WDPN31 PGTW 172100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (SIXTEEN) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.2N 110.0E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 99 NM EAST OF DA NANG, VIETNAM MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING DEEP CONVECTIVE BURSTS OVER THE WEST AND NORTHWEST PERIPHERY OF A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON A 171425Z ASCAT-C BULLSEYE IMAGE AND ANIMATED PROXYVIS SATELLITE IMAGERY. THE ASCAT-C IMAGE SHOWS A SWATH OF 25 TO 30 KNOT WINDS OVER THE SOUTHERN AND EASTERN QUADRANTS. UNFORTUNATELY, THERE ARE NO USEFUL SURFACE OBSERVATIONS AT THIS TIME AND MICROWAVE IMAGERY HAS BEEN SPARSE OVER THE PAST SIX HOURS. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON RECENT ASCAT DATA AND THE RECENT ADT, AIDT AND DPRINT OBJECTIVE DVORAK ESTIMATES. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: LOW-LEVEL REFLECTION OF THE SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST AND NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.5 - 25 KTS KNES: T1.5 - 25 KTS CIMSS ADT: 28 KTS AT 171730Z CIMSS AIDT: 29 KTS AT 171730Z CIMSS DPRINT: 32 KTS AT 171800Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 5-10 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: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TD 16W IS FORECAST TO TRACK GENERALLY NORTH- NORTHWESTWARD THROUGH TAU 48 ALONG THE WESTERN PERIPHERY OF THE LOW- LEVEL STR. THE SYSTEM IS EXPECTED TO MAINTAIN TD STRENGTH THROUGH TAU 24 WITH SLIGHT INTENSIFICATION AFTER THE SYSTEM TRACKS PAST HAINAN ISLAND NEAR TAU 36. AFTER TAU 48, A WEAK STR IS EXPECTED TO BUILD TO THE NORTH AND NORTHWEST EFFECTIVELY BLOCKING POLEWARD PROGRESSION AND PRODUCING A PROLONGED PERIOD OF SLOW, QUASI-STATIONARY TRACK MOTION NORTHWEST OF HAINAN ISLAND. BY TAU 72, THE SYSTEM WILL INTENSIFY TO ABOUT 40 TO 45 KNOTS DUE TO MODERATE POLEWARD OUTFLOW AND WARM SST. AFTER TAU 72, THE SYSTEM WILL LIKELY DRIFT SOUTHWARD WHILE WEAKENING DUE TO DRY AIR ENTRAINMENT AND WEAK DIVERGENCE ALOFT. MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 36 THEN FAIR AGREEMENT THROUGH TAU 72 THUS THERE IS MEDIUM OVERALL CONFIDENCE IN THE JTWC TRACK FORECAST THROUGH TAU 72. THE 171200Z COAMPS-TC ENSEMBLE (CTCXEPS) INTENSITY PROBABILITY CHART SHOWS A 60 TO 70 PERCENT PROBABILITY OF MODERATE INTENSIFICATION FROM TAU 24 TO TAU 54. AFTER TAU 72, NUMERICAL MODEL GUIDANCE IS IN POOR AGREEMENT WITH A LARGE SPREAD IN TRACK FORECASTS. THE 171200Z ECMWF AND GEFS PROBABILISTIC GUIDANCE INDICATES A HIGH UNCERTAINTY IN THE TRACK OVER THE GULF OF TONKIN, REFLECTING THE WEAK, COMPETING STEERING ENVIRONMENT. IN GENERAL, BOTH THE DETERMINISTIC AND PROBABILISTIC GUIDANCE SUPPORT A STEADY WEAKENING TREND AFTER TAU 72. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN