WDPN32 PGTW 042100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 28W (HALONG) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 24.9N 142.5E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 800 NM EAST OF KADENA AB MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS SIGNIFICANT WAVE HEIGHT: 17 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS RAPIDLY CYCLING DEEP CONVECTION, WITH THE BULK OF THE DEEP CONVECTION DISPLACED EAST OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 041558Z AMSR2 37GHZ IMAGE REVEALS SHALLOW CURVED BANDING WRAPPING OVER THE EASTERN AND NORTHERN QUADRANTS AROUND A WEAKLY-DEFINED LLCC. DEEP CONVECTION IS CONFINED TO THE EASTERN SEMICIRCLE AND IS ASSOCIATED WITH STRONGLY CONVERGENT SOUTHERLY LOW-LEVEL FLOW. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE AMSR2 IMAGE. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AGENCY DVORAK ESTIMATES OF T2.0 (30 KNOTS). INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: COMPETING STEERING PATTERN, WITH A SUBTROPICAL RIDGE (STR) TO THE WEST AND ANOTHER STR TO THE EAST. A NARROW, WEAK BREAK IN THE STR IS PRESENT TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T2.0 - 30 KTS KNES: T2.0 - 30 KTS CIMSS SATCON: 32 KTS AT 041553Z CIMSS ADT: 34 KTS AT 041730Z CIMSS AIDT: 35 KTS AT 041730Z CIMSS D-MINT: 31 KTS AT 041910Z CIMSS D-PRINT: 37 KTS AT 041900Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG EASTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 28W IS FORECAST TO TRACK SLOWLY WESTWARD THROUGH TAU 24 AS THE STR BUILDS TO THE NORTH. AFTER TAU 24, A SERIES OF MAJOR SHORTWAVE TROUGHS WILL PROPAGATE RAPIDLY THROUGH THE HIGH ZONAL MIDLATITUDE WESTERLIES. HOWEVER, THESE TROUGHS ARE LOCATED WELL NORTH OF 45N LATITUDE AND ARE NOT EXPECTED TO IMPACT THE STR OR TD 28W'S TRACK. CONSEQUENTLY, THE STR SHOULD REMAIN ENTRENCHED TO THE NORTH DRIVING TD 28W WESTWARD TO WEST- NORTHWESTWARD THROUGH TAU 96. AFTER TAU 96, THE SYSTEM WILL TRACK WEST-NORTHWESTWARD TO NORTHWARD. RAPID INTENSIFICATION (RI) IS HIGHLY PROBABLE AFTER TAU 24 DUE TO IMPROVING POLEWARD OUTFLOW, ESPECIALLY AFTER TAU 48 WITH VENTING INTO THE MIDLATITUDE WESTERLIES. MODEL DISCUSSION: TRACK CONFIDENCE THROUGH TAU 120 IS LOW DUE TO A MAJOR BIFURCATION IN THE DETERMINISTIC GUIDANCE. AVNI, JGSI AND AEMI RECURVE THE SYSTEM SHARPLY AND ARE LOCATED ON THE EASTERN SIDE OF THE AIDS ENVELOPE. ECMI, EEMI, NVGI, EGRI AND AFUI INDICATE A MORE WESTWARD TO WEST-NORTHWESTWARD TRACK AND ARE LOCATED ON THE WESTERN SIDE OF THE AIDS ENVELOPE. THERE IS AN UNUSUALLY LARGE SPREAD IN DETERMINISTIC GUIDANCE, WITH A 486NM CROSS-TRACK SPREAD AT TAU 72, 914NM CROSS-TRACK SPREAD AT TAU 96 AND 1517NM CROSS-TRACK SPREAD AT TAU 120. THE 041200Z ECMWF ENSEMBLE (EPS) ALSO SHOWS A SIMILAR LARGE SPREAD REFLECTING THE HIGH DEGREE OF UNCERTAINTY IN THE JTWC TRACK FORECAST, WITH THE MAJORITY OF SOLUTIONS EVENTUALLY RECURVING THE SYSTEM POLEWARD BETWEEN 115-137E LONGITUDE. THUS FAR, THERE HAVE BEEN ONLY TWO RUNS OF AVNI, AEMI AND JGSI, AND THEY HAVE BEEN EXTREMELY ERRATIC. ADDITIONALLY, GFS IS DRIVING THE SYSTEM THROUGH THE STR WITH NO DYNAMIC SHORTWAVE TROUGH PRESENT, WHICH IS UNLIKELY. IN GENERAL, THE JTWC TRACK FORECAST FAVORS THE ECMWF SOLUTION, WITH A FLATTER TRACK SUPPORTED BY PERSISTENT RIDGING TO THE NORTH AND A HIGH ZONAL MIDLATITUDE PATTERN. FORECAST CONFIDENCE: TRACK 00-72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN