WDPN33 PGTW 101500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (NANGKA) WARNING NR 29// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 11W (NANGKA), LOCATED APPROXIMATELY 890 NM EAST- SOUTHEAST OF KADENA AB, HAS TRACKED WESTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY DEPICTS A WEAKENING SYSTEM WITH A CLOUD-FILLED EYE AND SPIRAL BANDING LOCATED PRIMARILY OVER THE SOUTHERN SEMI-CIRCLE DUE TO INCREASING NORTHERLY VERTICAL WIND SHEAR (VWS). A 101157Z METOP-B 89 GHZ IMAGE ALSO SHOWS THE DECAYING CONVECTIVE STRUCTURE WITH AN ERODING EYEWALL OVER THE NORTHERN QUADRANT. BASED ON THE EYE, THERE IS HIGH CONFIDENCE IN THE CURRENT POSITION. ANIMATED WATER VAPOR IMAGERY DEPICTS GOOD EQUATORWARD OUTFLOW, HOWEVER, INCREASING NORTHERLY FLOW AND INCREASED VWS IS HAMPERING CONVECTIVE DEVELOPMENT OVER THE NORTHERN SEMI-CIRCLE. THEREFORE, THE CURRENT INTENSITY IS NOW ASSESSED SLIGHTLY LOWER AT 110 KNOTS BASED ON DECREASING DVORAK INTENSITY ESTIMATES OF T5.0/6.0 FROM PGTW. TY NANGKA IS TRACKING ALONG THE SOUTHERN PERIPHERY OF AN EXTENSION OF THE DEEP LAYERED SUB- TROPICAL RIDGE (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 TRACK WESTWARD TO WEST-NORTHWESTWARD THROUGH TAU 24 UNDER THE DOMINANT STEERING STR. MARGINALLY-FAVORABLE UPPER-LEVEL CONDITIONS ARE EXPECTED TO CONTINUE, LEADING TO A MARKED, STEADY WEAKENING TREND THROUGH TAU 72. AFTER TAU 24, TY NANGKA WILL SLOW AND BEGIN TO TURN POLEWARD ALONG THE WESTERN PERIPHERY OF A RE-ORIENTING STR. DYNAMIC GUIDANCE IS IN BETTER AGREEMENT, HOWEVER, THERE REMAINS SIGNIFICANT UNCERTAINTY IN THE TIMING AND DEGREE OF THE POLEWARD TRACK CHANGE. C. IN THE EXTENDED TAUS, TY 11W WILL TURN NORTHWESTWARD TOWARD THE RYUKYU ISLANDS AS THE STEERING INFLUENCE TRANSITIONS TO THE STR POSITIONED SOUTH OF MAINLAND JAPAN. VWS IS FORECAST TO DECREASE WITH IMPROVING POLEWARD OUTFLOW NEAR TAU 120, WHICH WILL ALLOW THE SYSTEM TO RE-INTENSIFY. DYNAMIC MODEL GUIDANCE IS IN FAIR AGREEMENT WITH ALL MODELS NOW SHOWING A TRACK TOWARD THE RYUKYU ISLANDS. DUE TO THE LARGE SPREAD OF ABOUT 300 NM IN THE MODEL SOLUTIONS AT TAU 120, THE JTWC TRACK FORECAST CONFIDENCE LEVEL REMAINS LOW.// NNNN