WDPN31 PGTW 091500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING NR 020// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 16W (CHAN-HOM), LOCATED APPROXIMATELY 382 NM SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED EAST- NORTHEASTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER WITH ASSOCIATED CONVECTION SHEARED TO THE NORTHEAST. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE PRESENCE OF THE FULLY EXPOSED LLCC AND THE LOW LEVEL FEATURES PRESENT IN A 091216Z AMSU 89GHZ IMAGE. THE 55KTS INITIAL INTENSITY IS ALSO PLACED WITH HIGH CONFIDENCE BASED ON MULTIAGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T3.5 (55 KTS, RJTD AND PGTW) AND A CIMSS 091214Z SATCON INTENSITY ESTIMATE OF 54 KTS. TS CHAN-HOM IS TRACKING ALONG THE NORTHERN PERIPHERY OF A SUBTROPICAL RIDGE POSITIONED TO THE SOUTH AND THROUGH AN UNFAVORABLE ENVIRONMENT FOR CONTINUED DEVELOPMENT WITH HIGH (30+ KTS) VERTICAL WIND SHEAR (VWS) OFFSET SLIGHTLY BY WARM (26-27 CELSIUS) SEA SURFACE TEMPERATURES AND ROBUST OUTFLOW ALOFT THAT IS ASSOCIATED WITH THE JET POSITIONED OVER JAPAN. THE SYSTEM IS TRACKING NEAR THE BAROCLINIC ZONE AND HAS BEGUN EXTRATROPICAL TRANSITION (ETT). 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS CHAN-HOM WILL CONTINUE TO TRACK EAST-NORTHEASTWARD THROUGH TAU 24 AS IT CONTINUES TO UNDERGO ETT. CONTINUED HIGH VWS WILL LEAD TO A FURTHER WEAKENING TO 45 KTS BY THIS TIME. A REORIENTATION OF THE THE STEERING RIDGE WILL LEAD TO A GENERALLY EASTWARD TRACK BETWEEN TAU 24 AND TAU 36 BY WHICH TIME TS 16W WILL COMPLETE ETT. VWS WILL REMAIN HIGH AND LEAD TO FURTHER WEAKENING DESPITE WARM SST TO 35 KTS BY TAU 48. THERE REMAINS A SIGNIFICANT SPREAD IN NUMERICAL MODEL TRACK GUIDANCE THROUGH THE FORECAST PERIOD, HOWEVER MODEL SOLUTIONS HAVE FURTHER CONVERGED ON AN ULTIMATE SOUTHEASTWARD CURVE IN THE TRACK AFTER TAU 36. THE ACROSS TRACK SPREAD IN SOLUTIONS INCREASES FROM 97 NM AT TAU 36 TO 196 NM AT TAU 48, INDICATING AN INCREASING DIVERGENCE IN THE TRACKS OF THE JTWC MULTI-MODEL CONSENSUS MEMBERS. THIS DIVERGENCE IN TRACK GUIDANCE LENDS OVERALL POOR CONFIDENCE IN THE JTWC FORECAST TRACK, WHICH IS PLACED NEAR THE MULTI-MODEL CONSENSUS.// NNNN