WDPN31 PGTW 242100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 10W (MA-ON) WARNING NR 014// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 20.4N 113.6E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 119 NM SOUTH-SOUTHWEST OF HONG KONG MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS SIGNIFICANT WAVE HEIGHT: 21 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM 10W (MA-ON) IS HOLDING TOGETHER WELL DESPITE TAKING A POUNDING FROM NORTHEASTERLY VERTICAL WINDSHEAR. WARM SEA WATERS AND HIGH OCEAN HEAT CONTENT ARE SUSTAINING THE LOW LEVEL VORTEX AND A SCATTEROMETRY PASS OVER THE EASTERN SEMICIRCLE AT 241355Z VERIFIES THE INTEGRITY OF THE LOW LEVEL CIRCULATION CENTER (LLCC) AND THE OVERALL SYSTEM INTENSITY. THE JTWC FIX AT T3.5 WAS ON A PARTLY EXPOSED LLCC AND IS IN LOCK-STEP WITH THE JMA, SUPPORTING THE CURRENT INTENSITY ASSESSMENT OF 55KTS. INITIAL WIND RADII BASIS: PERSISTENCE OVER THE WESTERN SEMICIRCLE AND A 241355Z SCATTEROMETRY PASS OVER THE EASTERN SEMICIRCLE. CURRENT STEERING MECHANISM: THE BOTTOM FLANK OF THE SUBTROPICAL RIDGE EXTENDING OVER EASTERN CHINA. THE RIDGE IS ANCHORED IN AN ANTICYCONE ALOFT DUE EAST OF TAIWAN AND DUE SOUTH OF OKINAWA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T3.5 - 55 KTS KNES: T3.5 - 55 KTS CIMSS ADT: 37 KTS AT 241740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 30+ KTS SST: 30-31 CELSIUS OUTFLOW: MODERATE EQUATORWARD OTHER FACTORS: THERE IS NO POLEWARD OUTFLOW DUE TO THE VIGOROUS NORTHEASTERLIES ALOFT. ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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: THE MID-LEVEL STEERING RIDGE ALOFT WILL DRIVE TROPICAL STORM MA-ON ALONG A STEADY WEST-NORTHWESTWARD BEARING AT A STEADY SPEED OF ADVANCE UNTIL IT DIES IN NORTHERN VIETNAM. ALONG THE WAY IT WILL CROSS THE EXTREME NORTHERN PART OF THE LUICHOW PENINSULA WITHOUT LOSING MUCH INTENSITY AND RE-GATHER ITSELF OVER THE EXTREMELY WARM WATERS OF THE GULF OF TONKIN. ALTHOUGH VERTICAL WINDSHEAR WILL GRADUALLY WEAR THE SYSTEM DOWN, IT WILL SURVIVE UNTIL IT HITS THE VIETNAMESE COAST. THE MOUNTAINOUS TERRAIN OF NORTHERN VIETNAM WILL TEAR THE SYSTEM APART WITHIN 15 HOURS OF MAKING LANDFALL, AND IT WILL BE HARD TO LOCATE THE VORTEX SOONER THAN THAT. MODEL DISCUSSION: MODEL GUIDANCE HAS BEEN EXCELLENT THROUGHOUT THE LIFECYCLE OF THIS STORM. THERE IS EXCELLENT MODEL AGREEMENT REGARDING BOTH TRACK AND INTENSITY AND THE SCENARIO OF WESTWARD MOVEMENT ONTO A LAND MASS IS SIMPLE. THEREFORE THE JWTC TRACK RIDES STRAIGHT ON TOP OF THE MULTI-MODEL CONSENSUS AND THE INTENISTY FORECAST STAYS NEAR THE MEAN UNTIL THE LAST POSITION, WHEN THE TERRAIN IS CONSIDERED AND THE FORECAST INTENSITY IS DROPPED BELOW GUIDANCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN