MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 10W (LEKIMA) WARNING NR 17// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 10W (LEKIMA), LOCATED APPROXIMATELY 248 NM SOUTH- SOUTHWEST OF KADENA AB, HAS TRACKED NORTH-NORTHWESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION BASED ON A 8 NM EYE IN ANIMATED MULTISPECTRAL SATELLITE IMAGERY. THE INITIAL INTENSITY OF 115 KTS IS CONSISTENT WITH THE PGTW DVORAK CURRENT INTENSITY ESTIMATE OF T6.0 (115 KTS) BUT BELOW THE RJTD DVORAK ESTIMATE OF T6.5 (127 KTS) DUE TO THERE HAVING BEEN ONLY MILD IMPROVEMENT IN THE CONVECTIVE STRUCTURE OVER THE PAST SIX HOURS. TY 10W NO LONGER APPEARS TO BE RAPIDLY INTENSIFYING ALTHOUGH THE ENVIRONMENT SEEMS LIKELY TO SUPPORT THE INTENSITY UNTIL LAND INTERACTION BECOMES A FACTOR. CURRENT FAVORABLE ENVIRONMENTAL CONDITIONS INCLUDE RADIAL OUTFLOW, LOW (5-10 KT) VERTICAL WIND SHEAR (VWS), AND WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURE (SST). TY 10W IS TRACKING ALONG THE SOUTHWEST PERIPHERY OF A SUBTROPICAL RIDGE (STR). 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. THROUGH TAU 24, TY 10W WILL CONTINUE ON ITS CURRENT NORTHWESTWARD TRACK UNDER THE INFLUENCE OF THE STR, START A MORE NORTHWARD TURN PRIOR TO TAU 36 AS THE STR SHIFTS TO THE EAST, AND MAKE LANDFALL SOUTH OF SHANGHAI ON A NORTHWARD TRACK SHORTLY AFTER TAU 48. FAVORABLE ENVIRONMENTAL CONDITIONS WILL ALLOW FOR CONTINUED INTENSIFICATION THROUGH TAU 12. AFTERWARD, REDUCED OUTFLOW AND LAND INTERACTION WILL WEAKEN TY 10W TO 75 KNOTS BY TAU 72. WITH THE CLOSE PROXIMITY OF TAIWAN AND CHINA TO THE FORECAST TRACK, THERE IS HIGH UNCERTAINTY IN THE FORECAST INTENSITY DUE TO THE POTENTIAL FOR ENHANCED LAND INTERACTION. ALTHOUGH ERROR GROWTH IN THE TRACK GUIDANCE STEADILY INCREASES AFTER TAU 12, SPREAD ONLY REACHES 170 NM AT TAU 72 AND THERE IS FAIR CONFIDENCE IN THIS PORTION OF THE FORECAST TRACK. C. AFTER TAU 72, TY 10W WILL CONTINUE TRACKING NORTHWARD ALONG THE WESTERN PERIPHERY OF THE STR UNTIL TURNING NORTH-NORTHWESTWARD PRIOR TO TAU 120 AS THE STR BUILDS TO THE NORTHEAST OF THE SYSTEM. STEADY WEAKENING IS EXPECTED DUE PRIMARILY TO LAND INTERACTION AS THE SYSTEM STRADDLES THE CHINESE COAST ALTHOUGH EVERY ENVIRONMENTAL FACTOR WILL BE SOMEWHAT UNFAVORABLE. BY TAU 120, TY 10W SHOULD BE REDUCED TO 35 KTS AS IT MAKES SECOND LANDFALL ALONG THE COAST OF CHINA. NUMERICAL MODELS GENERALLY DEPICT THE NORTH-NORTHWESTWARD TURN BUT DIFFERENCES IN TIMING OF THE TURN INCREASE THE SPREAD TO OVER 360 NM BY TAU 120. ADDITIONALLY, SEVERAL MODELS KEEP 10W OVER CHINA AFTER MAKING LANDFALL AROUND TAU 48. IF 10W REMAINS OVER LAND AFTER INITIAL LANDFALL, THE SYSTEM WILL LIKELY DISSIPATE PRIOR TO TAU 120. FOR THESE REASONS, THERE IS LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC FORECAST TRACK.// NNNN NNNN