WDPN32 PGTW 120300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (CHANTHU) WARNING NR 024// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 23.8N 122.3E INITIAL INTENSITY: 110 KTS GEOGRAPHIC REFERENCE: 340 NM WEST-SOUTHWEST OF KADENA AB MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 45 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TY 19W CONTINUES TO EXPERIENCE A SERIES OF FAIRLY QUICK EYEWALL REPLACEMENT CYCLES (ERC) INCLUDING THE ONGOING ERC, WHICH IS EVIDENT IN AN 112300Z SSMIS 91GHZ COMPOSITE IMAGE. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY, ANIMATED RADAR IMAGERY AND THE 112300Z SSMIS 91GHZ IMAGE DEPICT A SMALL CORE OF INTENSE CONVECTION SURROUNDING A 6NM EYE WITH EXTENSIVE SPIRAL BANDING. AS OF 120200Z, TY 19W'S CENTER IS LOCATED ABOUT 25NM WEST OF YONAGUNIJIMA (47912), WHICH IS REPORTING 10-MINUTE SUSTAINED SURFACE WINDS AT 45 KNOTS WITH AN SLP VALUE OF 989.4MB. POLEWARD AND EQUATORWARD OUTFLOW HAVE REMAINED ROBUST WITH LOW VERTICAL WIND SHEAR (VWS) AND WARM SST. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON EIR IMAGERY. THE INITIAL INTENSITY OF 110 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW AND KNES DVORAK CURRENT INTENSITY ESTIMATES OF 5.5-6.0 AND THE ADT ESTIMATE. THE RJTD DATA-T IS AT A T6.0 (115 KNOTS) WHILE THE CURRENT INTENSITY REMAINS CONSERVATIVE AT 7.0 (140 KNOTS). INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: DEEP-LAYERED, NORTH-SOUTH ORIENTED SUBTROPICAL RIDGE (STR) ENTRENCHED TO THE EAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.0 - 115 KTS RJTD: T7.0 - 140 KTS KNES: T5.5 - 102 KTS CIMSS ADT: 107 KTS AT 120210Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THE SYSTEM IS NOW EXPECTED TO BEGIN EXTRA-TROPICAL TRANSITION AT TAU 120 NEAR CHEJU ISLAND. FORECAST DISCUSSION: TY 19W WILL TRACK POLEWARD ALONG THE WESTERN PERIPHERY OF THE STR THROUGH TAU 72. THE SYSTEM SHOULD STEADILY WEAKEN AS IT INTERACTS WITH TAIWAN AND UPPER-LEVEL DIVERGENCE DECREASES AS THE SYSTEM BEGINS TO INTERACT WITH AN UPPER-LEVEL SUBTROPICAL TROUGH EXPECTED TO DEEPEN OVER EASTERN CHINA OVER THE NEXT TWO DAYS. IN THE EXTENDED PERIOD, TY 19W IS FORECAST TO TRACK EAST-NORTHEASTWARD WITHIN WESTERLY FLOW AND WILL WEAKEN TO TS STRENGTH (40 KNOTS) BY TAU 120. NUMERICAL MODEL GUIDANCE INDICATES A FAIRLY ATYPICAL MIDLATITUDE PATTERN WITH WEAK TO MODERATE SUBTROPICAL WESTERLIES AND THE FRONTAL ZONE TO THE NORTH OVER THE KOREAN PENINSULA, THEREFORE, EXTRATROPICAL TRANSITION IS NOT EXPECTED UNTIL TAU 120 WHEN THE SYSTEM FIRST BEGINS TO INTERACT WITH THE BAROCLINIC ZONE. ADDITIONALLY, TRACK SPEEDS SHOULD BE UNUSUALLY SLOW THROUGH TAU 120. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT THROUGH TAU 48 WITH A 70NM SPREAD IN SOLUTIONS AT TAU 48. AFTER TAU 48, THERE IS INCREASING UNCERTAINTY WITH WEAKER STEERING FLOW THUS MEDIUM OVERALL TRACK CONFIDENCE. IN THE EXTENDED PERIOD, THERE IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST WITH LARGE SPREAD IN MODEL SOLUTIONS. CROSS-TRACK SPREAD IS ABOUT 150NM AT TAU 120 WITH THE GFS ENSEMBLE MEAN (GEFS) AND UKMET TRACKING INTO THE SYSTEM INTO NORTHERN KYUSHU WHILE THE BULK OF THE GUIDANCE IS OVER CHEJU ISLAND AND THE SOUTHERN PORTIONS OF SOUTH KOREA. ALONG-TRACK TRACK SPEEDS HAVE INCREASED REFLECTING THE STRONGER UPPER-LEVEL WESTERLY FLOW DEVELOPING AFTER TAU 96. THERE IS LOW CONFIDENCE IN THE JTWC INTENSITY FORECAST DUE TO THE COMPLEX INTERACTIONS WITH THE AFOREMENTIONED TROUGH AND SUBTROPICAL WESTERLIES AS WELL AS INTERACTION WITH TAIWAN AND EASTERN CHINA. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN