MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (NANGKA) WARNING NR 31// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 11W (NANGKA), LOCATED APPROXIMATELY 855 NM EAST- SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A WEAKENING SYSTEM WITH A CLOUD-FILLED EYE AND SPIRAL BANDING LOCATED PRIMARILY OVER THE SOUTHERN SEMI-CIRCLE DUE TO INCREASING VWS ALONG THE NORTHERN FLANK. THE INITIAL POSITION IS BASED ON A DIMPLE FEATURE IN THE ABOVE ANIMATION WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 100 KNOTS IS SUPPORTED BY DVORAK ESTIMATES FROM PGTW AND RJTD AND REFLECTS THE WEAKENING TREND. THE CYCLONE IS TRACKING ALONG THE SOUTHERN PERIPHERY OF AN EXTENSION OF THE DEEP LAYERED STR TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 11W WILL CONTINUE TO SLOWLY TRACK WESTWARD TO WEST- NORTHWESTWARD UP TO TAU 36 UNDER THE INFLUENCE OF THE STEERING STR. AFTERWARDS, THE SYSTEM WILL BEGIN TO TURN MORE POLEWARD ALONG THE WESTERN PERIPHERY OF THE STR. MARGINALLY-FAVORABLE UPPER-LEVEL CONDITIONS ARE EXPECTED TO CONTINUE, LEADING TO A STEADY WEAKENING TREND THROUGH TAU 48. AFTER TAU 48, TY 11W WILL REVERT TO A NORTHWESTWARD TRACK TOWARD THE RYUKYU ISLANDS AS THE STEERING INFLUENCE TRANSITIONS TO A SECONDARY STR CURRENTLY POSITIONED SOUTH OF MAINLAND JAPAN. VWS IS FORECAST TO DECREASE WITH IMPROVING POLEWARD OUTFLOW, WHICH WILL ALLOW THE SYSTEM TO RE-INTENSIFY. C. IN THE EXTENDED TAUS, TY NANGKA WILL CONTINUE TO STRENGTHEN AS FAVORABLE ENVIRONMENTAL CONDITIONS PERSIST, REACHING 95 KNOTS BY END OF FORECAST. DYNAMIC MODEL GUIDANCE IS IN FAIR AGREEMENT WITH ALL MODELS SHOWING A TRACK TOWARD THE RYUKYU ISLANDS. HOWEVER, THERE IS SIGNIFICANT DIFFERENCES IN THE TRACK SPEED DURING THE INITIAL TURN IN THE FIRST 24-36 HOURS, AND THERE REMAINS A LARGE SPREAD (ABOUT 250 NM) IN THE MODEL SOLUTIONS. IN VIEW OF THIS, THE JTWC TRACK FORECAST CONFIDENCE LEVEL REMAINS LOW.// NNNN NNNN