WDPN31 PGTW 102100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING NR 025// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 16W (CHAN-HOM), LOCATED APPROXIMATELY 187 NM SOUTH OF YOKOSUKA, JAPAN, HAS TRACKED EASTWARD AT 13 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A BROAD, PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH A WEAK FRONTAL STRUCTURE AND DEEP CONVECTION SHEARED TO THE EAST. OVERALL, THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION AND RECENT TRACK MOTION. A 101643Z ATMS 88.2 GHZ MICROWAVE IMAGE INDICATES DEEPER CONVECTION DISPLACED TO THE NORTHEAST AND WEAK SHALLOW BANDING WRAPPING INTO A LLCC. BASED ON PGTW AND RJTD DVORAK CURRENT INTENSITY ESTIMATES OF T3.0 (45 KTS), THE INITIAL INTENSITY REMAINS ASSESSED AT 50 KTS, SUPPORTED BY RECENT ASCAT DATA REVEALING 45-50 KT WINDS TO THE NORTH OF THE LLCC. ENVIRONMENTAL ANALYSIS SHOWS MARGINAL CONDITIONS AND IS CHARACTERIZED BY STRONG VERTICAL WIND SHEAR (VWS) AND INCREASING DRY AIR ENTRAINMENT. ADDITIONALLY, TS 16W IS EXPERIENCING BAROCLINIC INFLUENCES AS THE SYSTEM IS EMBEDDED WITHIN THE ZONAL SUBTROPICAL WESTERLY FLOW AND TRACKING ALONG THE SOUTHERN PERIPHERY OF THE BAROCLINIC ZONE. ADDITIONALLY, THERE ARE BROAD LOW-LEVEL SUBTROPICAL RIDGES (STR) ENTRENCHED TO THE EAST AND SOUTHWEST OF THE SYSTEM. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. DUE TO THE PRESENCE OF THE AFOREMENTIONED LOW-LEVEL SUBTROPICAL RIDGES, TS 16W IS EXPECTED TO DECELERATE AND TURN SOUTHEASTWARD THEN SOUTHWARD THROUGH THE FORECAST PERIOD. THE SYSTEM WILL STEER ALONG THE EASTERN PERIPHERY OF THE LOW-LEVEL STR LOCATED TO THE SOUTHWEST. ALTHOUGH THE EASTERN STR IS FORECAST TO WEAKEN, IT WILL CONTINUE TO BLOCK THE EASTWARD PROGRESSION OF THE SYSTEM. DUE TO INCREASING (25-35 KT) VWS AND CONTINUED DRY AIR ENTRAINMENT, TS 16W SHOULD WEAKEN THROUGHOUT THE FORECAST PERIOD WITH DISSIPATION EXPECTED BY TAU 48. NUMERICAL MODEL GUIDANCE DIVERGES AS THE SYSTEM TURNS SOUTHWARD, BUT LENDS OVERALL SUPPORT THE JTWC FORECAST TRACK WITH FAIR CONFIDENCE.// NNNN