MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (KALMAEGI) WARNING NR 21// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON 15W (KALMAEGI), LOCATED APPROXIMATELY 204 NM SOUTH OF HONG KONG, HAS TRACKED WEST-NORTHWESTWARD AT 17 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS IMPROVING CURVED CONVECTIVE BANDING WRAPPING TOWARDS THE LOW LEVEL CIRCULATION CENTER (LLCC). CONVECTION ALONG THE NORTHERN HALF OF THE SYSTEM HAS BEEN STRUGGLING TO RE-BUILD OVER THE PAST 12 HOURS, BUT IN RECENT IMAGERY, THE BAND ALONG THE NORTHERN PERIPHERY HAS SHOWN MARGINAL IMPROVEMENT. UPPER LEVEL ANALYSIS INDICATES A WEAK POINT-SOURCE ANTI- CYCLONE IS LOCATED OVER THE LLCC, PROVIDING GOOD RADIAL OUTFLOW IN A LOW VERTICAL WIND SHEAR ENVIRONMENT. TY 15W CONTINUES TO TRACK QUICKLY WESTWARD ALONG THE SOUTHERN PERIPHERY OF A DEEP LAYERED SUB- TROPICAL RIDGE (STR). 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 15W IS FORECAST TO REMAIN ON A QUICK TRACK TO THE WEST- NORTHWEST UNDER THE STEERING INFLUENCE OF THE STRONG STR THROUGHOUT THE FORECAST. AS TY 15W PASSES OVER HAINAN ISLAND, A STEADY WEAKENING TREND, INFLUENCED BY LAND INTERACTION, WILL BEGIN. LANDFALL IN NORTHERN VIETNAM WITHIN THE NEXT 24 HOURS WILL LEAD TO A RAPID DIS- SIPATION OF THE LLCC BY TAU 48. 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 NNNN