WDPN31 PGTW 201500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (SANVU) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 9.7N 156.5E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 196 NM NORTH-NORTHWEST OF POHNPEI MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 18 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS IMPROVED CORE CONVECTIVE CONSOLIDATION WITH TWO PRIMARY PERSISTENT CONVECTIVE CELLS FULLY OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). AS WE FIND OURSELVES WITHOUT RECENT OR USABLE MICROWAVE IMAGERY, SCATTEROMETERY CAME TO THE RESCUE. A 201034Z ASCAT-B BULLSEYE SCATTEROMETERY PASS REVEALS A TIGHT AND ASYMMETRIC CIRCULATION WITH 30-40KT WINDS DOMINATING THE NORTHERN SEMICIRCLE WHILE 5-20KT WINDS EXIST IN THE SOUTHERN SEMICIRCLE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON EIR IMAGERY AND SCATTEROMETRY DATA. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON SCATTEROMERTY DATA. DVORAK INTENSITY ESTIMATES (T2.0-2.5), THOUGH NOT FAR BEHIND THE SCATTEROMETRY DATA, THESE ESTIMATES TYPICALLY DO NOT HANDLE SMALL SYSTEMS WELL AND SO THEIR VERACITY SHOULD BE TAKEN WITH A GRAIN OF SALT. CIMMS OPEN-AIR SEEMS TO BE RIGHT ON WITH THE JTWC CURRENT INTENSITY OF 40KTS WHILE CIMSS ADT MAINTAINS ITS AGGRESSIVE POSTURE, SHOWING 53KTS. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) TO THE EAST-NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS KNES: T2.5 - 35 KTS CIMSS ADT: 53 KTS AT 201130Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 5-10 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 01W (SANVU) IS FORECAST TO CONTINUE ITS GRADUAL WESTWARD COURSE CHANGE AS THE NER TO THE EAST IS GRADUALLY REPLACED AS THE PRIMARY STEERING FEATURE BY A BUILDING SUB-TROPICAL RIDGE (STR) TO THE NORTH. NOW IN A MARGINAL ENVIRONMENT CHARACTERIZED BY WARM SST AND RADIAL OUTFLOW ALOFT OFFSET BY BUILDING MID-LEVEL VERTICAL WIND SHEAR (VWS), 01W IS FORECAST TO GENERALLY STAGNATE NEAR 40KTS AND POSSIBLY A BIT HIGHER OVER THE NEXT 12 HOURS. BY TAU 12 AND THROUGH TAU 24, VWS WILL CONTINUE TO INCREASE AS THE BUILDING STR TO THE NORTH BEGINS TO ENTRAIN DRY AIR INTO THE SYSTEM RESULTING IN GRADUAL WEAKENING. AFTER TAU 24, 01W WILL CONTINUE TO WEAKEN AS IT TRACKS GENERALLY WEST-NORTHWESTWARD AND EVENTUALLY WESTWARD, ULTIMATELY DISSIPATING BY TAU 96. MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIR AGREEMENT THAT 01W WILL CONTINUE ITS GRADUAL WESTWARD TURN THROUGH THE FORECAST PERIOD WITH VARIOUS MEMBERS INDICATING SOME CROSS TRACK VARIATION. NVGM AND GFS ARE GROUPED WELL POLEWARD OF THE MULTI-MODEL CONSENSUS BY TAU 72 WHILE COAMPS-TC, HWRF AND ECMWF ARE EQUATORWARD OF THE CONSENSUS TRACK, AS VARIOUS MEMBERS ATTEMPT TO RESOLVE THE BUILDING STR TO THE NORTH. FOR THESE REASONS THE JTWC FORECAST TRACK IS PLACED CLOSE TO AND JUST EQUATORWARD OF THE MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE. RELIABLE MODEL INTENSITY GUIDANCE IS IN FAIR AGREEMENT WITH DECAY-SHIPS A CLEAR OUTLIER, INDICATING CONTINUED INTENSIFICATION THOUGH TAU 48 WHILE THE REMAINING MEMBERS SHOW NEGLIGIBLE WEAKENING OR BRIEF INTENSIFICATION THROUGH TAU 12, AFTER WHICH ALL MEMBERS EXCEPT DECAY-SHIPS SHOW WEAKENING THROUGH THE FORECAST PERIOD. FOR THESE REASONS THE JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN