MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (CHOI-WAN) WARNING NR 01// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 23W (CHOI-WAN), LOCATED APPROXIMATELY 13 NM SOUTH-SOUTHEAST OF WAKE ISLAND, HAS TRACKED WEST-NORTHWESTWARD AT 02 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A VERY EXPANSIVE MONSOON DEPRESSION WITH A BROAD LOW-LEVEL CIRCULATION WITH FORMATIVE CONVECTIVE BANDS SLOWLY CONSOLIDATING TOWARDS A CENTROID. THE CENTROID IS SURROUNDED BY AT LEAST TWO WEAK ORBITING VORTICES. THE INITIAL POSITION IS BASED ON THE EIR LOOP AND ON A 021021Z ASCAT PASS. THE INITIAL INTENSITY OF 30 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF THE ASCAT DATA, DVORAK ESTIMATE FROM RJTD, AND SURFACE OBSERVATIONS FROM WAKE ISLAND AND A NEARBY SHIP. UPPER LEVEL ANALYSIS INDICATES A FAVORABLE UPPER-LEVEL ENVIRONMENT WITH NEAR RADIAL OUTFLOW AND LOW VERTICAL WIND SHEAR (VWS). ADDITIONALLY, SEA SURFACE TEMPERATURES AT 29-30 DEGREES CELSIUS, ARE HIGHLY CONDUCIVE FOR DEVELOPMENT. THE CYCLONE IS QUASI- STATIONARY AS IT CONSOLIDATES BETWEEN TWO STEERING MECHANISMS - A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTHWEST AND ANOTHER STR TO THE NORTHEAST. 3. FORECAST REASONING. A. THIS IS THE INITIAL PROGNOSTIC REASONING BULLETIN AND SETS THE FORECAST PHILOSOPHY FOR THIS SYSTEM. B. TD 23W IS EXPECTED TO SLOWLY TRACK GENERALLY WEST- NORTHWESTWARD AS IT TRANSITIONS INTO THE STEERING INFLUENCE OF THE STR TO THE NORTHWEST. THE FAVORABLE ENVIRONMENTAL CONDITIONS WILL PERSIST AND PROMOTE FURTHER INTENSIFICATION, REACHING TYPHOON STRENGTH BY TAU 72. AS THE SYSTEM CONSOLIDATES, THE FEEDER BANDS ARE EXPECTED TO WRAP TIGHTER INTO THE CIRCULATION CENTER, SHRINKING THE WIND RADII. C. IN THE EXTENDED TAUS, TD CHOI-WAN WILL BEGIN TO ROUND THE STR AND TRACK MORE POLEWARD. AS IT GAINS LATITUDE, VWS WILL INCREASE AND SSTS WILL DECREASE. HOWEVER, INCREASED POLEWARD OUTFLOW WILL OFFSET THESE NEGATIVE EFFECTS, VENTILATING THE CYCLONE TO A PEAK OF 70 KNOTS. AVAILABLE MODEL GUIDANCE IS IN RELATIVELY GOOD AGREEMENT, ESPECIALLY FOR A FIRST WARNING. HOWEVER, GIVEN THE UNCERTAINTY IN THE CURRENT STORM MOTION AND THE INITIAL PORTION OF THE FORECAST TRACK, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN