MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (MEGI) WARNING NR 04// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A BROAD SYSTEM WITH IMPROVED FORMATIVE BANDING AND COOLING CLOUD TOPS ASSOCIATED WITH DEEP FLARING CENTRAL CONVECTION OVER THE LAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH POOR CONFIDENCE AND IS BASED ON A 231550Z AMSR2 IMAGE AND A 231218Z AMSU 89 GHZ IMAGE, BOTH SHOWING THE APPROXIMATE LOW LEVEL CIRCULATION CENTER WITH THE POSSIBILITY OF MULTIPLE VORTICES EXISTING AT THE SURFACE. THE INITIAL INTENSITY IS ASSESSED AT 35 KNOTS AND IS BASED ON THE LOWER END OF AGENCY DVORAK ESTIMATES RANGING FROM T2.5 TO T3.0 (35 TO 45 KNOTS). HIGHER DVORAK ESTIMATES ARE ATTRIBUTED TO IMPROVED CONVECTIVE ACTIVITY RELATED TO DIURNAL CHANGES, HOWEVER THE CIRCULATION REMAINS BROAD AND THE CONVECTIVE SIGNATURE OBSERVED IN THE AFOREMENTIONED MICROWAVE IMAGES DOES NOT WARRANT AN INTENSITY INCREASE AT THIS TIME. UPPER-LEVEL ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH A WELL-ESTABLISHED EQUATORWARD OUTFLOW CHANNEL AND A POLEWARD CHANNEL STARTING TO IMPROVE. VERTICAL WIND SHEAR IS LOW (5 TO 10 KNOTS) AND SSTS ARE FAVORABLE, NEAR 30 CELSIUS. CURRENTLY TS MEGI IS TRACKING NORTHWESTWARD ALONG THE PERIPHERY OF A MID TO LOW LEVEL SUBTROPICAL RIDGE POSITIONED TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. TS MEGI WILL CONTINUE TO TRACK NORTHWESTWARD THROUGHOUT THE FORECAST PERIOD AS THE STEERING RIDGE BUILDS AND EXTENDS WESTWARD. STEADY INTENSIFICATION IS EXPECTED THROUGH TAU 72 AS TS MEGI CONTINUES TO CONSOLIDATE WITHIN A VERY FAVORABLE ENVIRONMENT REACHING A PEAK INTENSITY OF 80 KNOTS. C. IN THE EXTENDED PERIOD, BEYOND TAU 72 TS MEGI IS EXPECTED TO CONTINUE ITS NORTHWESTERN TRACK MAKING LANDFALL OVER THE SOUTHERN PORTION OF TAIWAN WEAKENING RAPIDLY INTO A TROPICAL STORM. THIS TRACK WILL CONTINUE INTO CHINA BEFORE DISSIPATING NEAR TAU 120. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGHOUT THE FORECAST PERIOD WITH THE EXCEPTION OF GFDN DEPARTING FROM THE GROUP CLUSTER SHOWING A TRACK SIGNIFICANTLY SOUTH. THE FORECAST TRACK IS PLACED WITH GOOD CONFIDENCE LOCATED CLOSE TO THE MULTI-MODEL CONSENSUS.// NNNN NNNN