MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (MALAKAS) WARNING NR 25// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 18W (MALAKAS), LOCATED APPROXIMATELY 93 NM NORTHEAST OF TAIPEI, TAIWAN, HAS TRACKED NORTHWARD AT 02 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS WARMING CONVECTIVE CLOUD TOPS, AND A BROADENING CIRCULATION OVER THE PAST 12 HOURS INDICATING THE SYSTEM HAS WEAKENED. A 171908Z AMSU 89 GHZ IMAGE ALSO REVEALS A DECREASE IN DEEP CONVECTION ALONG THE WESTERN SEMICIRCLE WHERE DRY AIR IS BEGINNING TO IMPINGE ON THE SYSTEM. THE CURRENT BEST TRACK POSITION IS SUPPORTED BY THE AFOREMENTIONED IMAGERY WITH GOOD CONFIDENCE. THE INITIAL INTENSITY OF 85 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF AGENCY AND OBJECTIVE DVORAK ESTIMATES AND REFLECTS THE WEAKENED STATE. UPPER-LEVEL ANALYSIS INDICATES A MARGINALLY FAVORABLE ENVIRONMENT WITH GOOD OUTFLOW OFFSET BY MODERATE (15 TO 20 KNOTS) VERTICAL WIND SHEAR (VWS). SEA SURFACE TEMPERATURES REMAIN FAVORABLE (AROUND 28C), HOWEVER OCEAN HEAT CONTENT VALUES REMAINS UNFAVORABLE FOR DEVELOPMENT. THE CYCLONE IS TRACKING ALONG THE WESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE EAST-NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 18W IS EXPECTED TO BEGIN TRACKING ON A MORE NORTHEASTWARD TRAJECTORY AND ACCELERATE AS IT ROUNDS THE WESTERN PERIPHERY OF THE STR AND EMBEDS DEEPER INTO THE STRONG MID-LATITUDE WESTERLIES. THIS SYSTEM IS FORECAST TO WEAKEN GRADUALLY THROUGH THE FIRST 48 HOURS AS VWS SLOWLY INCREASES. THE SYSTEM WILL MAKE LANDFALL OVER KYUSHU, JAPAN, JUST AFTER TAU 48. C. BEYOND TAU 72, TY MALAKAS WILL THE SYSTEM WILL CONTINUE ACCELERATING NORTHEASTWARD ALONG COASTAL JAPAN WITHIN THE WESTERLIES. VWS WILL BECOME INCREASINGLY UNFAVORABLE, RESULTING IN RAPID WEAKENING OF THE SYSTEM. TC 18W IS FORECAST TO FULLY DISSIPATE BY TAU 96, JUST OFFSHORE OF TOKYO. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE FORECAST TRACK, HOWEVER THERE ARE SOME DIFFERENCES IN THE SPEED OF MOVEMENT OF TY MALAKAS, ESPECIALLY AFTER TAU 48. THEREFORE, THERE IS FAIR CONFIDENCE IN THE JTWC TRACK FORECAST.// NNNN NNNN