WDPN32 PGTW 010900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (ATSANI) WARNING NR 012// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 23W (ATSANI), LOCATED APPROXIMATELY 689 NM EAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 16 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A WEAK SYSTEM THAT HAS MAINTAINED AN OVERALL POORLY-ORGANIZED CONVECTIVE STRUCTURE. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON LOW-CLOUD TRACING INTO AN OBSCURED LOW LEVEL CIRCULATION IN THE MSI LOOP. THE INITIAL INTENSITY OF 30 KTS IS BASED ON THE DVORAK ESTIMATE ESTIMATE OF T2.0/30KTS FROM PGTW. THE ENVIRONMENT IS OVERALL UNFAVORABLE WITH MODERATE (20-25KT) VERTICAL WIND SHEAR (VWS) AND WEAK OUTFLOW ALOFT OFFSET BY WARM (29-30C) SEA SURFACE TEMPERATURES (SST). THE CYCLONE IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 23W WILL CONTINUE ON ITS CURRENT TRACK IN THE PHILIPPINE SEA UNDER THE AFOREMENTIONED STR. AFTER TAU 24, A SHORTWAVE MIDLATITUDE TROUGH APPROACHING FROM THE NORTHWESTWILL ERODE AND SPLIT THE STR AND PULL THE CYCLONE POLEWARD INTO A QUASI-STATIONARY STATE IN THE COL ZONE BETWEEN THE TWO RIDGES. THE ENVIRONMENT IS FORECAST TO IMPROVE SLIGHTLY AS VWS WEAKENS AND POLEWARD OUTFLOW IMPROVES, FUELING A STEADY INTENSIFICATION TO 60KTS BY TAU 72. NUMERICAL MODELS ARE IN GOOD AGREEMENT UP TO TAU 24 WITH NAVGEM THE SOLE OUTLIER TO THE RIGHT. AFTERWARD, THE 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 SECONDARY STR BEHIND THE SHORTWAVE TROUGH WILL ASSUME STEERING AND SLOWLY DRIVE TD 23W WESTWARD. ENVIRONMENTAL CONDITIONS ARE FORECAST TO IMPROVE EVEN MORE WITH DECREASED VWS (10-15KTS) AND THE ADDITION OF AN EQUATORWARD OUTFLOW CHANNEL. THESE CONDITIONS, COUPLED WITH CONTINUED WARM SST, WILL ALLOW FOR FURTHER INTENSIFICATION TO 85KTS AS IT CROSSES THE LUZON STRAIT. NUMERICAL MODELS SIGNIFICANTLY DIVERGE TO 400 NM BY TAU 120 WITH VARYING TRACK SPEEDS, LENDING POOR CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC FORECAST TRACK.// NNNN