MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 17W (ATSANI) WARNING NR 22// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUPER TYPHOON (STY) 17W (ATSANI), LOCATED APPROXIMATELY 637 NM EAST- SOUTHEAST OF IWO TO, JAPAN, HAS TRACKED NORTHWESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM HAS BECOME MORE SYMMETRIC AND DEEP WITH FEEDER BANDS WRAPPING TIGHTER INTO AN EXPANDED 34-NM DIAMETER EYE. THE EIR LOOP ALSO SHOWS A SECONDARY EYE IS BEGINNING TO FORM WITHIN THE PRIMARY EYE. THIS EYE WALL REPLACEMENT CYCLE IS CAPTURED IN A 190910Z F18 MICROWAVE PASS. THE INITIAL POSITION IS BASED ON THE EYE FEATURE WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 140 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF DVORAK INTENSITY ESTIMATES FROM ALL REPORTING AGENCIES AND REFLECTS THE IMPROVED STATE OF THE CYCLONE. UPPER-LEVEL ANALYSIS INDICATES THE SYSTEM IS LOCATED IN A FAVORABLE ENVIRONMENT WITH LOW (05 TO 10 KNOT) VWS AND EXCELLENT RADIAL OUTFLOW, AS EVIDENT ON ANIMATED WATER VAPOR IMAGERY. THE CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A STR TO THE NORTHEAST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. STY 17W WILL REMAIN ON A NORTHWESTWARD TRAJECTORY THROUGH TAU 72 UNDER THE STEERING STR. VERY FAVORABLE ENVIRONMENTAL AND UPPER- LEVEL CONDITIONS ARE EXPECTED TO PERSIST ALLOWING THE SYSTEM TO FURTHER INTENSIFY LEADING TO A PEAK INTENSITY OF 145 OVER THE NEXT 24 HOURS. AFTERWARDS, INCREASING VWS WILL BEGIN TO WEAKEN THE SYSTEM. C. IN THE LATER TAUS, AN UPPER-LEVEL TROUGH PASSING TO THE NORTH WILL CAUSE A WEAKNESS IN THE STR, TURNING STY ATSANI MORE POLEWARD. CONCURRENTLY, THE COMBINED EFFECTS OF LOWER OHC VALUES AND INCREASED VWS WILL FURTHER ERODE THE SYSTEM. BY TAU 120, THE SYSTEM WILL ENTER THE COLD BAROCLINIC ZONE AND BEGIN EXTRA-TROPICAL TRANSITION. AVAILABLE MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT LENDING HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN