WDPN32 PGTW 150300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NAMTHEUN) WARNING NR 021// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 25.6N 160.0E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 337 NM EAST-NORTHEAST OF MINAMI TORI SHIMA MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 13 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A MEDIUM-SIZED SYSTEM WITH PERSISTENT DEEP CONVECTION CENTERING NEAR THE MAIN LOW-LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS EXTRAPOLATED WITH LOW CONFIDENCE BASED ON A 142040Z SSMIS 91GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY OF 40KTS IS PLACED WITH MEDIUM CONFIDENCE BASED ON AN OVERALL ASSESSMENT OF MULTIPLE AGENCIES, AUTOMATED DVORAK ESTIMATES (ADT), AND SATELLITE CONSENSUS (SATCON). ANALYSIS INDICATES A MARGINALLY FAVORABLE ENVIRONMENT WITH MODERATE POLEWARD AND EQUATORWARD OUTFLOW AND WARM SST OFFSET BY STRONG WESTERLY VWS. THE CYCLONE IS CONTINUING A TRACK ON THE POLEWARD SIDE OF THE STR TO THE SOUTH. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE SOUTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T3.0 - 45 KTS RCTP: T2.0 - 30 KTS KNES: T2.5 - 35 KTS CIMSS SATCON: 53 KTS AT 142309Z CIMSS ADT: 51 KTS AT 150110Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 25-30 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE POLEWARD AND EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: LOW 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: TS NAMTHEUN WILL CONTINUE ON ITS CURRENT TRACK UP TO TAU 24. AFTERWARD, A SECONDARY STR TO THE EAST WILL ASSUME STEERING AND DRIVE THE SYSTEM NORTHWARD, THEN ACCELERATE IT NORTHEASTWARD AFTER TAU 48. THE MARGINALLY FAVORABLE ENVIRONMENT WILL HOLD THE INTENSITY AT 40KTS FOR THE NEXT 12 HOURS. AFTERWARD, INCREASING VWS AND COOLING SSTS WILL BEGIN ERODING THE SYSTEM DOWN TO 30KTS BY TAU 48. CONCURRENTLY, THE CYCLONE WILL BEGIN TO UNDERGO EXTRA-TROPICAL TRANSITION (ETT) AS IT APPROACHES THE BAROCLINIC ZONE. BETWEEN TAU 48 AND 72, TS 23W WILL BECOME A MODERATE GALE-FORCE COLD-CORE LOW, COMPLETING ETT BY TAU 72. MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY TIGHT AGREEMENT, NAVGEM WAS UNAVAILABLE FOR THE MULTIPLE MODEL CONSENSUS. HOWEVER, WITH THE REMAINING MODELS, THERE IS ONLY A GRADUAL SPREAD AT THE WIDEST TO 100NM BY TAU 72, LENDING MEDIUM CONFIDENCE THROUGH TAU 72. THE ALONG TRACK UNCERTAINTY BETWEEN 48 AND 72 LENDS LOW CONFIDENCE DURING THIS 24 HOUR TIMEFRAME AS THE SYSTEM TRANSITIONS TO ETT. THERE IS ALSO MEDIUM CONFIDENCE IN THE INTENSITY FORECAST UP TO TAU 48, AND LOW THEREAFTER. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN