MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING NR 006// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 16W (CHAN-HOM), LOCATED APPROXIMATELY 167 NM WEST-SOUTHWEST OF IWO TO, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT 08 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) AND A 052335Z GMI 89 GHZ MICROWAVE IMAGE REVEALS A DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) WITH DEEP CONVECTION OVER THE EASTERN SEMICIRCLE AND EVIDENT CONVECTIVE BANDING WRAPPING IN FROM THE NORTHWEST. A 052310Z ASCAT-A BULLSEYE IMAGE SHOWS A DEFINED LLCC WITH A SWATH OF 45-49 KT WINDS TO THE EAST, LENDING HIGH CONFIDENCE TO THE INITIAL POSITION. BASED ON THE ASCAT DATA AND DVORAK CURRENT INTENSITY ESTIMATE OF T3.0 (45 KTS) BY PGTW, THERE IS GOOD CONFIDENCE IN THE INITIAL INTENSITY OF 45 KTS. TS 16W IS MOVING THROUGH AN ENVIRONMENT WHICH IS CONDUCIVE FOR DEVELOPMENT WITH WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURES (SST), LOW (5-10 KT) VERTICAL WIND SHEAR (VWS), AND ESTABLISHED EQUATORWARD AND POLEWARD OUTFLOW. THE SYSTEM IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 16W IS FORECAST TO TRACK GENERALLY NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE STEERING STR THROUGH TAU 72, STEADILY INTENSIFYING TO A PEAK OF 80 KTS DUE TO CONTINUED LOW VWS AND WARM SST. DURING THIS TIME, THE STEERING STR WILL BEGIN TO REORIENT. UNCERTAINTY IN THIS REORIENTATION INDUCES UNCERTAINTY IN THE TIMING OF THE RECURVE, INCREASING MODEL SPREAD TO 211 NM BY TAU 72. OVER THE PAST SIX HOURS, THE MODEL SOLUTIONS, AND THUS FORECAST TRACK, HAVE SHIFTED SLIGHTLY WESTWARD. BASED ON THE SPREAD, THERE IS ONLY FAIR CONFIDENCE IN THE INITIAL PORTION OF THE JTWC FORECAST TRACK. C. AFTER TAU 72, THE SYSTEM WILL TRACK FIRST NORTHWARD THEN ROUND THE STR AXIS AND TURN TO A GENERALLY NORTHEASTWARD TRACK TOWARDS KYUSHU. DUE TO HIGH (>20 KTS) VWS, TS 16W IS EXPECTED TO GRADUALLY WEAKEN FOR THE REMAINDER OF THE FORECAST PERIOD TO AN INTENSITY OF 50 KTS BY TAU 120. TS 16W WILL BEGIN TO INTERACT WITH THE BAROCLINIC ZONE DURING THIS TIME AND COMMENCE EXTRATROPICAL TRANSITION. IN THE EXTENDED RANGE, THE ALONG-TRACK SPREAD HAS INCREASED AT TAU 120 DUE TO THE UNCERTAINTY IN THE TIMING OF THE RECURVE. THUS, THERE IS ONLY FAIR CONFIDENCE IN THE REMAINDER OF THE JTWC FORECAST TRACK.// NNNN NNNN