MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (TWENTYTHREE) WARNING NR 05// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 23W (TWENTYTHREE), LOCATED APPROXIMATELY 128 NM NORTH-NORTHWEST OF DA NANG, VIETNAM, HAS TRACKED WEST- NORTHWESTWARD AT 19 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS RAGGED BANDS OF DEEP CONVECTION WRAPPING AROUND AN ILL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC). DETERMINING THE EXACT CENTER HAS BEEN CHALLENGING, HIGHLIGHTED BY THE LARGE SPREAD IN AVAILABLE FIX ESTIMATES. RECENT PASSES BY ASCAT AND OSCAT (STILL UNDER TESTING AND EVALUATION) PROVIDED SOME DETAIL OF THE OVERALL STRUCTURE, WITH ENHANCED (25-30 KNOT) EASTERLIES TO THE NORTH ALONG THE CHINESE COAST, AND WEAK (5- 10 KNOT) WESTERLY FLOW TO THE SOUTH OF THE LLCC. THE TRACK WAS SHIFTED SLIGHTLY SOUTH BASED ON THIS DATA. THE INITIAL POSITION IS BASED ON THE EIR LOOP, AND SUPPORTED BY OBSERVATIONS FROM STATION 48846 (12 KNOTS FROM 50 DEGREES AND 1001.5 MB MSLP) AND STATION 48848 FURTHER SOUTH (1-2 KNOTS FROM 230 DEGREES AND 1000.2 MB MSLP). THE INITIAL INTENSITY OF 30 KNOTS IS HEDGED ABOVE PGTW AND RJTD DVORAK ESTIMATES OF T1.5 (25 KNOTS) BASED ON THE AFOREMENTIONED SCATTEROMETRY DATA, HOWEVER, THE PEAK WINDS ARE CONSTRAINED TO THE NORTHERN GULF OF TONKIN. UPPER LEVEL ANALYSIS REVEALS WELL ESTABLISHED OUTFLOW, HOWEVER, FURTHER DEVELOPMENT HAS BEEN CONSTRAINED DUE TO 20+ KNOT VERTICAL WIND SHEAR VALUES. SEA SURFACE TEMPERATURES REMAIN FAVORABLE (28-29 CELSIUS). TD 23W IS TRACKING WEST-NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE MID-LAYER SUBTROPICAL RIDGE (STR) TO THE NORTH. 3. FORECAST REASONING. A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 23W WILL CONTINUE TRACKING WEST-NORTHWESTWARD AND MAKE LANDFALL OVER CENTRAL VIETNAM IN THE NEXT FEW HOURS. THE SYSTEM WILL WEAKEN RAPIDLY AS IT MOVES AWAY FROM THE ENHANCED MARITIME WINDS. MODEL GUIDANCE IS IN GOOD AGREEMENT FOR BOTH TRACK AND INTENSITY. OVERALL CONFIDENCE FOR THE JTWC FORECAST IS HIGH.// NNNN NNNN