MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (PEIPAH) WARNING NR 05// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 17W (PEIPAH), LOCATED APPROXIMATELY 270 NM NORTH-NORTHEAST OF SAIPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 21 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY AND A 151530Z AMSR2 37 GHZ MICROWAVE IMAGE SHOW THE LOW LEVEL CIRCULATION CENTER FULLY EXPOSED. FOR THAT REASON, THERE IS HIGH CONFIDENCE IN THE INITIAL POSITION. THE INITIAL INTENSITY OF 35 KTS IS PLACED ON THE HIGH SIDE OF THE PGTW DVORAK CURRENT INTENSITY ESTIMATE OF T2.0 (30 KTS) TO ACCOUNT FOR THE SYSTEM TRACKING AT 21 KTS. DESPITE STRONG EQUATORWARD OUTFLOW AND WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURE (SST), THE ENVIRONMENT IS UNFAVORABLE DUE TO HIGH (35-40 KT) VERTICAL WIND SHEAR (VWS). TS 17W IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A NORTH-TO-SOUTH ORIENTED SUBTROPICAL RIDGE (STR). 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. FOR THE DURATION OF THE FORECAST, TS 17W WILL TRACK NORTHWESTWARD ALONG THE STR. THE ENVIRONMENT IS EXPECTED TO REMAIN HOSTILE AND THE CIRCULATION IS EXPECTED TO FALL BELOW WARNING THRESHOLD BY TAU 36. THE FORECAST TRACK CLOSELY FOLLOWS THE CONSENSUS BUT, WITH SPREAD IN THE MODEL GUIDANCE EXCEEDING 200 NM BY TAU 36, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN