WDPN31 PGTW 292100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (FOUR) WARNING NR 001// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 04W (FOUR), LOCATED APPROXIMATELY 56 NM SOUTH OF PALAU, HAS TRACKED WESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A RAPIDLY CONSOLIDATING SYSTEM WITH FRAGMENTED, FORMATIVE BANDS WRAPPING INTO A DEFINED LOW LEVEL CIRCULATION (LLC). THE EIR LOOP ALSO SHOWS OVERSHOOTING CLOUD TOPS OVER THE CENTRAL CONVECTION. A 291709Z ATMS 88.2GHZ MICROWAVE SATELLITE PASS HIGHLIGHTS THE DEEP CENTRAL CONVECTION THAT IS OFFSET SOUTHWESTWARD OF THE LLC. THE INITIAL POSITION IS BASED WITH FAIR CONFIDENCE ON A NOTCH FEATURE ALONG THE NORTHEAST QUADRANT OF THE AFOREMENTIONED MICROWAVE IMAGERY AND PLACED ADJACENT TO THE 291740Z PGTW SATELLITE FIX. THE INITIAL INTENSITY IS SET WITH FAIR CONFIDENCE BASED ON THE PGTW AND KNES DVORAK ESTIMATES OF T1.5(25KTS) AND EXTRAPOLATED FROM THE WIND AND SEA LEVEL PRESSURE OBSERVATIONS FROM PALAU. TD 04W IS IN A FAVORABLE ENVIRONMENT WITH GOOD RADIAL 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. THIS IS THE INITIAL PROGNOSTIC REASONING BULLETIN ON THIS SYSTEM AND SETS THE FORECAST PHILOSOPHY. B. TD 04W IS FORECAST TO CONTINUE NORTHWESTWARD OFFSHORE AND PARALLEL TO THE EAST COAST OF THE PHILIPPINES OVER THE NEXT 72 HOURS UNDER THE STEERING INFLUENCE OF THE STR. THE SYSTEM IS FORECAST TO RAPIDLY INTENSIFY UNDER THE AFOREMENTIONED FAVORABLE CONDITIONS, REACHING 45KTS BY TAU 24. AFTERWARD, INTENSIFICATION WILL BE MORE GRADUAL AS VWS BECOMES MORE MODERATE (15-20KTS), AND BY TAU 72 WILL REACH 60KTS. THE FORECAST TRACK IS LAID SLIGHTLY TO THE LEFT AND AHEAD OF MODEL CONSENSUS DURING THE FIRST 36 HOURS DUE TO THE UKMET TRACKER BEING SLOW AND TO THE RIGHT OF THE MODEL ENVELOPE, SHOWING A MORE DIRECT NORTHWARD TRANSIT. AFTER TAU 36, THE FORECAST TRACK IS MORE ALIGNED, ALBEIT SLIGHTLY AHEAD OF CONSENSUS. C. AFTER TAU 72, TD 04W WILL BEGIN TO ROUND THE RIDGE AXIS THEN ACCELERATE NORTHEASTWARD. AT THIS STAGE, IT WILL ALSO BE OVER THE WARMEST WATERS (31-32C) OF ITS FORECAST TRACK AND VWS WILL WEAKEN TO 05-10KTS, FUELING THE INTENSITY TO TYPHOON STRENGTH OF 65KTS. BY TAU 120, THE SYSTEM WILL REACH 70KTS AS IT BECOMES EXPOSED TO INCREASED POLEWARD OUTFLOW ASSOCIATED WITH THE PREVAILING WESTERLIES UNDER THE POLAR FRONT JET. NUMERICAL MODELS REMAIN IN GOOD AGREEMENT, LENDING ALSO FAIR CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC FORECAST TRACK.// NNNN