WDPN32 PGTW 012100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 10W (TEN) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.3N 115.0E INITIAL INTENSITY: 25 KTS GEOGRAPHIC REFERENCE: 303 NM SOUTH OF HONG KONG MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A DISORGANIZED AND ASYMMETRIC SYSTEM IN THE SOUTH CHINA SEA (SCS). OVERNIGHT, TD 10W MAINTAINED A FULL EXPOSED LOW-LEVEL VORTEX, WITH INHIBITED CONVECTIVE DEVELOPMENT DUE TO PERSISTENT STRONG, NORTHERLY SHEAR. OVER THE PAST 2-3 HOURS, DEEP CONVECTION HAS REINITIATED AND EXPANDED IN AREAL COVERAGE AND THE LOW LEVEL CIRCULATION CENTER (LLCC) IS NOW POSITIONED BENEATH THE NORTHERN EDGE OF THE CONVECTIVE ENVELOPE. A LACK OF RECENT HIGH-RESOLUTION MICROWAVE IMAGERY PRECLUDES A DEFINITIVE ANALYSIS OF THE UNDERLYING VORTEX STRUCTURE, BUT THE PERSISTENCE OF THE MODERATE NORTHERLY SHEAR PROVIDES HIGH CONFIDENCE IN ASSESSING A MODERATE TO HIGH AMOUNT OF VERTICAL VORTEX TILT. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PREVIOUSLY EXPOSED LLCC IN THE ANIMATED PROXY VISIBLE IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, BASED ON EARLIER SCATTEROMETER DATA SHOWING A BROAD REGION OF 25 KNOT WINDS ALONG THE EASTERN FLANK OF THE CIRCULATION, SUPPORTED BY THE SUBJECTIVE AGENCY FIX ESTIMATES NOTED BELOW. ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE, WITH WARM SSTS, MODERATE EQUATORWARD OUTFLOW AND LOW TO MODERATE NORTHERLY SHEAR. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A LARGE DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED SOUTH OF JAPAN. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T1.5 - 25 KTS KNES: T1.5 - 25 KTS CIMSS D-PRINT: 27 KTS AT 011900Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-20 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE EQUATORWARD OTHER FACTORS: HIGHLY ASYMMETRIC AND VERTICALLY TILTED VORTEX. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH 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: TROPICAL DEPRESSION (TD) 10W WILL TRACK WEST-NORTHWESTWARD ALONG THE SOUTH-SOUTHWESTERN FLANK OF A DEEP STR OVER THE NEXT 12 HOURS, BEFORE TURNING NORTHWESTWARD AS THE WESTERN PERIPHERY OF THE RIDGE SLOWLY ERODES AND REORIENTS TO A MORE NORTHWEST-SOUTHEAST AXIS. TD 10W IS EXPECTED TO MAKE LANDFALL ALONG THE SOUTHEASTERN COAST OF HAINAN ISLAND AROUND TAU 36, QUICKLY CROSS THE ISLAND AND REEMERGE OVER THE GULF OF TONKIN PRIOR TO TAU 48. THE SYSTEM WILL CONTINUE TRACKING NORTHWESTWARD, MAKING A SECOND LANDFALL OVER SOUTHERN CHINA, JUST EAST OF THE SINO-VIETNAMESE BORDER REGION NEAR TAU 60, AND THEN BEGIN TO RECURVE AROUND THE WESTERN PERIPHERY OF THE STR WHILE CONTINUING FURTHER INLAND OVER SOUTHERN CHINA. IN TERMS OF INTENSITY, THE MODERATELY FAVORABLE CONDITIONS WILL SUPPORT A MODEST AMOUNT OF INTENSIFICATION, LIMITED BY THE ASYMMETRIC NATURE OF THE VORTEX AND THE LIMITED TIME OVER WATER. THE EXPLICIT FORECAST POINTS INDICATE A MAXIMUM OF 35 KNOTS, HOWEVER THE TRUE PEAK INTENSITY IS LIKELY TO OCCUR BETWEEN TAU 24 AND TAU 36, REACHING 40 KNOTS. AFTER LANDFALL ON HAINAN ISLAND, THE SYSTEM WILL WEAKEN TO 30-35 KNOTS, BUT QUICKLY REINTENSIFY ONCE REACHING THE WARM, HIGH-OHC WATERS OF THE GULF OF TONKIN. THE SHORT DURATION OVER OPEN WATER MEANS THE WINDOW FOR SYSTEM INTENSIFICATION WILL BE CONSTRAINED; HOWEVER, THE SYSTEM IS EXPECTED TO REACH A MAXIMUM OF 45-50 KNOTS PRIOR TO THE SECOND LANDFALL. ONCE ASHORE OVER SOUTHERN CHINA, THE SYSTEM WILL SLOWLY WEAKEN, FULLY DISSIPATING AS A TROPICAL CYCLONE NO LATER THAN TAU 96. MODEL DISCUSSION: TRACK GUIDANCE IS IN OVERALL GOOD AGREEMENT, WITH ALL MEMBERS OF THE CONSENSUS IN CONCURRENCE ON THE TRACK SCENARIO. CROSS-TRACK SPREAD AT LANDFALL IS 110NM, BETWEEN THE GEFS MEAN ON THE EASTERN SIDE AND THE JGSM ON THE WESTERN SIDE. THE GUIDANCE PACKAGE RETAINS THE SAME ORIENTATION AND CROSS-TRACK WIDTH THROUGH TAU 48 BEFORE WIDENING SLIGHTLY AFTER THE SECOND LANDFALL AS THE SYSTEM GRADUALLY WEAKENS. THE JTWC FORECAST IS PLACED NEAR THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN GENERALLY GOOD AGREEMENT, WITH ALL MODELS INDICATING A STEADY INTENSIFICATION RATE, WITH A SLIGHT WEAKENING OVER HAINAN, THROUGH THE SECOND LANDFALL. PEAK INTENSITY RANGES FROM A LOW-END ESTIMATE OF 35 KNOTS FROM THE SHIPS-NAVGEM TO 50 KNOTS IN FROM THE CTCX AND EXPERIMENTAL GDM FGNI. THE JTWC FORECAST IS PLACED CONSISTENT WITH THE HAFS-A GUIDANCE, WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN