MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (NEOGURI) WARNING NR 016// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 21W (NEOGURI), LOCATED APPROXIMATELY 142 NM SOUTH- SOUTHEAST OF KADENA AB, OKINAWA, HAS TRACKED NORTHEASTWARD AT 14 KNOTS OVER THE PAST SIX HOURS. TY 21W IS CURRENTLY INTERACTING WITH A DEEP MIDLATITUDE SHORTWAVE TROUGH SITUATED OVER THE EAST CHINA SEA, THEREFORE, EXTRA-TROPICAL TRANSITION (ETT) HAS COMMENCED. THE 20/00Z NAZE SOUNDING (47909) INDICATES A SOUTH-SOUTHWESTERLY JET WITH 75-85 KNOTS AT 300-200MB, WHICH IS PRODUCING VERY STRONG (40-50 KNOTS) VERTICAL WIND SHEAR (VWS) AND ROBUST POLEWARD OUTFLOW. AS REVEALED IN RADAR IMAGERY, THE SYSTEM HAS RETAINED AN EYE DESPITE THE BULK OF THE DEEP CONVECTION SHEARING TO THE NORTH-NORTHEAST. THERE IS GOOD CONFIDENCE IN THE CURRENT POSITION BASED ON THE RADAR IMAGERY AND CORRESPONDING RJTD RADAR FIXES. THE CURRENT INTENSITY IS ASSESSED CONSERVATIVELY AT 80 KNOTS BASED ON THE CONVECTIVE STRUCTURE AND DVORAK INTENSITY ESTIMATES OF 4.0/5.0 FROM RJTD AND PGTW. AFTER A SHORT-TERM NORTHEASTWARD TRAJECTORY OVER THE PAST SIX HOURS, RADAR IMAGERY NOW INDICATES THAT TY 21W IS TRACKING NORTH- NORTHEASTWARD AGAIN. FORTUNATELY, THE COMPACT SYSTEM REMAINS WELL TO THE SOUTHEAST OF OKINAWA, WHICH IS REPORTING SUSTAINED WINDS OF 10- 15 KNOTS WITH GUSTS UP TO 25 KNOTS. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 21W IS FORECAST TO TRACK NORTH-NORTHEASTWARD THROUGH TAU 24 WITHIN THE STRONG SOUTH-SOUTHWESTERLY FLOW BETWEEN THE AFOREMENTIONED SHORTWAVE TROUGH AND THE STR POSITIONED TO THE EAST. VWS IS EXPECTED TO INCREASE SIGNIFICANTLY (> 65 KNOTS) BY TAU 36 AS THE SYSTEM TRACKS UNDER THE JET AND RAPIDLY COMPLETES ETT. CONSEQUENTLY, RAPID WEAKENING IS ANTICIPATED. NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT ONLY THROUGH TAU 36 THEN DIVERGES WITH INCREASING UNCERTAINTY IN THE CENTER POSITION AND FORECAST TRACK AS THE SYSTEM GAINS FRONTAL CHARACTERISTICS AND THE CENTER BROADENS. AFTER THE SYSTEM TRANSITIONS TO AN EXTRA-TROPICAL, COLD-CORE LOW, THE CURRENT JTWC FORECAST IS EXTENDED TO 72 HOURS AS A COURTESY TO ASSETS IN JAPAN DUE TO THE PRESENCE OF GALE-FORCE WINDS THROUGHOUT THE FORECAST PERIOD. IN GENERAL, THE LATEST RUN OF MODEL GUIDANCE HAS IMPROVED SIGNIFICANTLY WITH A MORE COHESIVE DEPICTION OF THE SYSTEM TRACKING SOUTH AND EAST OF HONSHU. OVERALL, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN