WDPN31 PGTW 110300 MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W WARNING NR 04// RMKS/ 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 110000Z TO 160000Z OCT 2005. A. TROPICAL STORM (TS) 21W (KIROGI), LOCATED APPROXIMATELY 430 NM SOUTHEAST OF OKINAWA, HAS TRACKED SOUTHWARD AT 05 KNOTS OVER THE PAST SIX HOURS. B. TS 21W IS CURRENTLY TRACKING SOUTHWARD SLOWLY UNDER THE IN- FLUENCE OF THE STEERING RIDGE TO THE WEST. INFLUENCE FROM A MID- LATITUDE TROUGH CURRENTLY LOCATED OVER THE YELLOW SEA WILL PROVIDE A POLEWARD PULL THAT WILL RESULT IN A NEAR STATIONARY MOVEMENT FOR THE NEXT 12 TO 24 HOURS. AFTER THE TROUGH PROPAGATES DOWNSTREAM, A RIDGE TO THE SOUTH OF THE SYSTEM WILL TAKE OVER AS THE MAIN STEERING MECHANISM, CAUSING A NORTHEASTERLY TRACK POLEWARD OF THE RIDGE AXIS. THE DYNAMIC AIDS CONSISTING OF NOGAPS, NCEP GFS, JGSM, JTYM, EGRR, GFDN, COAMPS, MM5, TCLAPS AND WBAR ARE IN POOR AGREEMENT WITH THIS SCENARIO. EACH MODEL SHOWS VARYING INTERACTION WITH THE MIDLATITUDE TROUGH SHOWING DISAGREEMENT IN LONGITUDINAL POSITIONING AT TAU 72. THIS FORECAST IS BASED UPON A CONSENSUS OF ALL AVAILABLE DYNAMIC AIDS AND PERSISTENCE. C. TS 21W IS FORECAST TO INTENSIFY GRADUALLY OVER THE NEXT 72 HOURS IN A FAVORABLE ENVIRONMENT. VERTICAL WIND SHEAR IN THE AREA IS LOW AND THE STORM SHOULD BENEFIT FROM A GOOD OUTFLOW CHANNEL ASSOCIATED WITH THE PASSAGE OF THE MIDLATITUDE TROUGH DISCUSSED ABOVE. THE PROXIMITY OF AN UPPER LEVEL LOW TO THE WEST OF THE SYSTEM IS FORECAST TO FILL AND NOT CONTRIBUTE SIGNIFICANTLY TO THE INTENSIFICATION OF TS 21W. HOWEVER, IF AN OUTFLOW CHANNEL BEGINS TO FORM, A MORE INTENSE STORM WOULD MOST LIKELY RESULT. D. CURRENT WIND RADII ARE BASED ON A 102119Z QUIKSCAT PASS. FORE- CAST WIND RADII ARE BASED ON CLIMATOLOGY FOR A SMALL TO AVERAGE SIZE SYSTEM. E. IN THE EXTENDED PERIOD TS 21W SHOULD CONTINUE A NORTHEASTERLY TRACK AROUND THE NORTHWESTERN PORTION OF THE STEERING RIDGE ANCHORED TO THE SOUTH. THE STORM WILL CONTINUE A GRADUAL INTENSIFICATION IN A FAVORABLE OUTFLOW AND LOW SHEAR ENVIRONMENT. 3. FORECAST TEAM: CHARLIE// NNNN