WDPN31 PGTW 301500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (FOUR) WARNING NR 004// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 04W (FOUR), LOCATED APPROXIMATELY 98 NM NORTH OF SONSOROL, HAS TRACKED WEST-NORTHWESTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED IMAGERY (EIR) INDICATES A DEEP CONSOLIDATED CENTRAL BALL OF CONVECTION WRAPPING AROUND A LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED UPON THE EIR LOOP AND EXTRAPOLATION FROM A 301002Z SSMIS 91GHZ MICROWAVE PASS. THE INITIAL INTENSITY OF 35KTS IS SET WITH FAIR CONFIDENCE BASED ON AN OVERALL ASSESSMENT OF MULTIPLE AGENCY DVORAK ESTIMATES OF T2.0/30KTS (PGTW/KNES), T1.5/25KTS (RJTD), T2.6/37KTS (ADT), AND SATELLITE CONSENSUS (SATCON) 36KTS. TD 04W REMAINS IN A FAVORABLE ENVIRONMENT WITH FAIR WESTWARD AND EQUATORWARD OUTFLOW, LOW (5-10KTS) VERTICAL WIND SHEAR (VWS) ALOFT, AND VERY WARM (30-31C) SEA SURFACE TEMPERATURES (SST) IN THE PHILIPPINE SEA. THE CYCLONE IS TRACKING ALONG THE SOUTHWEST PERIPHERY OF THE SUBTROPICAL RIDGE (STR) TO THE EAST-NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 04W WILL TRACK MORE NORTHWESTWARD OVER THE NEXT 72 HOURS UNDER THE STEERING INFLUENCE OF THE STR. THE SYSTEM WILL GRADUALLY INTENSIFY UNDER THE AFOREMENTIONED FAVORABLE CONDITIONS AND BY TAU 72, WHICH WILL REACH 60KTS. THE FORECAST TRACK IS LAID SLIGHTLY TO THE RIGHT AND AHEAD OF MODEL CONSENSUS DURING THE FIRST 72 HOURS TO OFFSET NAVGEM, GFS, AND AFUM TRACKERS, WHICH ARE TO THE LEFT OF THE MODEL ENVELOPE. AFTER TAU 72, THE FORECAST TRACK IS SLIGHTLY LEFT OF FORECAST CONSENSUS, OFFSETTING THE MORE EXTREME RIGHT OUTLIERS OF JGSM AND ECMWF. C. AFTER TAU 72, TD 04W WILL CONTINUE ON ITS NORTHWESTWARD TRACK UNDER THE SAME STR; HOWEVER, BY TAU 96, THE SYSTEM WILL BEGIN TO ROUND THE RIDGE AXIS THEN ACCELERATE NORTHEASTWARD. THE FAVORABLE CONDITIONS WILL PERSIST AND INTENSIFY THE CYCLONE SLIGHTLY, TO A PEAK INTENSITY OF 65KTS BY TAU 96. AFTERWARD, AS IT BECOMES EXPOSED TO INCREASED POLEWARD OUTFLOW ASSOCIATED WITH THE PREVAILING WESTERLIES UNDER THE POLAR FRONT JET, TD 04W WILL RAPIDLY DECAY DUE TO INCREASING VWS TO 45KTS BY TAU 120. NUMERICAL MODELS ALONG TRACK / CROSS TRACK ERRORS CONTINUALLY INCREASE FROM 276NM AT TAU 36 AND INCREASE TO A SPREAD GREATER THAN 570NM BY TAU 96 AS THE SYSTEM REACHES THE POLAR FRONT JET AND ROUNDS THE STR AXIS, LENDING LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC TRACK FORECAST.// NNNN