WDPN31 PGTW 241500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 10W (MA-ON) WARNING NR 013// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 20.3N 115.3E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 135 NM SOUTH-SOUTHEAST OF HONG KONG MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS SIGNIFICANT WAVE HEIGHT: 21 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED SATELLITE IMAGERY INDICATES A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) POSITIONED ON THE NORTHERN EDGE OF A LARGE AREA OF PERSISTENT DEEP CONVECTION, WHICH IS SHEARING OVER THE SOUTHERN SEMICIRCLE DUE TO HIGH NORTHEASTERLY VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON A 240836Z SSMIS 91GHZ COLOR COMPOSITE MICROWAVE IMAGE, WHICH SHOWS SHALLOW BANDING WRAPPING INTO A PARTIALLY-OBSCURED LLCC WITH SPIRAL BANDING OVER THE SOUTHERN QUADRANT, AND A PARTIAL 241303Z ASCAT-B IMAGE. ENVIRONMENTAL CONDITIONS HAVE REMAINED MARGINAL WITH STRONG NORTHEASTERLY VWS OFFSET BY MODERATE EQUATORWARD OUTFLOW. THE INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW AND RJTD DVORAK ESTIMATES AND IS ALSO SUPPORTED BY THE ASCAT-B IMAGE SHOWING NUMEROUS 45-50 KNOT WINDS OVER THE EASTERN SEMICIRCLE. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTH AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T3.5 - 55 KTS KNES: T4.0 - 65 KTS CIMSS SATCON: 50 KTS AT 240922Z CIMSS ADT: 47 KTS AT 241140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 30+ KTS SST: 30-31 CELSIUS OUTFLOW: MODERATE EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 10W IS FORECAST TO TRACK WEST-NORTHWESTWARD TO WESTWARD THROUGH THE FORECAST PERIOD WITH LANDFALL EXPECTED NEAR TAU 18. TS 10W WILL GRADUALLY WEAKEN OVER THE NEXT 18 HOURS AS IT TRACKS UNDER HIGH NORTHEASTERLY VERTICAL WIND SHEAR. AFTER TAU 18, THE SYSTEM WILL RAPIDLY DISSIPATE AS IT TRACKS INLAND OVER THE RUGGED TERRAIN OF NORTHERN VIETNAM. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT WITH A 30-50NM SPREAD IN SOLUTIONS THROUGH THE FORECAST PERIOD, THEREFORE THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK. RELIABLE INTENSITY GUIDANCE IS IN GOOD AGREEMENT AND SUPPORTS THE JTWC INTENSITY FORECAST WITH HIGH CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: HIGH// NNNN