MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (CHAN-HOM) WARNING NR 06// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 09W (CHAN-HOM), LOCATED APPROXIMATELY 582 NM EAST-SOUTHEAST OF ANDERSEN AFB, GUAM HAS TRACKED WESTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A DEEP CENTRAL DENSE OVERCAST FEATURE OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). A 011606Z SSMI 85GHZ MICROWAVE PARTIAL PASS IMAGE SHOWS A WELL DEFINED LLCC WITH TIGHT CURVED BANDING JUST EAST OF THE DEEPEST CONVECTION. THE INITIAL POSITION IS BASED ON THE AFOREMENTIONED MICROWAVE IMAGE AND SUPPORTED BY THE PGTW FIX WITH GOOD CONFIDENCE. THE INITIAL INTENSITY IS HELD AT 45 KNOTS BASED ON CONCURRING DVORAK INTENSITY ESTIMATES FROM ALL AGENCIES. UPPER LEVEL ANALYSIS INDICATES THAT THE SYSTEM IS LOCATED IN A MARGINALLY FAVORABLE ENVIRONMENT WITH LOW TO MODERATE (10 TO 20 KNOT) VERTICAL WIND SHEAR (VWS) AND EXCELLENT DIFFLUENT OUTFLOW ALOFT. TS 09W IS CURRENTLY TRACKING ALONG THE SOUTHERN PERIPHERY OF A SUB-TROPICAL RIDGE (STR) TO THE NORTH. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 09W WILL MAINTAIN A WESTWARD TRAJECTORY THROUGH TAU 36 UNDER THE INFLUENCE OF THE STEERING STR. MARGINALLY FAVORABLE CONDITIONS WILL PERSIST, ALLOWING GRADUAL INTENSIFICATION. BEYOND TAU 36, THE STEERING ENVIRONMENT BECOMES MORE COMPLEX AS TS CHAN-HOM INTERACTS WITH TROPICAL DISTURBANCE (94W) MENTIONED IN THE ABPW10 PGTW 010600. THIS INTERACTION WILL CAUSE TS 09W TO SLOW AND MAINTAIN CURRENT INTENSITY WITH A POTENTIAL WEAKENING PHASE. CONCURRENTLY, THE STR WILL BEGIN TO RETREAT TO THE EAST AS A MID-LATITUDE TROUGH PASSES TO THE NORTH, FORCING TS CHAN-HOM TO TURN NORTHWESTWARD. THE SYSTEM WILL BEGIN TO INTENSIFY AGAIN DUE TO FAVORABLE SEA SURFACE TEMPERATURES AND LOW VWS. C. TS 09W IS EXPECTED TO CONTINUE TRACKING NORTHWESTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD TOWARDS A BREAK IN THE STR AND CONTINUE TO INTENSIFY DUE TO FAVORABLE CONDITIONS. AVAILABLE MODEL GUIDANCE IS IN EXCELLENT AGREEMENT THROUGH TAU 36; HOWEVER, AS THE TS 09W INTERACTS WITH 94W, THE TRACK GUIDANCE FANS OUT REACHING 150NM AS THE SYSTEM PASSES THE MARIANA ISLANDS. DUE TO THE UNCERTAINTY DURING THE INTERACTION PHASE, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST.// NNNN NNNN