WDPN31 PGTW 220300 MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 26W WARNING NR 13// RMKS/ 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 220000Z4 TO 250000Z7 OCT 01. A. TYPHOON (TY) 26W (PODUL), LOCATED APPROXIMATELY 690 NM EAST OF GUAM, HAS BEEN TRACKING NORTHWARD AT 7 KNOTS DURING THE PAST SIX HOURS. THE WARNING POSITION IS BASED ON 212330Z1 INFRARED AND VISIBLE SATELLITE IMAGERY. THE WARNING INTENSITY IS BASED ON SATELLITE CURRENT INTENSITY ESTIMATES OF 75 KNOTS. THE 200 MB ANALYSIS REVEALS THAT TY 26W IS UNDER AN AREA OF DIFFLUENT FLOW ALOFT AND REMAINS IN A WEAK VERTICAL WIND SHEAR ENVIRONMENT. B. A WEAKNESS IN THE SUBTROPICAL RIDGE IS ALLOWING TY 26W TO TRACK NORTHWARD UNDER THE STEERING INFLUENCE OF THE NEAR-EQUATORIAL RIDGE SOUTH AND EAST OF THE SYSTEM. THE SUBTROPICAL RIDGE SHOULD REBUILD NORTH OF TY 26W AND BECOME THE DOMINANT STEERING MECHANISM LATER IN THE PERIOD. AS A RESULT, THE SYSTEM IS FORECAST TO TRACK NORTHWARD FOR 36 TO 48 HOURS AND THEN MORE NORTHWESTWARD FOR THE REMAINDER OF THE PERIOD. THE AVAILABLE DYNAMIC AIDS OF NOGAPS, NCEP AVIATION, GEOPHYSICAL FLUID DYNAMICS-NAVY (GFDN), THE UKMET OFFICE GLOBAL (EGRR), AND THE JMA GLOBAL (JGSM) AND TYPHOON (JTYM) MODELS ARE IN FAIR AGREEMENT WITH TWO DISTINCT CLUSTERS. JGSM, NCEP AVIATION, AND JTYM INDICATE A WEAK MID-LEVEL RIDGE NORTH OF THE SYSTEM AND TRACK THE SYSTEM MORE NORTHWARD INTO THE WEAKNESS THROUGH 48 HOURS, THEN CURVES NORTHWESTWARD FOR THE REMAINDER OF THE PERIOD. THE SECOND CLUSTER CONSISTING OF EGRR AND NOGAPS BUILD THE RIDGE TO THE NORTH, RESULTING IN A MORE NORTH-NORTHWESTWARD TRACK. OUR FORECAST IS BASED ON AN ENSEMBLE OF THE AVAILABLE DYNAMIC MODELS. C. TY 26W IS EXPECTED TO INTENSIFY AT A NEARLY CLIMATOLOGICAL RATE AS IT TRACKS INTO A FAVORABLE UPPER LEVEL ENVIRONMENT. D. WIND RADII ARE BASED ON CLIMATOLOGY FOR AN AVERAGE SIZE TROPICAL CYCLONE. FORECAST TEAM: MAZANY/WARREN/JACOBS/CUTMAN/NUTONGLA//