WDPN32 PGTW 310300 MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (MIRINAE) WARNING NR 21// RMKS/ 1. FOR METEOROLOGISTS. 2. 12 HOUR SUMMARY AND ANALYSIS. A. TROPICAL STORM 23W (MIRINAE), LOCATED APPROXIMATELY 55 NM SOUTHWEST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 15 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED AND MULTISPECTRAL SATELLITE IMAGERY SHOWS THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS QUICKLY PROGRESSED ACROSS THE CENTRAL PORTION OF LUZON, SOUTH OF MANIILA, IN THE PAST 06 HOURS. THE CURRENT POSITION HAS MIRINAE LOCATED IN THE SOUTH CHINA SEA (SCS), CONTINUING TO MOVE WESTWARD. THE LLCC APPEARS TO HAVE REMAINED INTACT, HOWEVER, THE CONVECTION OVER THE SYSTEM HAS BECOME DISORGANIZED WITH SPORADIC AREAS OF DEEP CONVECTION DEVELOPING WITHIN THE VICINITY OF THE LLCC. THE CURRENT INTENSITY IS SET AT 50 KNOTS BASED ON DVORAK VALUES FROM PGTW AND RJTD INDICATING A 55 KNOT INTENSITY AND ACCOUNTING FOR RECENT WEAKENING TRENDS OVER THE PAST 06 HOURS. 3. FORECAST REASONING. A. THE FORECAST REASONING HAS NOT CHANGED SIGNIFICANTLY SINCE THE PREVIOUS PROGNOSTIC REASONING BULLETIN, EXCEPT THE INTENSITIES HAVE BEEN DECREASED TO REFLECT THE WEAKENING TREND OBSERVED AS MIRINAE HAS TRACKED OVER LUZON. B. TY 23W HAS ENTERED INTO THE SCS AND IS EXPECTED TO CONTINUE TRACKING WESTWARD THROUGHOUT THE FORECAST PERIOD ALONG THE SOUTHERN PERIPHERY OF A STRONG SUBTROPICAL RIDGE TO THE NORTH. THE LLCC WILL BEGIN TO REORGANIZE IN THE NEXT 12 HOURS AS IT MOVES FURTHER INTO THE SCS. HOWEVER, VERTICAL WIND SHEAR (VWS) AND LOW- TO MID-LEVEL DRY AIR ENTRAINMENT FROM THE NORTHEASTERLY FLOW MOVING INTO THE SCS FROM A LOW- TO MID-LEVEL ANTICYCLONE LOCATED OVER NORTHERN PORTION OF THE KOREAN PENINSULA WILL PREVENT INTENSIFICATION BEYOND STRONG TROPICAL STORM STRENGTH. A SLIGHT INTENSITY INCREASE IS EXPECTED IN THE NEXT FEW HOURS AS THE SYSTEM REORGANIZES. AS MIRINAE APPROACHES CENTRAL VIETNAM, WITH LANDFALL EXPECTED AROUND TAU 48, INCREASED LAND INTERACTION AND STRONGER VWS WILL BEGIN TO WEAKEN THE SYSTEM, WITH FULL DISSIPATION EXPECTED BY TAU 72. MODEL GUIDANCE IS IN FAIR AGREEMENT WITH THE FORECAST SPEEDS, HOWEVER, THERE IS SOME DISAGREEMENT REGARDING THE LOCATION OF LANDFALL. PREDOMINANTLY THE MODELS EXPECT LANDFALL SOUTH OF QUI NHON, VIETNAM (APPROXIMATELY 13.8N), WITH THE MAJORITY OF THE MODELS CENTERED NEAR TUY HOA, VIETNAM (APPROXIMATELY 12.8N). THE CURRENT FORECAST FAVORS THE MAIN MODEL GROUPING SHOWING LANDFALL NEAR TUY HOA, VIETNAM.// NNNN