WDPN31 PGTW 120900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (WUTIP) WARNING NR 008// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.2N 109.9E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 117 NM NORTHEAST OF DA NANG, VIETNAM MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 20 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL STORM 01W (WUTIP) WITH EXPOSED LOW-LEVEL CLOUD LINES TIGHTLY WRAPPING INTO AN OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC) SOUTH OF HAINAN. 120540Z AMSR2 MICROWAVE IMAGES REVEALED THAT THE LLCC IS OFFSET SLIGHTLY TO THE NORTHEAST OF THE BULK OF CONVECTION. ENVIRONMENTAL ANALYSIS INDICATES THAT 01W IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE EQUATORWARD OUTFLOW ALOFT, MODERATE (15-20 KTS) EAST-NORTHEASTERLY VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE 120540Z AMSR2 37 GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE 120229Z METOP-B ASCAT PASS SHOWING A PATCH OF 45 KNOT SOUTHWESTERLIES WITHIN THE SOUTHERN SEMICIRCLE. ADDITIONALLY, A MAJORITY OF AGENCY DVORAK FIXES OF T3.0 SUPPORT THE INITIAL INTENSITY ASSESSMENT. CIMSS OBJECTIVE INTENSITY ESTIMATES ARE A BIT LOWER, HOVERING AROUND 37-41 KTS. INITIAL WIND RADII BASIS: 120229Z METOP-B SCATTEROMETER DATA CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T2.5 - 35 KTS RCTP: T3.0 - 45 KTS KNES: T3.0 - 45 KTS CIMSS ADT: 37 KTS AT 120600Z CIMSS AIDT: 37 KTS AT 120600Z CIMSS DPRINT: 41 KTS AT 120600Z CIMSS DMINT: 40 KTS AT 120543Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 15-20 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: 01W IS FORECAST TO TRACK NORTHWESTWARD THROUGH TAU 12 BEFORE BEGINNING TO ROUND THE RIDGE AXIS WITH A NORTHWARD TURN. AN INITIAL LANDFALL, JUST AFTER TAU 12, IS FORECAST TO OCCUR ALONG THE SOUTHWESTERN COAST OF HAINAN. NEAR TAU 24, THE SYSTEM WILL BEGIN TO TURN NORTHWESTWARD AND TRACK TOWARD THE LEIZHOU PENINSULA. 01W IS THEN FORECAST TO MAKE A SECOND LANDFALL NEAR TAU 48 AND CONTINUE ON A NORTHWESTWARD TRACK FURTHER INLAND THROUGH TAU 72 AS THE VORTEX DISSIPATES NORTH OF HONG KONG. 01W IS FORECAST TO MAINTAIN ITS CURRENT INTENSITY OF 50 KTS THROUGH TAU 24 DUE TO THE MOSTLY FAVORABLE ENVIRONMENT BEFORE LANDFALL. AFTER TAU 24, TERRAIN INTERACTION WITH HAINAN WILL WEAKEN THE VORTEX AS IT APPROACHES THE COAST OF CHINA. AFTER TAU 48, SIGNIFICANT TERRAIN INTERACTION WITH MAINLAND CHINA WILL CAUSE 01W TO QUICKLY WEAKEN AND DISSIPATE BY TAU 72. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT WITH A MERE 35 NM CROSS-TRACK SPREAD AND 50 NM ALONG-TRACK SPREAD AT TAU 48. AT TAU 72, ALONG-TRACK SPREAD INCREASES TO 230 NM DUE TO THE WEAK NATURE OF THE VORTEX AND RAPID DISSIPATION. OVERALL, THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE, CLOSE TO THE MULTI-MODEL CONSENSUS. INTENSITY GUIDANCE IS IN MODERATE AGREEMENT, WITH MODELS RANGING FROM 40-50 KTS THROUGH TAU 48 AND THEN AGREE ON RAPID WEAKENING AFTERWARD. THE JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM CONFIDENCE AS A RESULT. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN