MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W (MALAKAS) WARNING NR 24// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 18W (MALAKAS), LOCATED APPROXIMATELY 276 NM WEST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS THE SYSTEM HAS BECOME MORE ASYMMETRICAL AND ELONGATED WITH SHALLOWER CONVECTION. THE INITIAL POSITION IS BASED ON A LOW REFLECTIVITY MICROWAVE EYE IN THE 171006Z 37GHZ SSMIS PASS AND ALSO REFLECTED AS AN EYE FEATURE ON A COMPOSITE RADAR REFLECTIVITY LOOP FROM MIYAKOJIMA, JAPAN. THE INITIAL INTENSITY OF 100 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF AGENCY AND OBJECTIVE DVORAK ESTIMATES AND REFLECTS THE WEAKENED STATE. UPPER-LEVEL ANALYSIS INDICATES TY 18W HAS DRIFTED INTO THE PREVAILING WESTERLIES. AS SUCH, POLEWARD OUTFLOW HAS INCREASED AND WITH EQUATORWARD OUTFLOW REMAINING ROBUST, VENTILATION OF THE CENTRAL CONVECTION IS ENHANCED. ADDITIONALLY, SEA SURFACE TEMPERATURES AT 28C REMAIN FAVORABLE. HOWEVER, INCREASING VERTICAL WIND SHEAR (VWS) IS OFFSETTING THESE DYNAMICS. THE CYCLONE IS TRACKING ALONG THE 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 TRACK MORE NORTHEASTWARD AND ACCELERATE AS IT ROUNDS THE WESTERN EDGE OF THE STR AND EMBEDS DEEPER INTO THE MID-LATITUDE WESTERLIES. THE SYSTEM WILL MAKE LANDFALL OVER KYUSHU, JAPAN, NEAR TAU 60. INCREASING VWS THEN LAND INTERACTION WILL REDUCE THE CYCLONE TO 45 KNOTS BY TAU 72. C. BEYOND TAU 72, TY MALAKAS WILL DRAG ACROSS THE RUGGED TERRAIN OF THE JAPANESE ALPS. THIS, IN ADDITION TO STRONG VWS (GREATER THAN 40 KNOTS), WILL CAUSE ITS RAPID DISSIPATION OVER HONSHU. THE NUMERIC GUIDANCE IS IN TIGHT AGREEMENT WITH SOME DIFFERENCES IN LATERAL SPEED, LENDING FAIR CONFIDENCE IN THE JTWC TRACK FORECAST.// NNNN NNNN