WDPN32 PGTW 131500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (CHANTHU) WARNING NR 030// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 31.0N 123.4E INITIAL INTENSITY: 65 KTS GEOGRAPHIC REFERENCE: 98 NM EAST OF SHANGHAI, CHINA MOVEMENT PAST 6 HOURS: NORTHWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 26 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TY 19W HAS RUN INTO A WALL OF RIDGING TO THE NORTH, AND FORWARD MOTION HAS COME TO A HALT OVER THE PAST SIX HOURS, AND THE LOW LEVEL CIRCULATION CENTER HAS STARTED TO DRIFT SLOWLY EASTWARD. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A DETERIORATING AND INCREASINGLY RAGGED CONVECTIVE CORE WITH WARMING CLOUD TOP TEMPERATURES. WHILE THERE IS NO EYE IN THE EIR, ANIMATED RADAR IMAGERY REVEALS A WEAK RADAR EYE FEATURE, WHICH LENT HIGH CONFIDENCE TO THE INITIAL POSITION. A 131045Z PARTIAL ASCAT-A PASS PROVIDED HIGH CONFIDENCE TO THE INITIAL WIND RADII, WHICH HAVE BEEN EXPANDED TO THE NORTHEAST AND DECREASED IN THE SOUTHWEST QUADRANT. THE INITIAL INTENSITY IS ASSESSED AT 65 KNOTS WITH MEDIUM CONFIDENCE, HEDGED LOWER THAN THE AGENCY CURRENT INTENSITY ESTIMATES IN LIGHT OF AN EXTREMELY LOW ADT FINAL-T, AND AGENCY DATA-T NUMBERS IN THE T3.5-T4.0 (55-65 KT) RANGE. THE ENVIRONMENT IS BECOMING INCREASINGLY MARGINAL WITH EACH PASSING HOUR, WITH PERSISTENT MODERATE SOUTHERLY VWS OFFSET BY ROBUST POLEWARD OUTFLOW AND MARGINAL SSTS. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: WEAK STEERING PATTERN BETWEEN SUBTROPICAL RIDGE (STR) TO THE WEST AND A SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS RJTD: T5.0 - 90 KTS KNES: T4.5 - 77 KTS CIMSS ADT: 49 KTS AT 131140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 15-20 KTS SST: 27-28 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING, HOWEVER THE FORECAST HAS BEEN SHORTENED TO 96 HOURS. FORECAST DISCUSSION: TY 19W HAS REACHED ITS PREDICTED POLEWARD LIMIT, AT LEAST FOR THE NEXT 48 HOURS, AS IT IS NOW ENTERED AN AREA OF WEAK STEERING FLOW BETWEEN COMPETING RIDGING EXTENDING FROM THE WEST ACROSS THE NORTH OF THE SYSTEM, AND A LARGE DEEP-LAYER STR TO THE EAST. WHILE THE EXACT TRACK OF TY 19W IS HIGHLY UNCERTAIN IN THE NEAR-TERM, IT IS EXPECTED TO MOVE EAST, THEN PERFORM A CLOCKWISE LOOP THROUGH TAU 48. BY TAU 48, THE WESTERN RIDGE WILL BEGIN TO ERODE AHEAD OF AN APPROACHING MID-LATITUDE DYNAMIC TROUGH WHILE THE STR TO THE EAST BUILDS AND REORIENTS TO THE SOUTHWEST-NORTHEAST ORIENTATION. BY TAU 72 THE TROUGH WILL EJECT TY 19W ONTO AN ACCELERATING TRACK TOWARDS CHEJU DO, SKIRTING THE SOUTH COAST OF KOREA AND INTO THE SEA OF JAPAN BY TAU 96. BY TAU 72 THE SYSTEM WILL BE MOVING IN PHASE WITH THE MID-LATITUDE TROUGH AND BEGIN TO INTERACT WITH THE BAROCLINIC ZONE OVER KOREA, AND COMMENCE EXTRATROPICAL TRANSITION (ETT). ETT IS EXPECTED TO BE COMPLETE BY TAU 120 AS THE SYSTEM DEVELOPS THERMAL ADVECTION AND EMBEDS WITHIN THE STRONG UPPER-LEVEL WESTERLIES. THE SYSTEM IS FORECAST TO STEADILY WEAKEN DUE TO A COMBINATION OF UPWELLING OF COOLER WATERS AND DECREASING OUTFLOW ALOFT, REACHING A MINIMUM OF 40 KNOTS BY TAU 72. THE SYSTEM WILL MAINTAIN 40 KNOT INTENSITY THROUGH ETT AS IT TAPS INTO THE ROBUST, DIVERGENT OUTFLOW AHEAD OF THE MID-LATITUDE TROUGH OFFSETTING THE INCREASING VWS AND DECREASING SSTS. MODEL DISCUSSION: TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT ON THE CLOCKWISE LOOP SCENARIO THROUGH TAU 48, WITH ALL TRACKERS OTHER THAN HWRF AND NAVGEM SUPPORTING THIS SOLUTION. THEREAFTER THE BULK OF THE GUIDANCE SUPPORTS THE TRACK TOWARDS THE NORTHEAST. WHILE CROSS-TRACK UNCERTAINTY REMAINS A RELATIVELY LOW 140NM AT TAU 96, ALONG-TRACK UNCERTAINTY INCREASES TO 400NM AT TAU 96, AS MODELS DISAGREE ON THE RATE OF ACCELERATION DURING THE ETT PHASE. CONFIDENCE IN THE FORECAST TRACK IS LOW THROUGH TAU 48 DUE TO THE LOW PREDICTABILITY OF THE LOOPING TRACK, AND IS LOW THROUGH TAU 96 DUE TO THE UNCERTAINTY OF THE TIMING OF THE BREAKOUT AND SUBSEQUENT TRACK SPEEDS DURING ETT. INTENSITY GUIDANCE IS MIXED, WITH THE GFS, TWRF AND HWRF INDICATING NEAR-TERM INTENSIFICATION, WHICH SEEMS HIGHLY UNLIKELY CONSIDERING THE ENVIRONMENT, WHILE THE REMAINDER OF THE MODELS SHOW EXTREMELY RAPID WEAKENING. THE JTWC FORECAST LIES CLOSE TO THE CONSENSUS MEAN AND DECAY SHIPS FOR THE DURATION OF THE FORECAST WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN