITIAL POSITION AND INTENSITY ARE SUPPORTED BY NEARBY SURFACE OBSERVATIONS INCLUDING THOSE FROM TSUSHIMA ISLAND, 10 NM TO THE WEST. ENVIRONMENTAL ANALYSIS SHOWS TS 09W HAS DRIFTED INTO INCREASING SOUTHEASTERLY VERTICAL WIND SHEAR (20 TO 25 KNOTS) CAUSING A SLIGHT FORWARD TILT. THE VWS IS PARTLY OFFSET BY EXCELLENT POLEWARD OUTFLOW AND MARGINAL SST (26 CELSIUS). THE CYCLONE IS TRACKING UNDER THE INFLUENCE OF A SUBTROPICAL RIDGE (STR) LOCATED TO THE EAST-NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE OVERALL FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 09W WILL CONTINUE TO TRACK NORTHWESTWARD THROUGH TAU 12 UNDER THE STR, MAKING LANDFALL NEAR BUSAN WITHIN SIX HOURS. AFTER TAU 12, IT WILL BEGIN TO ROUND THE STR AXIS AND TURN NORTHWARD THEN NORTHEAST- TO EAST-NORTHEASTWARD, DRAG ALONG THE EASTERN SOUTH KOREAN MOUNTAIN RANGE, THEN CROSS THE SEA OF JAPAN (SOJ) BEFORE MAKING LANDFALL OVER HOKKAIDO BY TAU 72. INCREASING VWS, LAND INTERACTION, AND COOLING SSTS IN THE SOJ WILL CONTINUE TO RAPIDLY ERODE THE SYSTEM. CONCURRENTLY, BY TAU 36, IT WILL BEGIN EXTRA-TROPICAL TRANSITION IN THE SOJ AND MAINTAIN A LARGE WIND FIELD. BY TAU 72, TS 09W WILL BECOME A COLD CORE LOW AFTER IT MAKES LANDFALL IN HOKKAIDO. NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT, LENDING HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN