WDPN32 PGTW 021500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (MALIKSI) WARNING NR 09// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 20W (MALIKSI), LOCATED APPROXIMATELY 200 NM SOUTH-SOUTHEAST OF IWO-TO, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY DEPICTS A LARGE SYSTEM WITH THE BULK OF CONVECTION OVER THE EASTERN SEMI-CIRCLE AND SOME CONVECTION WRAPPING AROUND A LOW-LEVEL CIRCULATION CENTER (LLCC). A 021000Z SSMIS 91GHZ MICROWAVE IMAGE DEPICTS THE SYSTEM HAS BECOME LESS ORGANIZED OVER THE PAST SIX HOURS WITH THE LLCC BECOMING SLIGHTLY ELONGATED AND THE CONVECTION NOT WRAPPING IN AS TIGHT AS IT WAS EARLIER. THE INITIAL POSITION BASED THE AFOREMENTIONED IMAGERY. THE INITIAL INTENSITY IS ASSESSED AT 40 KNOTS BASED ON AN AVERAGE OF CURRENT INTENSITY DVORAK ESTIMATES RANGING FROM 35 TO 45 KNOTS. UPPER LEVEL ANALYSIS INDICATES A MODERATE ENVIRONMENT WITH AN UPPER-LEVEL ANTICYCLONE NOW SLIGHTLY SEPARATED FROM THE SYSTEM BUT REMAINS IN AN AREA OF WEAK VERTICAL WIND SHEAR. TS 20W IS TRACKING NORTH-NORTHWESTWARD ALONG THE SOUTHWEST PERIPHERY OF A DEEP SUBTROPICAL RIDGE (STR) POSITIONED SOUTHEAST OF JAPAN. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 20W IS FORECAST TO INTENSIFY THROUGH TAU 36 DUE TO IMPROVING POLEWARD OUTFLOW ASSOCIATED WITH THE MIDLATITUDE TROUGH CURRENTLY OVER THE EAST CHINA SEA, AND WILL CONTINUE RE-CURVING POLEWARD AROUND THE STR. TS 20W IS THEN FORECASTED TO ACCELERATE NORTHWARD THEN NORTHEASTWARD AS IT ROUNDS THE STR AND WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) AROUND TAU 48 AND COMPLETE ETT BY TAU 72, AS IT BECOMES EMBEDDED IN THE BAROCLINIC ZONE. TS 20W IS EXPECTED TO PEAK NEAR TAU 36, PRIOR TO ENCOUNTERING INCREASING VERTICAL WIND SHEAR ASSOCIATED WITH THE DEEP MIDLATITUDE TROUGH AND COOLER SEA SURFACE TEMPERATURES. DYNAMIC MODEL GUIDANCE HAS COME INTO GOOD AGREEMENT BUT VARY SLIGHTLY IN THE TIMING AND POSITION OF THE RECURVE. THE OFFICIAL FORECAST IS SLIGHTLY FASTER THAN CONSENSUS DUE TO THE HISTORICAL BIAS. FORECAST CONFIDENCE CONTINUES TO IMPROVE, BUT REMAINS LOW BECAUSE OF THE TIMING OF TRACK SPEEDS.// NNNN