WDPN31 PGTW 170900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (ONE) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 01W (ONE), LOCATED APPROXIMATELY 88 NM WEST- SOUTHWEST OF KOROR, REPUBLIC OF PALAU, HAS TRACKED WESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS FORMATIVE RAIN BANDS WITH FRAGMENTED DEEP CONVECTION LOOSELY WRAPPING INTO AN OBSCURED LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON LOW CLOUD TRACING IN THE MSI LOOP INTO THE OBSCURED LLC AND LINED UP WITH A FORMATIVE LLC FEATURE IN THE 170447Z GCOM MICROWAVE IMAGE. THE INITIAL INTENSITY OF 25KTS IS BASED ON THE DVORAK ESTIMATES OF T1.5/25KTS FROM PGTW AND RJTD AND EXTRAPOLATED FROM THE WIND AND PRESSURE OBSERVATION FROM KOROR, THAT SAW A 5MB DROP IN 24 HOURS TO 1003MB. ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH LOW (10- 15KT) EASTERLY RELATIVE VERTICAL WIND SHEAR, ROBUST WESTWARD AND POLEWARD UPPER LEVEL OUTFLOW THAT IS PROVIDING AMPLE VENTILATION TO THE CONVECTION, AND WARM (29-30C) ALONG-TRACK SST IN THE PHILIPPINE SEA. THE CYCLONE IS TRACKING ALONG THE SOUTHWEST PERIPHERY OF A DEEP- LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 3. FORECAST REASONING. A. THIS IS THE INITIAL PROGNOSTIC REASONING MESSAGE AND SETS THE FORECAST PHILOSOPHY FOR THIS SYSTEM. B. TD 01W IS WILL TRACK MORE NORTHWESTWARD FOR THE DURATION OF THE FORECAST UNDER THE STEERING INFLUENCE OF THE STR TO THE NORTHEAST. THE FAVORABLE ENVIRONMENT WILL PROMOTE STEADY INTENSIFICATION TO A PEAK OF 55KTS BY TAU 72 AS THE SYSTEM APPROACHES CENTRAL PHILIPPINES. C. BEYOND TAU 72, TD 01W WILL MAKE LANDFALL OVER LEYTE BY TAU 96 AND TRACK ACROSS THE PHILIPPINE ARCHIPELAGO, AND BY TAU 120, WILL BE OVER THE ISLAND OF MINDORO, APPROXIMATELY 90NM SOUTH OF MANILA. INTERACTION WITH THE ISLANDS WILL ERODE THE SYSTEM DOWN TO 30KTS BY TAU 120. NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT AND EVENLY SPREAD OUT; HOWEVER, DUE TO THE UNCERTAINTY IN THE INITIAL STORM MOTION OF THIS DEVELOPING CYCLONE, THERE IS LOW CONFIDENCE IN THE FIRST JTWC TRACK FORECAST ON THIS SYSTEM.// NNNN