WDPN33 PGTW 252100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (NEPARTAK) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 32.9N 150.3E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 546 NM EAST-SOUTHEAST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTHWARD AT 11 KTS SIGNIFICANT WAVE HEIGHT: 13 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A CLASSIC SUBTROPICAL CYCLONE WITH A BROAD SWATH OF CONVECTION CURLING INTO A WIDE AND ELONGATED CIRCULATION WITH AT LEAST THREE EMBEDDED VORTICES. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE ON THE CENTROID OF THESE VORTICES. THE INITIAL INTENSITY OF 35KTS IS BASED ON PATCHES OF 35-KT WIND BARBS DEPICTED IN RECENT SCATTEROMETRY PASSES OVER 100NM AWAY FROM THE CENTROID AND UNDER THE SWATH OF CONVECTION. ALTHOUGH NOT REPRESENTATIVE OF THE STORM POSITION, THE INITIAL INTENSITY IS SUPPORTED BY THE PGTW DVORAK AND THE ADT AUTOMATED FIXES. INITIAL WIND RADII BASIS: PERSISTENCE, ADJUSTED FROM RECENT SCATTEROMETER DATA. CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS RCTP: T2.0 - 30 KTS CIMSS ADT: 35 KTS AT 251740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 30+ KTS SST: 26-27 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: LOW 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: SUBTROPICAL CYCLONE 11W WILL TRACK NORTHWESTWARD UNDER THE STEERING STR ON A PINWHEEL PATTERN AROUND AN UPPER LEVEL LOW TO THE SOUTHWEST, MAKING LANDFALL OVER NORTHERN HONSHU NEAR KASENNUMA, JAPAN, AROUND TAU 48. THE MARGINAL ENVIRONMENT - STRONG VWS OFFSET BY STRONG POLEWARD OUTFLOW AND WARM SST - WILL FUEL A SLIGHT INTENSIFICATION TO 40KTS AT TAUS 24-36. AFTERWARD, THE UPPER LEVEL WILL COME INTO PROXIMITY AND PROMOTE SUBSIDENCE ALOFT AND INDUCE THE INFLOW OF COLD DRY AIR IN THE LOWER LEVELS. THESE AND THE TOPOGRAPHICAL EFFECTS AFTER LANDFALL WILL ERODE THE SYSTEM DOWN TO 30KTS AFTER IT EXITS INTO THE SEA OF JAPAN (SOJ). THE COOLER SSTS IN THE SOJ PLUS A SECONDARY LANDFALL INTO HOKKAIDO AFTER THE SYSTEM RECURVES NORTHEASTWARD AROUND THE STR AXIS WILL FURTHER ERODE 11W TO DISSIPATION BY TAU 120. MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT WITH AEMN THE LEFT OUTLIER IN THE EXTENDED PERIOD CURLING THE VORTEX SOUTHWARD IN THE SOJ. GIVEN THE BROAD COMPLEXITY OF A SUBTROPICAL CYCLONE AND THE UNCERTAINTY OF A LAND PASSAGE, THERE IS MEDIUM CONFIDENCE IN THE JTWC TRACK AND INTENSITY FORECASTS UP TO TAU 72, THEN LOW CONFIDENCE AFTERWARD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN