WDPN32 PGTW 021500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (ATSANI) WARNING NR 017// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 23W (ATSANI), LOCATED APPROXIMATELY 505 NM NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY (EIR) SHOWS THE CENTRAL CONVECTION HAS SLIGHTLY DEEPENED, ALTHOUGH STILL DISPLACED WESTWARD FROM THE PARTIALLY EXPOSED LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLC IN THE EIR LOOP. THE INITIAL INTENSITY OF 30KTS IS BASED ON THE DVORAK ESTIMATES OF T2.0/30KTS FROM PGTW, KNES, AND RJTD. THE ENVIRONMENT IS MARGINALLY FAVORABLE WITH MODERATE (20-25KT) VERTICAL WIND SHEAR (VWS) AND WEAK OUTFLOW ALOFT OFFSET SLIGHTLY BY WARM (29-30C) SEA SURFACE TEMPERATURES (SST) IN THE PHILIPPINE SEA. THE CYCLONE IS TRACKING ALONG THE WESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE EAST-NORTHEAST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 23W WILL CONTINUE TO TRACK MORE POLEWARD, ALBEIT SLOWLY, AS IT ROUNDS THE WESTERN EDGE OF THE STR, AND BY TAU 12, NEST INTO A COL AREA SOUTH OF A SHORTWAVE MIDLATITUDE TROUGH AND BETWEEN THE STEERING STR AND A SECONDARY STR TO THE NORTHWEST, WHERE IT WILL REMAIN IN A QUASI-STATIONARY (QS) STATE UP TO TAU 48. AFTERWARD, THE PRIMARY STR WILL BUILD AND SLOWLY DRIVE TD 23W WEST-SOUTHWESTWARD AND OUT OF THE COL. THE ENVIRONMENT IS FORECAST TO IMPROVE AS VWS WEAKENS AND POLEWARD OUTFLOW INCREASES, FUELING A STEADY INTENSIFICATION TO A PEAK OF 65KTS BY TAU 72. NUMERICAL MODELS DIVERGE SIGNIFICANTLY WITH VARYING SOLUTIONS IN THE DURATION OF QS STATE IN THE COL, LENDING LOW CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK. C. IN THE EXTENDED TAUS, THE PRIMARY STR WILL CONTINUE TO STEER TD 23W WEST-SOUTHWESTWARD IN THE PHILIPPINE SEA, THROUGH LUZON STRAIT, AND INTO THE SOUTH CHINA SEA (SCS) BY TAU 120. THE ENVIRONMENT WILL DETERIORATE DUE TO INCREASING RELATIVE VWS AS THE CYCLONE TRACKS PERPENDICULAR TO THE UPPER LEVEL WIND FLOW, AND COOLING SST IN THE SCS, WEAKENING THE SYSTEM TO 50KTS BY TAU 120. NUMERICAL MODELS SIGNIFICANTLY DIVERGE TO OVER 1000 NM BY TAU 120 WITH NAVGEM AND UEMN SUGGESTING A RECURVATURE INTO JAPAN, LENDING LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC FORECAST THAT IS LAID WITH THE MAIN CLUSTER OF THE MODEL ENVELOPE.// NNNN