WDPN32 PGTW 040900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (CHOI-WAN) WARNING NR 08// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 23W (CHOI-WAN), LOCATED APPROXIMATELY 905 NM EAST-NORTHEAST OF ANDERSEN AFB, GUAM HAS TRACKED WEST-NORTHWESTWARD AT 18 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A BETTER CONSOLIDATED STORM WITH INCREASED CONVECTION WRAPPING TOWARDS THE CENTER; HOWEVER, IT IS STILL DEVOID OF CENTRAL CONVECTION LEAVING A LARGE EXPOSED CENTER. THE BULK OF DEEP CONVECTION IS ALONG THE NORTHWESTERN AND SOUTHEASTERN PERIPHERIES. THE INITIAL POSITION IS BASED ON THE CENTER OF THE CENTROID IN THE MSI IMAGERY AND SUPPORTED BY SATELLITE FIXES FROM RJTD AND PGTW WITH FAIR CONFIDENCE. THE INITIAL INTENSITY IS HELD AT 50 KNOTS BASED ON A RECENT SATCON INTENSITY ESTIMATE OF 52 KNOTS AND A DVORAK INTENSITY ESTIMATE OF T3.0 (45 KNOTS) FROM RJTD. UPPER-LEVEL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH RADIAL OUTFLOW, DUE TO A POINT SOURCE, AND LOW VERTICAL WIND SHEAR (VWS). ADDITIONALLY, WARM SEA SURFACE TEMPERATURES (SSTS) ARE CONDUCIVE FOR FURTHER DEVELOPMENT. TS 23W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A DEEP-LAYERED SUB-TROPICAL RIDGE (STR) TO THE NORTH. 3. FORECAST REASONING. A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 23W WILL CONTINUE TRACKING WESTWARD UNDER THE INFLUENCE OF THE STR OVER THE NEXT 36 HOURS. FAVORABLE ENVIRONMENTAL CONDITIONS WILL PERSIST; HOWEVER, DUE TO THE BROAD NATURE OF THE SYSTEM, TS 23W IS EXPECTED TO GRADUALLY INTENSIFY AS IT CONTINUES TO CONSOLIDATE. AFTERWARDS, TS CHOI-WAN IS FORECAST TO ROUND THE STR AND TRACK MORE POLEWARD. AS THE SYSTEM GAINS LATITUDE, IT WILL ENCOUNTER INCREASING VWS AND DECREASING SSTS WHICH WILL BEGIN TO WEAKEN THE SYSTEM. C. BEYOND TAU 72, VWS WILL RAPIDLY INCREASE ABOVE 30 KNOTS AND SSTS WILL DROP BELOW 26 CELSIUS WHICH WILL INCREASE THE RATE OF WEAKENING. TS CHOI-WAN WILL BEGIN TO INTERACT WITH THE BAROCLINIC ZONE NEAR TAU 72 WHICH WILL BEGIN EXTRA-TROPICAL TRANSITION. BY TAU 96, TS 23W WILL BE FULLY EMBEDDED IN THE BAROCLINIC ZONE, GAINING FRONTAL CHARACTERISTICS, AND TRANSITIONING TO A STRONG COLD-CORE LOW. AVAILABLE MODEL GUIDANCE REMAINS IN GOOD AGREEMENT; HOWEVER, GIVEN THE UNCERTAINTY IN THE INITIAL POSITION AND, THEREFORE, THE CURRENT STORM MOTION, THERE IS STILL LOW CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN