WDPN33 PGTW 142100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (TWENTYTHREE) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.8N 127.6E INITIAL INTENSITY: 25 KTS GEOGRAPHIC REFERENCE: 455 NM NORTHEAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 13 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH DEEP CONVECTIVE BANDING OVER THE WESTERN PERIPHERY WRAPPING INTO AND OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON AN EARLIER PARTIAL 141259Z ASCAT-C IMAGE, WHICH SHOWS AN ELONGATED BUT DEFINED CENTER WITH 20-25 KNOT WINDS OVER THE NORTHERN PERIPHERY. THE INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PGTW, RJTD DVORAK ESTIMATES OF T1.5 AND ASCAT DATA. ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE WITH MODERATE POLEWARD OUTFLOW, WARM (29-30C) SEA SURFACE TEMPERATURES (SSTS), AND MODERATE (10-15KTS) VERTICAL WIND SHEAR (VWS). INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.5 - 25 KTS FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: HIGH INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TD 23W IS TRACKING WESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST, AND WILL GRADUALLY TURN WEST-NORTHWESTWARD THOUGH TAU 24. THE STR IS EXPECTED TO STRENGTHEN TO THE NORTHEAST AND REALIGN TO A NORTHWEST-SOUTHEAST ORIENTATION WHICH WILL TURN THE SYSTEM NORTHWESTWARD THROUGH TAU 48. A DEEP MIDLATITUDE SHORTWAVE TROUGH WILL DIG OVER EASTERN CHINA BY TAU 48, WHICH WILL ALSO HELP STEER THE SYSTEM IN A NORTHWEST DIRECTION PASSING JUST NORTH OF LUZON. AFTER TAU 72, AS THE SHORTWAVE TRANSITS EASTWARD, A DEEP LAYER RIDGE OVER EAST CHINA WILL THEN BECOME THE MAIN STEERING FEATURE WHICH WILL ALSO INDUCE A NORTHEASTERLY SURGE EVENT. THIS WILL RESULT IN THE SYSTEM TRACKING SOUTHWESTWARD THEN WEST-SOUTHWESTWARD THROUGH THE REMAINED OF THE FORECAST. TD 23W WILL STEADILY INTENSIFY THROUGH TAU 36 WITH RAPID INTENSIFICATION POSSIBLE BETWEEN TAU 36 TO TAU 72, AS POLEWARD OUTFLOW IMPROVES BY ENHANCED UPPER LEVEL WESTERLIES WHILE THE SYSTEM TRACKS OVER WARM (29-30C) SSTS AND HIGH OCEAN HEAT CONTENT. BETWEEN TAU 96 AND TAU 120, THE NORTHEASTERLY SURGE EVENT WILL INCREASE VERTICAL WIND SHEAR (VWS) WHILE INCREASING DRY AIR AROUND THE SYSTEM WHICH WILL RESULT IN STEADY WEAKENING THROUGH THE END OF THE FORECAST. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT THROUGH THE FORECAST PERIOD WITH A LARGE SPREAD OF 150-200NM FROM TAU 72 TO TAU 120. THROUGH TAU 48 BOTH THE AVNI AND AEMI TRACKERS ARE VERY CLOSE TO THE NORTHERN EDGE OF LUZON, BEFORE FOLLOWING CLOSE TO THE MULTI-MODEL CONSENSUS THROUGH TAU 120. ADDITIONALLY, BETWEEN TAU 96 AND TAU 120 THE PRIMARY OUTLIERS ARE JGSM ON THE SOUTHERN EDGE OF THE AIDS ENVELOPE, AND NVGM ON THE NORTHERN EDGE. THE BULK OF THE ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS) SOLUTIONS SUPPORT THE JTWC FORECAST TRACK THROUGH TAU 48, WITH INCREASING UNCERTAINLY AFTER TAU 72. THEREFORE, THE JTWC FORECAST TRACK IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE. THE RELIABLE INTENSITY GUIDANCE IS IN FAIR AGREEMENT AND SUPPORTS AN INTENSIFICATION PHASE WITH HWRF INDICATING A PEAK INTENSITY NEAR 85 KNOTS AND COAMPS-TC (NAVGEM VERSION) A PEAK INTENSITY OF 95 KNOTS, ABOVE THE INTENSITY CONSENSUS PEAK OF 80 KNOTS. GEFS INDICATES HIGH PROBABILITY OF MODERATE INTENSIFICATION AND A 10 PERCENT CHANCE OF RAPID INTENSIFICATION (RI) BETWEEN TAU 48 AND TAU 72. AFTER TAU 72 THE INTENSITY GUIDANCE INCREASES IN UNCERTAINTY DUE TO HOW THE SYSTEM INTERACTS WITH THE MODERATE NORTHEAST SURGE EVENT. THEREFORE, THE JTWC FORECAST INTENSITY IS PLACED WITH LOW CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN