WDPN32 PGTW 160300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (CHANTHU) WARNING NR 040// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 30.4N 125.1E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 285 NM WEST-SOUTHWEST OF SASEBO, JAPAN MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 02 KTS SIGNIFICANT WAVE HEIGHT: 20 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TS 19W HAS TRACKED ERRATICALLY WITH A LOOP EVIDENT OVER THE PAST 24 HOURS AND HAS CONTINUED TO SLOWLY CONSOLIDATE. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) INDICATES TIGHTLY-CURVED BANDING WRAPPING INTO A DEFINED CENTER WITH A WEAK, DEVELOPING EYE EVIDENT. THIS IMPROVED CONVECTIVE STRUCTURE IS CLEARLY EVIDENT IN A 152202Z SSMIS 91GHZ MICROWAVE IMAGE. CONSEQUENTLY, DVORAK ESTIMATES HAVE INCREASED AND SUPPORT THE INITIAL INTENSITY ASSESSMENT WITH MEDIUM CONFIDENCE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE MSI AND THE RECENT SSMIS MICROWAVE IMAGE. POLEWARD OUTFLOW REMAINS ROBUST, WHICH IS AIDING THE RECENT INTENSIFICATION, AND VERTICAL WIND SHEAR REMAINS FAVORABLE AS WELL. SST VALUES REMAIN CONDUCIVE AT 28C. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE EXTENSION TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T3.0 - 45 KTS RCTP: T3.5 - 55 KTS KNES: T3.5 - 55 KTS CIMSS ADT: 49 KTS AT 152340Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH 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: TS 19W IS FORECAST TO TRACK NORTH-NORTHEASTWARD TO NORTHEASTWARD AS THE SUBTROPICAL RIDGE EXTENSION BUILDS INTO WESTERN JAPAN IN RESPONSE TO AN APPROACHING MIDLATITUDE RIDGE. THE SYSTEM WILL ACCELERATE EAST-NORTHEASTWARD AFTER TAU 24 AS STRONG WESTERLY FLOW DEVELOPS OVER SOUTH KOREA AND HONSHU. THERE IS A SHORT 12-HOUR WINDOW FOR FURTHER DEVELOPMENT WITH FAVORABLE ENVIRONMENTAL CONDITIONS THUS TS 19W IS FORECAST TO INTENSIFY SLIGHTLY TO 65 KNOTS BY TAU 12. AFTER TAU 12, VERTICAL WIND SHEAR (VWS) PRIOR TO LANDFALL NEAR TAU 30 WILL INCREASE STEADILY TO 20 TO 25 KNOTS, WHICH SUPPORTS A STEADY WEAKENING TREND AS THE SYSTEM APPROACHES NORTHWEST KYUSHU. INTERACTION WITH LAND AND SLIGHTLY COOLER SST VALUES WILL ALSO CONTRIBUTE TO THE WEAKENING TREND. BY TAU 24, SOUTH OF SOUTH KOREA, TS 19W WILL BEGIN TO INTERACT WITH THE BAROCLINIC ZONE AND JET, AND WILL WEAKEN TO 55 KNOTS AS IT BEGINS EXTRA-TROPICAL TRANSITION (ETT). TS 19W WILL CONTINUE TO TRACK ACROSS WESTERN JAPAN, WEAKEN FURTHER AND COMPLETE ETT BY TAU 48 NEAR CENTRAL HONSHU UNDER JET STRENGTH WESTERLIES. THE CENTER SHOULD BROADEN DURING THIS PHASE WITH DEEP CONVECTION DECAYING RAPIDLY. THE SYSTEM IS EXPECTED TO MAINTAIN GALE-FORCE WINDS, WHICH SHOULD BECOME HIGHLY ASYMMETRIC AS IT TRACKS NEAR THE TOKYO AREA. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT THROUGH TAU 36 WITH A 36NM SPREAD IN SOLUTIONS AT TAU 36. AFTER TAU 36, MODEL GUIDANCE DIVERGES AS THE SYSTEM GAINS FRONTAL CHARACTERISTICS AND THE EXACT CENTER POSITION BROADENS AND BECOMES INCREASINGLY UNCERTAIN. OVERALL, CONFIDENCE IN THE JTWC FORECAST TRACK IS MEDIUM WITH UNCERTAINTY IN THE RECURVE TIMING OVER THE NEXT 36 HOURS. THE JTWC FORECAST TRACK IS POSITIONED CLOSE TO THE JTWC MULTI-MODEL CONSENSUS (CONW). TS 19W APPEARS TO BE TRYING TO FORM AN EYE BUT CORE CONVECTION HAS CYCLED QUICKLY DIURNALLY THEREFORE THERE IS UNCERTAINTY IN THE PEAK INTENSITY OVER THE NEXT 12 HOURS. THUS THERE IS MEDIUM CONFIDENCE IN THE JTWC INTENSITY FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN