WDPN32 PGTW 302100 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: 8.2N 135.3E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 76 NM NORTHEAST OF KOROR MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) AND PROXY VISIBLE SATELLITE IMAGERY DEPICTS A COMPACT, WELL-DEFINED AND VERY TIGHTLY WRAPPING LOW LEVEL CIRCULATION CENTER (LLCC), WITH FLARING, DISORGANIZED CONVECTION TO THE SOUTHWEST. THE LLCC HAS ALTERNATIVELY BEEN EXPOSED COVERED BY CONVECTIVE BLOWOFF OVER THE PAST DAY AS CONVECTION HAS CONTINUALLY CYCLED, ONLY TO BE SHEARED OFF TO THE SOUTHWEST IN THE FACE OF PERSISTENT NORTHEASTERLY FLOW ALOFT. HOWEVER, WHILE THE CONVECTIVE STRUCTURE HAS REMAINED DISORGANIZED, THE STRUCTURE OF THE LOW-LEVEL CIRCULATION HAS STEADILY IMPROVED, AND LOW-LEVEL WIND FIELD HAS CONTINUED TO STRENGTHEN. RECENT SCATTEROMETER DATA INDICATED A COMPACT WIND FIELD WITH WINDS UP TO 30-35 KNOTS IN THE WEST-NORTHWEST SECTOR OF THE CIRCULATION. ADDITIONALLY, AGENCY FIXES HAVE BEEN IN THE T1.5-T2.0 FOR MORE THAN 24 HOURS, AND KNES HAS BEEN AT T2.5 FOR THE LAST COUPLE OF FIXES. THE CONGRUENCE OF THE ABOVE DATA LENDS INCREASED CONFIDENCE THAT WHILE THE SYSTEM DOES NOT LOOK ALL THAT IMPRESSIVE, THE WINDS ARE ABOVE THE WARNING THRESHOLD. THE ENVIRONMENT IS MARGINAL AT BEST, WITH WARM SSTS AND GOOD EQUATORWARD OUTFLOW BEING OFFSET BY PERSISTENT, STRONG NORTHEASTERLY FLOW ALOFT. THE 301200Z SOUNDING FROM YAP SHOWED 40-50 KNOT NORTHEASTERLIES ABOVE THE 300MB LEVEL, WHILE THE KOROR SOUNDING SHOWED THE WINDS ARE A BIT DIVERGENT AND WEAKER THAN AT YAP. CIMSS ANALYSIS REVEALS HIGHLY DIVERGENT FLOW IN THE IMMEDIATE VICINITY OF TD 27W, WHICH EXPLAINS THE REPEATED CYCLING OF THE CONVECTIVE FLARE-UPS. THE SYSTEM IS TRACKING WEST-SOUTHWEST ALONG THE SOUTHERN SIDE OF A DEEP SUBTROPICAL RIDGE TO THE NORTH. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) ENTRENCHED TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T1.5 - 25 KTS KNES: T2.5 - 35 KTS FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 20-25 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG EQUATORWARD 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: TD 27W WILL CONTINUE TRACKING TO THE WEST THROUGH THE FIRST 24 HOURS, THEN GRADUALLY TURN TO A MORE NORTHWESTWARD HEADING AFTER TAU 36 AS THE STEERING RIDGE PULLS AWAY TO THE NORTHEAST AND THE LOWER LEVEL FLOW BECOMES ORIENTED TO A NORTHWEST TO SOUTHEAST DIRECTION. WHILE THE SYSTEM HAS BEEN ABLE TO BECOME BETTER SYMMETRIZED AND INTENSIFY OVER THE PAST DAY OR SO, IT CANNOT CONTINUE THIS TREND IN THE FACE OF THE STRONG AND PERSISTENT NORTHEASTERLY SHEAR. THE LATEST CIMSS ANALYSIS ALSO SHOWS AN AREA OF CONVERGENCE UPSTREAM, WHICH IS EXPECTED TO PUSH DOWN ON TOP OF THE SYSTEM OVER THE NEXT 24 HOURS. THIS, ALONG A PUSH OF MID-LEVEL DRY AIR, AS REVEALED IN THE YAP SOUNDING, WILL KILL ANY POSSIBILITY OF INTENSIFICATION. THUS, THE FORECAST CALLS FOR A SLOW, STEADY DECLINE IN INTENSITY THROUGH THE FORECAST PERIOD, WITH THE SYSTEM FULLY DISSIPATING NO LATER THAN TAU 48, AND POTENTIALLY AS EARLY AS TAU 36, TO THE EAST OF THE PHILIPPINES. MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH THE FORECAST PERIOD, WITH ALL AVAILABLE CONSENSUS MEMBERS CONFINED TO A TIGHT, 70NM ENVELOPE, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST. INTENSITY GUIDANCE IS SURPRISINGLY MIXED, WITH THE MESOSCALE HWRF AND COAMPS-TC ALONG WITH THE GFS, INDICATING SLOW, STEADY WEAKENING WHILE THE DECAY-SHIPS BEING VERY AGGRESSIVE WITH INTENSIFYING THE SYSTEM UP TO 50 KNOTS IN THE CASE OF THE GFS VERSION. FOR THE REASONS OUTLINED ABOVE, THE INTENSIFICATION SCENARIO IS DEEMED HIGHLY UNLIKELY, THUS THE JTWC FORECAST ALIGNS WITH THE MESOSCALE MODELS, WITH HIGH CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: HIGH// NNNN