MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (CHAN-HOM) WARNING NR 18// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 09W (CHAN-HOM), LOCATED APPROXIMATELY 34 NM EAST-SOUTHEAST OF ROTA, HAS TRACKED NORTHWESTWARD AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED EIR SATELLITE IMAGERY DEPICTS SLIGHTLY DEEPENED CENTRAL CONVECTION OBSCURING THE LLCC. THE CURRENT POSITION IS BASED ON THE EIR LOOP, PGTW SATELLITE FIX AS WELL AS PGUA RADAR WITH GOOD CONFIDENCE. THE CURRENT INTENSITY REMAINS AT 40 KNOTS BASED ON AN OVERALL ASSESSMENT OF DVORAK INTENSITY ESTIMATES FROM ALL REPORTING AGENCIES. UPPER-LEVEL ANALYSIS INDICATES TS 09W IS NOW LOCATED IN AN AREA OF LOW TO MODERATE (05 TO 15 KNOT) VWS AND GOOD POLEWARD OUTFLOW THAT IS ENHANCED BY THE TUTT CELL TO THE NORTHEAST. TS 09W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF THE DEEP-LAYERED STR. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 09W WILL MAINTAIN A WEST-NORTHWESTWARD TO NORTHWESTWARD TRAJECTORY UNDER THE STEERING INFLUENCE OF THE STR ENTRENCHED TO THE NORTH. SLOW INTENSIFICATION IS EXPECTED AS CHAN-HOM TRACKS ACROSS THE MARIANA ISLANDS. AFTERWARD, UPPER-LEVEL CONDITIONS ARE FORECAST TO IMPROVE, ALLOWING TS 09W TO FURTHER INTENSIFY LEADING TO A PEAK INTENSITY OF 110 KNOTS. C. IN THE EXTENDED TAUS, TS 09W WILL CONTINUE TO TRACK NORTHWESTWARD UNDER THE INFLUENCE OF THE DOMINANT STEERING STR. VWS AND UPPER LEVEL DIVERGENCE WILL REMAIN FAVORABLE THROUGH THE END OF THE FORECAST PERIOD; HOWEVER, COOLER SST AND LOWER OHC VALUES WILL BEGIN TO WEAKEN THE SYSTEM. DYNAMIC MODEL GUIDANCE INDICATES SOME DIVERGENCE BEYOND TAU 96, BUT OVERALL REMAINS IN TIGHT AGREEMENT, LENDING TO HIGH CONFIDENCE IN THE JTWC TRACK FORECAST.// NNNN NNNN