WDPN31 PGTW 222100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION TD (TWENTYEIGHT) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 10.4N 113.3E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 390 NM EAST OF HO CHI MINH CITY, VIETNAM MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 13 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP CONVECTION FLARING OVER THE NORTHWESTERN PERIPHERY OF A MOSTLY EXPOSED LOW-LEVEL CIRCULATION EVIDENT IN A 221928Z GMI PASS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A RECENT PGTW SATELLITE POSITION FIX AND 37 GHZ MICROWAVE IMAGERY FROM THE 221928Z GMI PASS. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON A CONSENSUS OF SUBJECTIVE DVORAK AND AUTOMATED INTENSITY ESTIMATES AS WELL AS SUPPORTIVE 221547Z OSCAT AND 22731Z AMSR2 WIND SPEED DATA. THE SYSTEM POSITION ESTIMATE HAS BEEN RELOCATED APPROXIMATELY 70 NM TO THE SOUTH-SOUTHEAST OF THE PREVIOUSLY FORECASTED 221800Z POSITION BASED ON CURRENT HIGH CONFIDENCE FIXES ON THE EXPOSED LOW-LEVEL CIRCULATION CENTER. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: SUBTROPICAL RIDGING (STR) TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.5 - 25 KTS KNES: T1.5 - 25 KTS CIMSS ADT: 27 KTS AT 221730Z CIMSS AIDT: 27 KTS AT 221730Z CIMSS D-MINT: 30 KTS AT 221754Z CIMSS D-PRINT: 39 KTS AT 221900Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-20 KTS SST: 27-28 CELSIUS OUTFLOW: MODERATE POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THE FORECAST TRACK HAS SHIFTED TO THE SOUTH FROM THE PREVIOUS WARNING CONSISTENT WITH RELOCATION OF THE ANALYSIS POSITION. THE OVERALL FORECAST PHILOSOPHY IS UNCHANGED FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE. FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 28W WILL CONTINUE TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF THE STR FOR THE NEXT 12 HOURS. THEREAFTER, THE STEERING RIDGE IS EXPECTED TO BUILD INTO A MORE CONTINUOUS WEST TO EAST ORIENTATION AS A SHORTWAVE TROUGH CURRENTLY ANALYZED OVER THE NORTHWESTERN PORTION OF THE SOUTH CHINA SEA TRANSLATES EASTWARD. THE REORIENTED RIDGE WILL STEER THE SYSTEM WESTWARD TO WEST-SOUTHWESTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD. ADDITIONAL INTENSIFICATION IS EXPECTED IN THE NEAR-TERM AS THE SYSTEM ENCOUNTERS STRONG LOW-LEVEL NORTHEASTERLY FLOW ASSOCIATED WITH A COLD SURGE OVER THE WESTERN PORTION OF THE SOUTH CHINA SEA, RESULTING IN INCREASED CONVECTION OVER THE WESTERN PERIPHERY AND WRAPPING OF STRONGER SURGE-ASSOCIATED ENVIRONMENTAL WINDS AROUND THE STORM CIRCULATION. STEADY DISSIPATION IS VERY LIKELY AFTER TAU 24 AS VERTICAL WIND SHEAR INCREASES, DRY AIR WRAPS IN TOWARD THE LOW-LEVEL CIRCULATION CENTER, AND THE SYSTEM MOVES OVER GRADUALLY COOLER WATER. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT REGARDING THE OVERALL FORECAST SCENARIO, BUT THERE IS SIGNIFICANT TRACK FORECAST SPREAD DRIVEN BY DIFFERING PREDICTIONS OF THE STORM STRUCTURE, COLD SURGE EVOLUTION, AND ADJUSTMENTS IN THE STEERING FLOW PATTERN. DIFFERENCES ARE EXEMPLIFIED BY THE ECMWF ENSEMBLE SOLUTIONS, WHICH INDICATE A WEST TO SOUTHWESTWARD TRACK GENERALLY CONSISTENT WITH THE CURRENT FORECAST AND GEFS ENSEMBLE SOLUTIONS, WHICH DEPICT A WEAKER SYSTEM TRACKING MORE SHARPLY TO THE SOUTHWEST. THE CURRENT FORECAST IS GENERALLY CONSISTENT WITH THE MULTI-MODEL CONSENSUS, WITH MEDIUM CONFIDENCE. AVAILABLE INTENSITY FORECAST GUIDANCE IS SUBJECT TO THE SAME UNCERTAINTIES THAT ARE INTRODUCING TRACK FORECAST UNCERTAINTY, BUT SLIGHT NEAR-TERM INTENSIFICATION FOLLOWED BY DISSIPATION AROUND TAU 72 ARE VERY LIKELY. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN