WDPN33 PGTW 120300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (KOMPASU) WARNING NR 008// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.8N 119.2E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 272 NM NORTH-NORTHWEST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WESTWARD AT 12 KTS SIGNIFICANT WAVE HEIGHT: 18 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE BROAD EXTENT OF TS 24W, WITH SPIRAL BANDS EXTENDING FROM THE TAIWAN STRAIT IN THE NORTH TO SOUTHERN LUZON IN THE SOUTH. WHILE THE SYSTEM IS OVERALL QUITE LARGE, THE INNER CORE IS RELATIVELY SMALL. HAVING MOVED OFF TO THE WEST OF LUZON, THE EASTERN SIDE OF THE CIRCULATION HAS STRENGTHENED AND THE CORE HAS BECOME MORE SYMMETRICAL. HOWEVER, THE MSI AND ENHANCED INFRARED IMAGERY SHOW THAT CORE CONVECTION HAS DECREASED SIGNIFICANTLY OVER THE PAST SIX HOURS. A 112308Z SSMIS 91GHZ MICROWAVE IMAGE SHOWED A WELL-DEFINED BAND OF HEAVY CONVECTION TO THE SOUTHWEST OF LUZON, WEAK SPIRAL BANDS WITHIN THE CORE, BUT LITTLE TO NO DEEP CONVECTION IN THE NORTHEAST QUADRANT OF THE SYSTEM. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A SPIRAL BAND ANALYSIS OF THE AFOREMENTIONED MICROWAVE IMAGE. THE INITIAL INTENSITY OF 55 KNOTS IS ALSO ASSESSED WITH HIGH CONFIDENCE BASED ON AN AGREEMENT ACROSS ALL OBJECTIVE AND SUBJECTIVE DVORAK CURRENT INTENSITY ESTIMATES. THE ENVIRONMENT IS OVERALL MARGINALLY FAVORABLE, WITH WARM SSTS AND STRONG EQUATORWARD AND MODERATE POLEWARD OUTFLOW BEING OFFSET BY MODERATE EASTERLY VERTICAL WIND SHEAR. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) OVER CENTRAL CHINA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T3.5 - 55 KTS KNES: T3.5 - 55 KTS CIMSS ADT: 55 KTS AT 112340Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG EQUATORWARD OTHER FACTORS: MODERATE POLEWARD OUTFLOW. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL STORM KOMPASU IS FORECAST TO CONTINUE TRACKING NEARLY DUE WEST THROUGH THE FORECAST PERIOD, ALONG THE SOUTHERN PERIPHERY OF THE DEEP STR LYING OVER CENTRAL CHINA. THE SYSTEM IS EXPECTED TO MAKE ITS FIRST LANDFALL ALONG THE COAST OF CENTRAL HAINAN ISLAND NEAR TAU 36, EMERGE INTO THE GULF OF TONKIN BY TAU 48, THEN MAKE A SECOND LANDFALL ALONG THE COAST OF NORTH VIETNAM NEAR TAU 72. THE GENERAL ENVIRONMENT IS EXPECTED TO REMAIN MARGINALLY FAVORABLE FOR ANOTHER 12 TO 18 HOURS, WITH SHEAR VALUES REMAINING AT OR BELOW CURRENT LEVELS. IN RESPONSE, TS 24W IS FORECAST TO INTENSIFY TO 60 KNOTS BY TAU 12. AFTER TAU 12, THE SYSTEM WILL WEAKEN STEADILY UNDER INCREASING VWS. AFTER CROSSING HAINAN, THE SYSTEM IS EXPECTED TO EMERGE INTO THE GULF OF TONKIN AS A WEAK TROPICAL STORM, AND THE COMBINATION OF WEAK OUTFLOW AND MODERATE LEVELS OF VWS WILL PRECLUDE ADDITIONAL INTENSIFICATION BEFORE THE SECOND LANDFALL. ONCE ASHORE, FRICTIONAL EFFECTS WITH THE RUGGED TERRAIN OF VIETNAM WILL RAPIDLY ERODE THE CIRCULATION, LEADING TO DISSIPATION OVER NORTHERN LAOS NO LATER THAN TAU 120. MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT WITH MINIMAL SPREAD OF 75NM AT FIRST LANDFALL, INCREASING TO A MODEST 95NM AT SECOND LANDFALL. THE JTWC TRACK REMAINS CONSISTENT WITH THE PREVIOUS FORECAST AND JUST SLIGHTLY NORTH OF THE CONSENSUS MEAN, WITH HIGH CONFIDENCE. LIKEWISE, INTENSITY GUIDANCE IS IN GOOD AGREEMENT AND THE JTWC FORECAST LIES CLOSE TO THE CONSENSUS MEAN, THOUGH SLIGHTLY LOWER THAN THE CONSENSUS MEAN, ESPECIALLY AFTER THE FIRST LANDFALL, WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN