WDPN31 PGTW 010900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 27W (TWENTYSEVEN) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.7N 130.8E INITIAL INTENSITY: 25 KTS GEOGRAPHIC REFERENCE: 569 NM EAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS SIGNIFICANT WAVE HEIGHT: 10 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL DEPRESSION 27W WITH FRAGMENTED BANDING AND FLARING CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 010457Z AMSR2 89 GHZ MICROWAVE IMAGE SHOWED THE IMPROVED CONVECTIVE BANDING WITHIN THE NORTHERN AND SOUTHWESTERN PERIPHERIES OF THE SYSTEM. ENVIRONMENTAL ANALYSIS INDICATES THAT 27W IS IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD AND EQUATORWARD OUTFLOW, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED AMSR2 MICROWAVE IMAGE AND ANIMATED MSI. THE INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES RANGING FROM T1.5-2.0 AND A CIMSS DPRINT ESTIMATE OF 23 KTS AT 010600Z. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE POSITIONED TO THE NORTH AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T1.5 - 25 KTS KNES: T1.5 - 25 KTS CIMSS D-PRINT: 23 KTS AT 010600Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD AND EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: 27W IS FORECAST TO TRACK WEST-NORTHWESTWARD, UNDER THE INFLUENCE OF THE BUILDING SUBTROPICAL RIDGE TO THE NORTH THROUGHOUT THE ENTIRE FORECAST PERIOD. AN INITIAL LANDFALL IS CURRENTLY FORECAST TO OCCUR BETWEEN TAU 36 AND 48, ALONG THE SOUTHEASTERN PORTION OF THE CAGAYAN PROVINCE. A SECOND LANDFALL IS THEN FORECAST TO OCCUR AROUND TAU 96, NEAR THE LEIZHOU PENINSULA. REGARDING INTENSITY, 27W IS FORECAST TO MARGINALLY INTENSIFY OVER THE NEXT 12 HOURS AS THE WIND FIELD CONTINUES TO CONSOLIDATE. AFTER TAU 12, A RAPID, OR NEAR-RAPID RATE OF INTENSIFICATION IS EXPECTED AS SHEAR REMAINS VERY LOW AND THE POLEWARD OUTFLOW CHANNEL IMPROVES. A BORDERLINE TYPHOON STRENGTH SYSTEM IS FORECAST TO MAKE LANDFALL WITHIN NORTHEASTERN LUZON. A BRIEF PERIOD OF STAGNATION IN THE INTENSITY TREND IS EXPECTED AS THE SYSTEM TRACKS ALONG NORTHERN LUZON. ANOTHER PERIOD OF INTENSIFICATION IS FORECAST AS 27W TRAVERSES THROUGH THE SOUTH CHINA SEA IN RESPONSE TO THE FAVORABLE ENVIRONMENT IN THE AREA. A PEAK INTENSITY WILL LIKELY OCCUR NEAR TAU 84, WHICH IS NOT CAPTURED BY THE FORECAST DUE TO TEMPORAL RESTRICTIONS. AFTER MAKING LANDFALL IN SOUTHERN CHINA, TERRAIN INTERACTION WILL RAPIDLY DETERIORATE THE VORTEX. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH TAU 96. AT TAU 48 THERE IS A 65 NM CROSS-TRACK SPREAD AND AT TAU 96 THERE IS A 130 NM CROSS-TRACK SPREAD. AFTER TAU 96, MODELS BEGIN TO DIVERGE DUE TO THE RAPIDLY WEAKENING VORTEX. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER. INTENSITY HAS MORE UNCERTAINTY WITH MANY RAPID INTENSIFICATION AIDS TRIGGERING THROUGH THE FIRST 36 HOURS OF THE FORECAST PERIOD. PEAK INTENSITIES AT TAU 84 RANGE FROM 60 KTS (GFS) TO 85 KTS (COAMPS-TC). AI MODELS SUGGEST AN EVEN HIGHER PEAK OF AROUND 100 KTS. THE JTWC INTENSITY FORECAST IS PLACED JUST UNDER THE RAPID INTENSIFICATION AIDS THROUGH TAU 36 AND THEN ABOUT 5-10 KTS ABOVE THE CONSENSUS THROUGH TAU 96 WITH OVERALL LOW CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN