MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 10W (MATMO) WARNING NR 06// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 10W (MATMO), LOCATED APPROXIMATELY 244 NM NORTH-NORTHWEST OF KOROR, PALAU, HAS TRACKED WESTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) DEPICTS LOW CLOUD LINES FEEDING INTO A LOW LEVEL CIRCULATION CENTER (LLCC) THAT IS OBSCURED BY DEEP CENTRAL CONVECTION THAT IS BEING SHEARED TO THE SOUTHWEST. THE INITIAL POSITION IS BASED ON A MICROWAVE EYE IN A 181615Z TRMM PASS WITH HIGH CONFIDENCE. THE INITIAL INTENSITY IS BASED ON CONGRUENT DVORAK ESTIMATES FROM PGTW AND RJTD. UPPER LEVEL ANALYSIS REVEALS A SEMI-CONDUCIVE ENVIRONMENT WITH GOOD EQUATORWARD OUTFLOW AND MODERATE (10 TO 20 KNOT) VERTICAL WIND SHEAR (VWS) WHILE AN UPPER-LEVEL TROUGH JUST TO THE NORTH IS MOMENTARILY CAUSING SUBSIDENCE ALONG THE NORTHWESTERN FLANK. THE CYCLONE IS TRACKING WESTWARD ALONG THE SOUTHERN EXTENSION OF A BUILDING SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 10W WILL BEGIN TRACKING MORE NORTHWESTWARD AS THE STR BECOMES THE DOMINANT STEERING INFLUENCE IN THE NEXT 36-48 HOURS. AFTERWARDS, A SHORTWAVE TROUGH APPROACHING FROM THE NORTHWEST WILL WEAKEN THE STR AND CAUSE A SLIGHTLY MORE POLEWARD TRACK TOWARDS TAIWAN. THE VWS IS EXPECTED TO RELAX AND POLEWARD OUTFLOW TO INCREASE AS THE SYSTEM GAINS LATITUDE. THESE, PLUS WARM SEA SURFACE TEMPERATURES IN THE PHILIPPINE SEA WILL PROMOTE GRADUAL INTENSIFICATION, REACHING 80 KNOTS BY TAU 72. C. IN THE EXTENDED TAUS, THE STR WILL RE-BUILD AFTER THE TROUGH PASSAGE AND CAUSE TS MATMO TO REVERT TO A FLATTER NORTHWESTWARD TRAJECTORY. THE FAVORABLE ENVIRONMENTAL CONDITIONS WILL PERSIST AND PROMOTE FURTHER INTENSIFICATION, PEAKING AT 95 KNOTS BY TAU 96 AFTER THE CYCLONE ENTERS THE LUZON STRAIT. THERE IS AN ALTERNATE SCENARIO WHERE THE AFOREMENTIONED SHORTWAVE TROUGH WILL BE DEEPER AND CAUSE A GREATER IMPACT ON THE STR. SHOULD THIS OCCUR, TS 09W WILL TRACK A LOT MORE POLEWARD TOWARDS OKINAWA AFTER TAU 72. THIS SCENARIO IS REFLECTED BY A MINORITY OF THE MODELS INCLUDING JENS, JGSM AND COTC. THE MAJORITY REMAINS WITH A GENERALLY NORTHWESTWARD TRACK. THE JTWC FORECAST TRACK IS LAID JUST TO THE LEFT OF THE MULTI-MODEL CONSENSUS AND FAVORS THE NORTHWEST TRACK. IN VIEW OF THE BIFURCATION IN THE NUMERIC MODELS, THE JTWC TRACK FORECAST IS HELD GUARDEDLY AT HIGH CONFIDENCE.// NNNN NNNN