WDPN31 PGTW 180300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (ONE) WARNING NR 004// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 01W (ONE), LOCATED APPROXIMATELY 419 NM EAST OF DAVAO, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD AT 03 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY REVEALS AN EXPOSED, WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC), WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE, AND FORMATIVE DEEP CONVECTIVE BANDING OVER THE NORTHERN AND WESTERN SEMICIRCLES. A 172154Z SSMIS 91GHZ MICROWAVE IMAGE INDICATES MULTIPLE CONVECTIVE BANDS WRAPPING INTO THE WESTERN QUADRANT OF THE EXPOSED LLCC. THE INITIAL INTENSITY IS ASSESSED AT 35 KNOTS BASED ON A PGTW DVORAK ESTIMATE OF T2.5 (35 KNOTS) AND AN 180000Z ADT ESTIMATE OF 2.4 (34 KNOTS). UPPER-LEVEL ANALYSIS INDICATES A MARGINALLY-FAVORABLE ENVIRONMENT WITH MODERATE (20 KNOTS) EASTERLY VERTICAL WIND SHEAR (VWS) OFFSET BY DIFFLUENT EASTERLY FLOW AND ROBUST POLEWARD OUTFLOW. SST VALUES REMAIN CONDUCIVE AT 29-30C. TS 01W IS TRACKING ALONG THE SOUTHWEST PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 01W IS LOCATED WITHIN A WEAK STEERING ENVIRONMENT SOUTH OF A BREAK IN THE SUBTROPICAL RIDGE (STR) ASSOCIATED WITH A MAJOR SHORTWAVE TROUGH CURRENTLY OVER AND SOUTH OF JAPAN. IN GENERAL, THE SYSTEM WILL TRACK SLOWLY WESTWARD TO WEST-NORTHWESTWARD THROUGH TAU 48 UNTIL THE MAJOR TROUGH SHIFTS EASTWARD AND ZONAL FLOW PREDOMINATES. THIS WILL ALLOW THE STR TO RE-BUILD NORTHEAST AND NORTH OF THE SYSTEM, WHICH WILL ALLOW THE SYSTEM TO ACCELERATE WEST- NORTHWESTWARD WITH LANDFALL OCCURRING NEAR TAU 72. WITH THE EXCEPTION OF THE UKMET DETERMINISTIC AND UKMET ENSEMBLE MEAN SOLUTIONS, NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT WITH A 165NM SPREAD IN SOLUTIONS AT TAU 72. TS 01W WILL INTENSIFY STEADILY TO A PEAK INTENSITY OF 55 KNOTS BY TAU 36 TO TAU 48 UNDER GENERALLY FAVORABLE CONDITIONS, ESPECIALLY STRONG POLEWARD OUTFLOW. HOWEVER, THERE IS SOME UNCERTAINTY IN THE PEAK INTENSITY DUE TO THE PERSISTENT MODERATE VWS. C. AFTER TAU 72, TS 01W WILL TRACK ACROSS THE PHILIPPINE ARCHIPELAGO, AND BY TAU 120, WILL REACH THE SOUTH CHINA SEA OFF THE ISLAND OF MINDORO. INTERACTION WITH THE ISLANDS AND INCREASED VWS WILL WEAKEN THE SYSTEM DOWN TO 30 KNOTS BY TAU 120. NUMERICAL MODEL GUIDANCE DIVERGES BUT IS IN FAIR AGREEMENT IN THE EXTENDED PERIOD WITH A LARGE SPREAD OF 350NM AT TAU 120 (MINUS UKMET AND UKMET ENSEMBLE MEAN). THESE SOLUTIONS ARE RECURVING THE SYSTEM NORTH- NORTHWESTWARD, WHICH IS UNLIKELY DUE TO THE STRONG LIKELIHOOD OF A RE-BUILDING STR AND ZONAL UPPER-LEVEL FLOW OVER THE EAST CHINA SEA. SINCE THE PREVIOUS RUN, NAVGEM HAS COME INTO BETTER AGREEMENT WITH THE BULK OF THE GUIDANCE. OVERALL, THERE IS FAIR CONFIDENCE IN THE JTWC FORECAST TRACK, WHICH IS POSITIONED NEAR THE MULTI-MODEL CONSENSUS.// NNNN