WDPN31 PGTW 220300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (THIRTEEN) WARNING NR 06// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 13W (THIRTEEN), LOCATED APPROXIMATELY 255 NM SOUTH-SOUTHEAST OF TAIPEI, TAIWAN, HAS TRACKED NORTHEASTWARD AT 15 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A COMPACT SYSTEM WITH DEEP CONVECTION OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH POOR CONFIDENCE BASED ON A 212243Z SSMIS 91 GHZ IMAGE SHOWING CONVECTION WRAPPING AROUND A POORLY DEFINED LLCC. THE INITIAL INTENSITY OF 30 KNOTS IS BASED ON DVORAK CURRENT INTENSITY ESTIMATES OF T2.0 (30 KNOTS) FROM PGTW, KNES, AND RJTD. ENVIRONMENTAL ANALYSIS INDICATES WEAK EQUATORWARD OUTFLOW, LOW VERTICAL WIND SHEAR (15 KNOTS), AND WARM SEA SURFACE TEMPERATURES (29-30 CELSIUS). TD 13W IS TRACKING NORTHEASTWARD DUE TO A SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. THE STR WILL BUILD TO THE WEST, CAUSING TD 13W TO TURN NORTHWESTWARD BY TAU 24. BEYOND TAU 24, TD 13W WILL CONTINUE TO TRACK NORTHWESTWARD UNTIL MAKING LANDFALL SOUTH OF SHANGHAI, CHINA BY TAU 48. ENVIRONMENTAL CONDITIONS WILL REMAIN UNFAVORABLE FOR INTENSIFICATION AND TD 13W WILL REMAIN BELOW TROPICAL STORM STRENGTH UNTIL LANDFALL WHEN IT WILL WEAKEN BELOW WARNING LEVELS BY TAU 72. DYNAMIC MODEL GUIDANCE GENERALLY AGREES ON THE FORECAST TRACK THROUGH TAU 24. BEYOND TAU 24, MANY MEMBERS LOSE THE CIRCULATION WHILE THE REMAINDER OF THE MEMBERS FOLLOW A TRACK SIMILAR TO THE OFFICIAL JTWC FORECAST TRACK. BASED ON THE MODEL SPLIT, IT IS POSSIBLE TD 13W WILL FALL BELOW WARNING THRESHOLD BEFORE MAKING LANDFALL. BASED ON THE HIGH UNCERTAINTY IN THE MODEL GUIDANCE, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN