MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 13W (THIRTEEN) WARNING NR 01// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 13W (THIRTEEN), LOCATED APPROXIMATELY 498 NM EAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 20 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION WITH FLARING DEEP CONVECTION OVER THE WESTERN SEMICIRCLE. A 261012Z SSMIS 91GHZ COLOR COMPOSITE MICROWAVE IMAGE INDICATES FRAGMENTED BANDING WRAPPING INTO A BROAD LLCC, THEREFORE, THERE IS FAIR CONFIDENCE IN THE CURRENT POSITION. THE CURRENT INTENSITY IS ASSESSED AT 25 KNOTS BASED ON A 261218Z PARTIAL ASCAT IMAGE SHOWING 20-25 KNOT WINDS OVER THE EASTERN SEMICIRCLE AS WELL AS A 26/1200Z SHIP OBSERVATION, 130NM SOUTH, SHOWING WEST-NORTHWESTERLY SURFACE WINDS AT 22 KNOTS WITH SLP NEAR 1004MB. ENVIRONMENTAL ANALYSIS REVEALS A MARGINALLY-FAVORABLE ENVIRONMENT WITH MODERATE TO STRONG VERTICAL WIND SHEAR OFFSET BY STRONG DIFFLUENCE ALOFT AND WARM SST (28-30C). TD 13W IS TRACKING WESTWARD ALONG THE SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) ENTRENCHED TO THE NORTH. 3. FORECAST REASONING. A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE AND SETS THE FORECAST PHILOSOPHY. B. IN THE NEAR TERM, TD 13W WILL TRACK WEST-NORTHWESTWARD MAKING LANDFALL OVER EASTERN LUZON NEAR TAU 24. DUE TO THE MARGINALLY- FAVORABLE ENVIRONMENT, THE SYSTEM IS EXPECTED TO INCREASE TO MINIMAL TROPICAL STORM STRENGTH (35 KNOTS) AT TAU 24. TD 13W WILL WEAKEN AS IT CROSSES LUZON BUT SHOULD RE-INTENSIFY AFTER TAU 48 AS CONDITIONS GRADUALLY IMPROVE. THE SYSTEM IS EXPECTED TO CONTINUE TRACKING WESTWARD TO WEST-NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR POSITIONED TO THE NORTH THROUGH TAU 72. C. AFTER TAU 72, A DEEP SHORTWAVE TROUGH IS FORECAST TO DIG OVER EASTERN CHINA WHICH WILL WEAKEN THE STR AND ALLOW THE SYSTEM TO TURN MORE POLEWARD TOWARD HAINAN ISLAND. THE SYSTEM SHOULD INTENSIFY TO A PEAK INTENSITY OF 50 KNOTS BY TAU 96. AFTER TAU 96, TD 13W SHOULD STEER WESTWARD AS IT TRANSITIONS TO THE WESTERN STR. THE DYNAMIC MODEL GUIDANCE IS IN FAIR AGREEMENT WITH TWO OUTLIERS (NAVGEM AND JGSM), THEREFORE, THERE IS LOW CONFIDENCE IN THE FORECAST TRACK.// NNNN NNNN