WDPN32 PGTW 170300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (USAGI) WARNING NR 02// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 17W (USAGI), LOCATED APPROXIMATELY 582 NM SOUTH-SOUTHEAST OF KADENA AB, HAS TRACKED WEST-SOUTHWESTWARD AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) THAT HAS BEEN STEADILY CONSOLIDATING INTO A SYMMETRIC CIRCULATION OVER THE PAST FEW HOURS. A RECENT BLOOM OF DEEP CONVECTION NEAR THE LLCC HAS RECENTLY DEVELOPED AND IS CURRENTLY LINKED TO THE BAND OF DEEP CONVECTION THAT HAS PERSISTED WITHIN THE SOUTHWESTERN QUADRANT. THE SECONDARY BAND OF DEEP CONVECTION IN THE SOUTH-EASTERN QUADRANT HAS BEEN STRUGGLING TO WRAP FULLY INTO THE LLCC ALONG THE EASTERN HALF OF THE SYSTEM. THE CURRENT INTENSITY HAS BEEN INCREASED TO 30 KNOTS BASED ON THE IMPROVING ORGANIZATION TO THE LLCC AND DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD RANGING FROM 25 TO 35 KNOTS. UPPER LEVEL ANALYSIS INDICATES A POINT-SOURCE ANTICYCLONE IS DEVELOPING OVER THE LLCC WITH A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL LOCATED TO THE EAST. THE TUTT CELL, IN ASSOCIATION WITH THE ANTICYCLONE, IS ENHANCING THE OUTFLOW IN THE EASTERN AND SOUTHERN QUADRANTS. TD 17W IS SLOWLY TRACKING WESTWARD IN A RELATIVELY WEAK STEERING ENVIRONMENT. THE REMNANTS OF TS 16W (MAN-YI) HAVE WEAKENED THE DEEP LAYERED SUBTROPICAL RIDGE (STR) THAT EXTENDS FROM CENTRAL CHINA THROUGH THE CENTRAL PACIFIC LEADING TO TD 17W BEING LOCATED WITHIN A COL REGION. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 17W IS EXPECTED TO SLOWLY TRACK WESTWARD AS THE REMNANTS OF TS 16W MOVE TO THE NORTHEAST. THE STR IS EXPECTED TO REBUILD TO THE NORTH OF TD 17W ALLOWING FOR THE SYSTEM TO INCREASE IN TRACK SPEED OVER THE NEXT 36 TO 48 HOURS. THE SEA SURFACE TEMPERATURES ALONG THE FORECAST TRACK ARE FAVORABLE (29 TO 30 CELSIUS) FOR DEVELOPMENT THROUGHOUT THE FORECAST PERIOD. THE UPPER LEVEL TUTT CELL WILL CONTINUE TO ENHANCE THE EASTWARD OUTFLOW THROUGH TAU 36 AS IT TRACKS TO THE WEST-NORTHWEST OVER THE NEXT FEW DAYS. THERE IS SOME CONCERN REGARDING THE INTERACTION BEYOND TAU 48 AS TD 17W AND THE TUTT CELL TRACK ON SEPARATE BEARINGS. MODERATELY FAVORABLE OUTFLOW WILL CONTINUE TO ENHANCE THE DEVELOPMENT OF THE SYSTEM THROUGH TAU 72. C. IN THE EXTENDED TAUS, TD 17W WILL CONTINUE TO TRACK ALONG THE SOUTHERN PERIPHERY OF THE STR, TOWARDS THE SOUTHERN TIP OF TAIWAN. THE OVERALL ENVIRONMENT IS EXPECTED TO REMAIN FAVORABLE THROUGH TAU 96, BUT SHORTLY BEFORE TAU 120, LAND INTERACTION WITH TAIWAN WILL CAUSE A BRIEF WEAKENING OF THE SYSTEM. NUMERIC MODEL GUIDANCE IS IN FAIR AGREEMENT WITH THE GENERAL WESTWARD TRACK THROUGH TAU 72, BUT INDICATES A LARGE VARIATION IN THE AMOUNT OF INTERACTION THE STR WILL PLAY AS TD 17W APPROACHES TAIWAN. THE CURRENT FORECAST TRACK IS BASED ON THE CONSENSUS OF AVAILABLE MODEL GUIDANCE. DUE TO THE VARIATIONS IN MODEL GUIDANCE, CONFIDENCE IN THE FORECAST TRACK REMAINS LOW.// NNNN