WDPN31 PGTW 181500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (KOPPU) WARNING NR 23// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 24W (KOPPU), LOCATED APPROXIMATELY 125 NM NORTH- NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS A DISORGANIZED SYSTEM THAT APPEARS TO HAVE MOVED BACK OVER WATER; HOWEVER, THERE IS LOW CONFIDENCE IN THE INITIAL POSITION. THE CURRENT INTENSITY HAS BEEN DECREASED BASED ON THE CONTINUED DETERIORATION OF THE CLOUD SYSTEM STRUCTURE DUE TO THE LAND INTERACTION OVER LUZON. THE TYPHOON IS NOW ENCOUNTERING 20 TO 25 KNOT EASTERLY VERTICAL WIND SHEAR (VWS) THAT IS BEING PARTLY OFFSET BY STRONG DIVERGENT OUTFLOW. TY 24W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF AN EXTENSION OF THE DEEP-LAYERED SUB-TROPICAL RIDGE (STR) TO THE NORTHEAST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 24W WILL TRACK SLIGHTLY POLEWARD OVER THE NEXT 24 HOURS BEFORE A NEAR EQUATORIAL RIDGE BUILDS SOUTH OF THE SYSTEM, DRIVING IT EASTWARD THROUGH TAU 72. TY KOPPU WILL CONTINUE TO WEAKEN DUE TO LAND INTERACTION AS IT MOVES ALONG THE WESTERN COAST OF LUZON. NEAR TAU 72, TY KOPPU WILL RE-EMERGE OVER WATER IN THE LUZON STRAIT AT TROPICAL STORM INTENSITY. C. IN THE EXTENDED TAUS, TY KOPPU WILL TURN NORTHWARD AND THEN NORTHWESTWARD DUE TO A BUILDING STR TO THE NORTHEAST. THE TYPHOON WILL BEGIN TO RE-INTENSIFY AS THE SYSTEM ENCOUNTERS LOW VWS, GOOD OUTFLOW, AND WARM SSTS. DYNAMIC MODEL GUIDANCE CONTINUES TO SHOW A WIDE SPREAD AND A BIFURCATION DUE TO THEIR DEPICTION OF THE BUILDING STR WITH GFS, COAMPS-TC, AND HWRF TRACKING THE SYSTEM WESTWARD TOWARDS HONG KONG AND THE REMAINING BULK OF GUIDANCE TRACKING THE SYSTEM CLOSER TO TAIWAN. DUE TO THE CONTINUED SPREAD IN MODEL SOLUTIONS AND THE COMPLEX STEERING ENVIRONMENT, THERE IS OVERALL LOW CONFIDENCE IN THE JTWC FORECAST TRACK WHICH IS POSITIONED NEAR THE MULTI-MODEL CONSENSUS.// NNNN