MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (MEGI) WARNING NR 12// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 20W (MEGI), LOCATED APPROXIMATELY 355 NM SOUTH OF KADENA AB, HAS TRACKED WEST-NORTHWESTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS SEVERAL DEEP CONVECTIVE RADIAL BANDS WRAPPING TIGHTLY INTO THE LOW LEVEL CIRCULATION CENTER WITHOUT MUCH CHANGE OVER THE LAST SIX HOURS. A DEFINED EYE FEATURE IS STILL ABSENT FROM SATELLITE IMAGERY DESPITE THE INITIAL INTENSITY ASSESSMENT OF 90 KNOTS, WHICH IS BASED ON CURRENT INTENSITY DVORAK ESTIMATES OF T5.0 (90 KNOTS) FROM ALL AGENCIES. THE INITIAL POSITION IS PLACED WITH GOOD CONFIDENCE BASED ON SATELLITE FIXES FROM PGTW AND RJTD. 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, HOWEVER, THE FORECAST TRACK REFLECTS A SLIGHT SHIFT NORTHWARD. 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 60. 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