WDXS31 PGTW 222100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (CHARLOTTE) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.8S 109.1E INITIAL INTENSITY: 80 KTS GEOGRAPHIC REFERENCE: 390 NM NORTHWEST OF LEARMONTH, AUSTRALIA MOVEMENT PAST 6 HOURS: SOUTHWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 28 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A MEDIUM-SIZED SYSTEM WITH DEEP CENTRAL CONVECTION REMAINING TO THE SOUTHERN EDGE OF THE LOW-LEVEL CIRCULATION (LLC). THE EIR LOOP ALSO INDICATES SUBSIDENCE CONTINUING TO REDUCE ALONG THE NORTHERN EDGES AND TRANSVERSE BANDING ENGULFING THE SOUTHWESTERN PERIPHERIES EXTENDING FROM THE CENTER OF THE SYSTEM TOWARDS DIRK HARTOG ISLAND, AUSTRALIA. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE EIR LOOP AND EXTRAPOLATION OF A PARTIAL 221441Z METOP-B ASCAT 25KM IMAGE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE OF 80KTS. THE MEDIUM CONFIDENCE IS BASED ON MULTIPLE AGENCY DVORAK FIXES INDICATING ARE ON THE DECLINE IN THE FINAL T ESTIMATES, BUT REMAIN HELD AT T5.0-90KTS BASED UPON CONSTRAINTS. OVER THE LAST 6 HOURS THE TREND FROM THE MULTIPLE AGENCIES HAS DECREASED TO INCLUDE THE ADVANCED DVORAK TECHNIQUE (ADT). ANALYSIS INDICATES A MARGINALLY UNFAVORABLE ENVIRONMENT WITH THE ROBUST POLEWARD OUTFLOW AND WARM SST OFFSET BY MODERATE TO STRONG VERTICAL WIND SHEAR. THE CYCLONE IS TRACKING ALONG THE NORTHWEST PERIPHERY OF THE STR TO THE SOUTHEAST. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: DEEP LAYER SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T5.0 - 90 KTS APRF: T5.0 - 90 KTS CIMSS ADT: 85 KTS AT 221840Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 20-25 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD 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: TC 21S CHARLOTTE WILL CONTINUE SOUTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR. THE SYSTEM IS CURRENTLY IN THE PROCESS OF ROUNDING THE STR AXIS AND WILL TRACK SOUTHWARD THEN SOUTHEASTWARD TOWARD PERTH, AUSTRALIA THROUGH THE REMAINDER OF THE FORECAST. THE ENVIRONMENT WILL REMAIN MARGINALLY UNFAVORABLE, AND BY TAU 60, TC CHARLOTTE WILL MOVE INTO A MORE UNFAVORABLE ENVIRONMENT WITH INCREASING VWS AND COOLING ALONG-TRACK SST. SHORTLY AFTER TAU 60 AND BEFORE TAU 72, TC 21S WILL BEGIN TRANSITIONING INTO A SUBTROPICAL SYSTEM AND COMPLETE THE TRANSITION AS A GALE FORCED SUBTROPICAL SYSTEM WITH AN EXPANDING WIND FIELD BY TAU 96. MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL FAIR AGREEMENT UNTIL TAU 72. ONCE THE SUBTROPICAL TRANSITION BEGINS, THE MODELING GUIDANCE BEGINS TO DIVERGE SIGNIFICANTLY WITH SEVERAL MODELS, INCLUDING AFUM, UKMET, EEMN, ECMF AND DEPICTS ERRATIC REVERSALS IN THE STORM MOTION. THE OVERALL JTWC TRACK AND INTENSITY GUIDANCE IS BASED ON MEDIUM CONFIDENCE NEAR TAU UP TO 72 AND LOW THEREAFTER. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN