WDPN31 PGTW 020300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (TORAJI) WARNING NR 03// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 15W (TORAJI), LOCATED APPROXIMATELY 124 NM WEST OF KADENA AB, HAS TRACKED EAST-NORTHEASTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LOW-LEVEL CIRCULATION CENTER (LLCC) THAT HAS CONTINUED TO CONSOLIDATE AND DEEPENING CONVECTION THAT HAS STARTED TO WRAP AROUND THE LLCC. RADAR IMAGERY FROM OKINAWA, JAPAN, SHOWS A GOOD IMPROVEMENT IN STRUCTURE AS CONVECTIVE BANDING IS WRAPPING TIGHTER INTO THE LLCC. THE INITIAL POSITION IS BASED ON THE MSI LOOP, THE RADAR IMAGERY AND A 012344Z SSMIS 37 GHZ MICROWAVE IMAGE WITH FAIR CONFIDENCE. THE INITIAL INTENSITY HAS BEEN INCREASED TO 35 KNOTS BASED ON A DVORAK INTENSITY ESTIMATE OF THE SAME VALUE FROM RJTD AND THE IMPROVEMENT IN STRUCTURE SEEN IN THE RADAR LOOP ALONG WITH THE MICROWAVE IMAGE. UPPER-LEVEL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT CHARACTERIZED BY LOW TO MODERATE (10 TO 20 KNOTS) VERTICAL WIND SHEAR (VWS) AND GOOD EQUATORWARD AND POLEWARD OUTFLOW. TS 15W IS CURRENTLY TRACKING ALONG THE SOUTHERN PERIPHERY OF THE PASSING DEEP MID-LATITUDE TROUGH NORTHWEST OF THE SYSTEM. 3. FORECAST REASONING. A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. THE SYSTEM IS EXPECTED TO CONTINUE TRACKING TO THE NORTHEAST THROUGH TAU 36. BETWEEN TAU 36 AND TAU 72 THE SYSTEM WILL ENTER AN AREA OF WEAK ENVIRONMENTAL STEERING AND TRACK SPEEDS WILL SLOW AS THE TROUGH PASSES THROUGH AND A SUBTROPICAL RIDGE (STR) IS EXPECTED TO BUILD ACROSS KYUSHU. AS THIS RIDGE BUILDS, TS 15W WILL TURN MORE POLEWARD ALONG THE WESTERN PERIPHERY OF THIS BUILDING STR. THE INTENSITY OF TS 15W IS EXPECTED TO GRADUALLY INCREASE THROUGH TAU 36 TO A PEAK OF 50 KTS UNDER FAVORABLE UPPER LEVEL CONDITIONS. AFTER TAU 36, INCREASING VWS FROM THE TROUGH AND BUILDING RIDGE WILL START TO WEAKEN THE SYSTEM. C. IN THE EXTENDED TAUS, TS 15W IS EXPECTED TO TRACK POLEWARD ALONG THE WESTERN PERIPHERY ON THE STR. ONCE IT CROSSES THE RIDGE AXIS NEAR TAU 96, THE SYSTEM WILL START TO TRACK NORTHEASTWARD TOWARDS THE SEA OF JAPAN. TS 15W WILL START TO INTERACT WITH THE BAROCLINIC ZONE AND MID-LATITUDE WESTERLIES AS IT IS DRIVEN POLEWARD BY THE BUILDING RIDGE NEAR TAU 72. THIS WILL BEGIN EXTRATROPICAL TRANSITION WITH COMPLETION BY TAU 96 AS IT WILL BE FULLY EMBEDDED IN BAROCLINIC ZONE. DYNAMIC MODEL GUIDANCE IS IN FAIRLY TIGHT AGREEMENT WITH THE NORTHEAST TRACK THROUGH TAU 36, ALTHOUGH AT VARYING TRACK SPEEDS. AFTER TAU 36, UNCERTAINTY SIGNIFICANTLY INCREASES AS A BIFURCATION REMAINS IN THE GUIDANCE. NAVGEM, ECMWF, AND THE JAPANESE ENSEMBLE SHOW THE RIDGE BUILDING IN MUCH STRONGER WHICH IS GREATLY WEAKENING THE SYSTEM AND DRIVING THE WEAKENED VORTEX NORTHWEST IN THE EXTENDED TAUS. GFS, COAMPS, AND THE GFS ENSEMBLE, HOWEVER, CONTINUE TO QUICKLY ACCELERATE THE SYSTEM TO THE NORTHEAST AHEAD THE TROUGH AND DOES NOT BUILD THE RIDGE IN THE EXTENDED TAUS. THE JTWC FORECAST TRACK IS LAID CLOSE TO THE MULTI-MODEL CONSENSUS WITH OVERALL LOW CONFIDENCE DUE TO THE UNCERTAINTY ASSOCIATED WITH THE REBUILDING STR AND BIFURCATION IN THE MODELS.// NNNN