WDPN31 PGTW 242100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 06W (CHAMPI) WARNING NR 016// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 20.3N 139.6E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 286 NM SOUTH-SOUTHWEST OF IWO TO MOVEMENT PAST 6 HOURS: NORTHWARD AT 05 KTS SIGNIFICANT WAVE HEIGHT: 18 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS MORE EXPANSIVE BUT ASYMMETRIC CONVECTION AROUND THE LOW-LEVEL CENTER (LLC), WITH A VORTICAL HOT TOWER CONTAINING CLOUD TOP TEMPERATURES COLDER THAN -80 DEGREES CELSIUS RECENTLY OBSERVED JUST SOUTHEAST OF THE ESTIMATED CENTER POSITION. THE MOST RECENT 241619Z AMSR2 MICROWAVE PASS INDICATED THAT A COMPLETE INNER CORE HAS NOT YET FORMED, WITH THE PRIMARY BAND WRAPPING ONLY ABOUT HALFWAY AROUND THE LLC. HIMAWARI-8 7.3 MICROMETER IMAGERY INDICATES THAT THE DRY AIR MASS TO THE SOUTHWEST IS MORE DISTANT FROM THE LLC THAN 12-24 HOURS AGO, BUT STILL CLOSE ENOUGH TO GET PERIODICALLY ENTRAINED INTO THE STORM'S CORE, LIKELY EXPLAINING THE STILL ASYMMETRIC DISTRIBUTION OF CONVECTION. HOWEVER, AN IMPROVING CLOUD PATTERN AND EXPANDING CONVECTIVE COVERAGE DURING THE PAST 6 HOURS HAS LEAD TO AN INCREASE IN AGENCY DVORAK INTENSITY ESTIMATES. THE CURRENT INTENSITY IS THUS RAISED TO 55 KT. VERTICAL WIND SHEAR REMAINS LOW, AND UPPER-LEVEL OUTFLOW IS OBSERVED IN ALL QUADRANTS. THIS OUTFLOW IS STILL RELATIVELY RESTRICTED, THOUGH A SHORTWAVE TROUGH CURRENTLY CROSSING THE RYUKYU ISLANDS MAY BRIEFLY OPEN UP A POLEWARD OUTFLOW CHANNEL DURING THE NEXT 24 HOURS. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T3.5 - 55 KTS KNES: T4.0 - 65 KTS CIMSS SATCON: 53 KTS AT 241627Z CIMSS ADT: 49 KTS AT 241740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE RADIAL OTHER FACTORS: DRY AIR MASS IN PROXIMITY TO THE SOUTHWEST ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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: DURING THE NEXT 36 HOURS, VERTICAL SHEAR IS EXPECTED TO REMAIN UNDER 15 KT, WHICH SHOULD ALLOW INNER CORE DEVELOPMENT TO CONTINUE. THE JTWC INTENSITY FORECAST THUS CALLS FOR STEADY, THOUGH NOT RAPID INTENSIFICATION TO A PEAK OF 75 KT IN 36-48 HOURS, JUST ABOVE SHIPS AND COAMPS-TC GUIDANCE AS THE CYCLONE TRACKS WEST OF IWO TO. LINGERING ENVIRONMENTAL DRY AIR IS EXPECTED TO REMAIN A MODERATING INFLUENCE ON THE INTENSIFICATION RATE. BEGINNING AROUND 36 HOURS, NORTHERLY SHEAR MAY ALSO BECOME A LIMITATION AS AN UPPER-LEVEL RIDGE NOSES IN FROM THE WEST. THE HWRF MODEL CONTINUES TO SUGGEST THAT MORE RAPID INTENSIFICATION TO 90-95 KT IS A POSSIBILITY, BUT IT IS WORTH NOTING THAT HWRF HAS BEEN CONSISTENTLY TOO AGGRESSIVE WITH SHORT-TERM DEVELOPMENT IN THE LAST SEVERAL RUNS. NONETHELESS, TROPICAL STORM (TS) 06W REMAINS COMPACT, AND THUS FORMATION OF A COHERENT EYEWALL COULD LEAD TO QUICKER INTENSIFICATION THAN FORECAST. THE RAPID INTENSIFICATION PREDICTION AID (RIPA) NOW GIVES A 52 PERCENT PROBABILITY OF RAPID INTENSIFICATION DURING THE NEXT 24 HOURS. BEYOND 48 HOURS, TS 06W WILL MOVE OVER RAPIDLY COOLER WATER (SST LESS THAN 26 DEGREES CELSIUS), WHICH WILL INDUCE STEADY WEAKENING AS THE CYCLONE MERGES WITH THE BAIU FRONTAL BOUNDARY TO THE SOUTHEAST OF HONSHU. THIS EVOLUTION WILL INDUCE TRANSITION INTO AN EXTRATROPICAL CYCLONE BETWEEN 72 AND 96 HOURS. THERE REMAINS MEDIUM CONFIDENCE IN THE TRACK FORECAST, AS A WEAK, NONTROPICAL CYCLONE FORMING WITHIN THE BAIU BOUNDARY MAY INTERACT SLIGHTLY WITH TS 06W DURING THE 48-72 HOUR PERIOD. SENSITIVITY TO THIS INTERACTION IS INDUCING SPREAD OF NEARLY 200 NM IN NUMERICAL MODEL GUIDANCE AT 72 HOURS. MODEL DISCUSSION: THE JTWC TRACK FORECAST IS SLIGHTLY SLOWER THAN THE PREVIOUS FORECAST AND SLIGHTLY TO THE RIGHT OF THE MULTI-MODEL CONSENSUS DUE TO THE LEFTWARD AND SLOW OUTLIER JGSM. THE JTWC INTENSITY FORECAST IS JUST ABOVE SHIPS AND COAMPS-TC THROUGH 36 HOURS, BUT JUST BELOW THE MULTI-MODEL CONSENSUS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN