MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (MEGI) WARNING NR 13// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 20W (MEGI), LOCATED APPROXIMATELY 343 NM SOUTH OF KADENA AB, HAS TRACKED WEST-NORTHWESTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS TIGHT SPIRAL BANDING WRAPPING TIGHTLY INTO THE LOW LEVEL CIRCULATION CENTER. A 10 NM RAGGED EYE FEATURE FORMED BRIEFLY OVER THE LAST SIX HOURS, WHICH WAS ALSO OBSERVED IN A 252239Z SSMIS 91GHZ IMAGE GIVING HIGH CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY IS ASSESSED AT 90 KTS, AND IS BASED ON CURRENT INTENSITY DVORAK ESTIMATES OF T5.0 (90 KNOTS) FROM ALL AGENCIES. UPPER-LEVEL ANALYSIS SHOWS EXCELLENT RADIAL OUTFLOW OVER THE SYSTEM, TAPPING INTO THE WESTERLY MID-LATITUDE JET TO THE NORTH AND A LARGE TUTT CELL TO THE EAST. VERTICAL WIND SHEAR IS VERY LOW (5 TO 10 KNOTS) AND SSTS ARE ALSO FAVORABLE, NEAR 30 CELSIUS. CURRENTLY TY MEGI IS TRACKING NORTHWEST ALONG THE PERIPHERY OF A BUILDING DEEP-LAYERED SUBTROPICAL RIDGE POSITIONED TO THE NORTHEAST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. TY MEGI WILL CONTINUE ITS NORTHWESTERN TRACK ALONG THE CURRENT STEERING RIDGE THAT WILL CONTINUE TO BUILD THROUGHOUT THE FORECAST PERIOD. SLIGHT INTENSIFICATION IS EXPECTED THROUGH TAU 24 REACHING A PEAK INTENSITY OF 100 KNOTS UNDER FAVORABLE ENVIRONMENTAL CONDITIONS. RAPID WEAKENING WILL ENSUE FOLLOWING LANDFALL OVER THE MOUNTAINOUS REGION OF CENTRAL TAIWAN AROUND TAU 36. TY MEGI IS EXPECTED TO EMERGE OVER WATER OFF THE WESTERN SHORE OF TAIWAN REORGANIZING AS A TROPICAL STORM, THEN MAKE LANDFALL AGAIN OVER CHINA NEAR TAU 54. RAPID DISSIPATION IS EXPECTED AS TY MEGI TRACKS FURTHER INLAND FULLY DISSIPATING BY TAU 96. DYNAMIC MODEL GUIDANCE IS IN VERY GOOD AGREEMENT WITH ONLY MINOR DIFFERENCES IN TRACK LOCATION AND SPEED. THE FORECAST TRACK IS PLACED NEAR THE MULTI- MODEL CONSENSUS WITH HIGH CONFIDENCE.// NNNN NNNN