WDPN31 PGTW 130300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (KALMAEGI) WARNING NR 10// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 15W (KALMAEGI), LOCATED APPROXIMATELY 454 NM EAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY INDICATES A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC) WITH IMPROVED CORE CONVECTION ASSOCIATED WITH A CENTRAL DENSE OVERCAST FEATURE (CDO); ADDITIONALLY, CONVECTIVE BANDING HAS IMPROVED OVER THE WESTERN SEMI-CIRCLE OF THE SYSTEM. THE INITIAL INTENSITY IS ASSESSED AT 55 KNOTS BASED ON THE IMPROVED STRUCTURE AND DVORAK INTENSITY ESTIMATES OF 55 KNOTS. A 122356Z GMI IMAGE AND A 122252Z SSMIS IMAGE DEPICT MULTIPLE CONVECTIVE BANDS TIGHTLY WRAPPING INTO A WELL-DEFINED LLCC POSITIONED ON THE NORTH QUADRANT OF THE CDO, THEREFORE, THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION. DESPITE MODERATE NORTHEASTERLY VERTICAL WIND SHEAR (VWS), WHICH IS HINDERING DEEP CONVECTIVE DEVELOPMENT OVER THE NORTHERN SEMI-CIRCLE, THE OVERALL ENVIRONMENT IS FAVORABLE WITH IMPROVED OUTFLOW INTO A TUTT CELL LOCATED NEAR GUAM. ADDITIONALLY, THE MODERATE VWS IS BEING REDUCED BY THE WESTWARD TRACK MOTION AND OUTFLOW HAS A MORE RADIAL APPEARANCE IN THE ANIMATED WATER VAPOR IMAGERY. RECENT 500 MB ANALYSES SHOW A STRONG, EAST-WEST ORIENTED SUBTROPICAL RIDGE (STR) ENTRENCHED TO NORTH AND NORTHWEST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 15W IS FORECAST TO TRACK WEST-NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR. IN THE NEXT 24 HOURS, TS 15W IS EXPECTED TO MAINTAIN MODERATE TRACK SPEEDS (07 TO 09 KNOTS) AS IT TRANSITS SOUTH OF A BREAK IN THE STR. THEREAFTER, THE SYSTEM SHOULD ACCELERATE AS IT TRANSITIONS TO THE WESTERN BRANCH OF THE STR, WHICH IS FORECAST TO STRENGTHEN AS A MIDLATITUDE RIDGE BUILDS OVER EAST ASIA. TS 15W IS FORECAST TO RAPIDLY INTENSIFY THROUGH TAU 36 UNDER FAVORABLE ENVIRONMENTAL CONDITIONS TO INCLUDE WARM SST, HIGH OCEAN HEAT CONTENT AND FAVORABLE OUTFLOW. TS KALMAEGI IS FORECAST TO MAKE LANDFALL OVER EASTERN LUZON NEAR TAU 42, LEADING TO A TEMPORARY WEAKENING AS IT CROSSES THE MOUNTAINOUS TERRAIN OF LUZON. C. IN THE EXTENDED TAUS, TS 15W IS EXPECTED TO MAINTAIN A WEST- NORTHWESTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST PERIOD AS THE STR REMAINS ENTRENCHED TO THE NORTH. FAVORABLE ENVIRONMENTAL CONDITIONS IN THE SOUTH CHINA SEA (SCS) WILL FURTHER ALLOW TS 15W TO INTENSIFY AS IT TRACKS ACROSS THE NORTHERN SCS. NEAR TAU 96, TS KALMAEGI IS FORECAST TO WEAKEN AS IT APPROACHES THE SOUTHERN COAST OF CHINA. DYNAMIC MODEL GUIDANCE (INCLUDING THE MODEL ENSEMBLES) IS IN TIGHT AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK, WHICH IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS.// NNNN