WDPN31 PGTW 100900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING NR 023// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 16W (CHAN-HOM), LOCATED APPROXIMATELY 240 NM SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED EASTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A BROAD, DEFINED LOW-LEVEL CIRCULATION CENTER WITH A WEAK FRONTAL STRUCTURE AND DEEP CONVECTION SHEARED TO THE EAST. OVERALL, THERE IS FAIR CONFIDENCE IN THE INITIAL POSITION AND RECENT TRACK MOTION. A 100714Z ALSO INDICATES AN ASYMMETRIC STRUCTURE WITH SHALLOW BANDING WRAPPING INTO THE CENTER AND DISORGANIZED DEEP CONVECTION DISPLACED TO THE NORTHEAST. THE INITIAL INTENSITY REMAINS ASSESSED AT 50 KNOTS BASED ON RECENT ASCAT DATA; PGTW/RJTD DVORAK CURRENT INTENSITY ESTIMATES RANGE FROM 2.5 TO 3.5 (35 TO 55 KNOTS). ENVIRONMENTAL ANALYSIS REVEALS MARGINAL CONDITIONS WITH STRONG VERTICAL WIND SHEAR (VWS) AND DRY AIR ENTRAINMENT AS WELL AS BAROCLINIC INFLUENCES. THE SYSTEM IS EMBEDDED WITHIN THE ZONAL SUBTROPICAL WESTERLY FLOW AND IS TRACKING EASTWARD ALONG THE SOUTHERN PERIPHERY OF THE BAROCLINIC ZONE. ADDITIONALLY, THERE ARE BROAD LOW-LEVEL SUBTROPICAL RIDGES 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 FORECAST TO DECELERATE AND TURN EAST- SOUTHEASTWARD TO SOUTHEASTWARD THROUGH THE FORECAST PERIOD AS IT STEERS ALONG THE EASTERN PERIPHERY OF THE LOW-LEVEL STR POSITIONED TO THE SOUTHWEST. THE EASTERN STR IS FORECAST TO WEAKEN BUT WILL CONTINUE TO BLOCK EASTWARD PROGRESSION. TS 16W IS FORECAST TO WEAKEN THROUGH THE FORECAST PERIOD UNDER STRONG (30-35 KNOTS) VWS AND DRY AIR ENTRAINMENT WITH DISSIPATION BY TAU 48. NUMERICAL MODEL GUIDANCE DIVERGES BUT SUPPORTS THE SOUTHEASTWARD TRACK WITH FAIR CONFIDENCE.// NNNN