MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (PODUL) WARNING NR 04// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 13W (PODUL), LOCATED APPROXIMATELY 223 NM EAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 16 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD, PARTIALLY OBSCURED LOW LEVEL CIRCULATION WITH FLARING DEEP CONVECTION, PRIMARILY ALONG THE WESTERN PERIPHERY. THERE IS POOR CONFIDENCE IN THE INITIAL POSITION BASED ON THE MSI. THE CURRENT INTENSITY OF 30 KNOTS IS BASED ON MULTI-AGENCY DVORAK ESTIMATES BETWEEN T1.5-2.0 (25-30 KNOTS). THE ENVIRONMENT IS MARGINAL OVERALL WITH MODERATE-TO-STRONG (20-30 KT) VERTICAL WIND SHEAR (VWS) OFFSET BY FAVORABLE EQUATORWARD OUTFLOW AND WARM SEA SURFACE TEMPERATURE (29-30 CELSIUS). TD 13W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR). 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. THROUGH TAU 72, TD 13W WILL CONTINUE TO TRACK WESTWARD TO WEST- NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE STR TOWARDS SOUTHERN HAINAN. THE SYSTEM WILL MAKE LANDFALL OVER LUZON PRIOR TO TAU 12, QUICKLY TRANSIT THE ISLAND, AND EMERGE OVER THE SOUTH CHINA SEA (SCS) BY TAU 18. THE MARGINALLY FAVORABLE ENVIRONMENT WILL SUPPORT SOME INTENSIFICATION BEFORE LANDFALL, WEAKEN ONLY SLIGHTLY OVER LUZON DUE TO THE FAST TRANSIT SPEED, AND GRADUALLY INTENSIFY OVER THE SCS, REACHING 55 KTS BY TAU 72. THERE IS HIGH UNCERTAINTY IN THE INTENSITY FORECAST DUE TO SUSTAINED COMPETING ENVIRONMENTAL INFLUENCES. THERE IS FAIR CONFIDENCE IN THIS PORTION OF THE JTWC TRACK FORECAST BECAUSE AVAILABLE MODEL GUIDANCE IS IN FAIR GENERAL AGREEMENT. C. AFTER TAU 72, A SHORTWAVE TROUGH OVER EASTERN CHINA IS EXPECTED TO WEAKEN THE STR AND ALLOW THE SYSTEM TO TURN MORE POLEWARD TO THE WEST OF HAINAN ISLAND. THE INTENSITY IS FORECASTED TO GRADUALLY WEAKEN DURING THIS PERIOD DUE TO LAND INTERACTION WITH VIETNAM AND HAINAN BUT UNCERTAINTY IN THE INTENSITY FORECAST IS HIGH AS THE OUTFLOW MAY IMPROVE SIGNIFICANTLY DEPENDING ON TIMING OF TROUGH PASSAGE. AVAILABLE DYNAMIC MODEL GUIDANCE IS IN POOR AGREEMENT DUE TO DIFFERENCES IN THE TROUGH RESULTING IN SOME MODELS MAINTAINING A WESTWARD TRACK AND OTHERS DISPLAYING THE POLEWARD TURN. BASED ON THE COMPLEX STEERING ENVIRONMENT BEYOND TAU 72, THERE IS LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC FORECAST TRACK.// NNNN NNNN