WDPN31 PGTW 232100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 02W (SEPAT) WARNING NR 006// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 28.4N 141.9E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 218 NM NORTH OF IWO TO MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 17 KTS SIGNIFICANT WAVE HEIGHT: 17 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT SYSTEM CHARACTERIZE BY WELL-DEFINED LOW-LEVEL BANDING FEATURES. DURING THE OVERNIGHT HOURS, A BRIEF PERIOD OF ENHANCED POLEWARD OUTFLOW, SUPPORTED BY THE TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL TO THE SOUTHWEST, ALLOWED THE LOW LEVEL CIRCULATION CENTER (LLCC) TO ALIGN WITH CONVECTION LEADING TO A BRIEF INTENSIFICATION OF TS 02W. OVER THE PAST COUPLE OF HOURS, CONVECTION HAS LARGELY DISSIPATED, REVEALING THE INNER, LOW-LEVEL STRUCTURE. IN THE LAST HOUR HOWEVER, EIR IMAGERY INDICATES CONVECTION REFORMING IN CLOSE PROXIMITY TO THE LLCC. A 231552Z AMSR2 COLOR ENHANCED 89GHZ MICROWAVE IMAGE INDICATED SIGNIFICANT SOUTHERLY SHEAR, WITH THE UPPER-LEVEL CONVECTION AND VORTEX DISPLACED ABOUT 30NM NORTH OF THE LOW-LEVEL VORTEX CENTER. EARLIER ASCAT DATA FROM AROUND 1400Z INDICATED A WELL-DEFINED LLCC, AND 35-40 KNOT SURFACE WINDS EXTENDING OUTWARD ABOUT 100NM IN THE EASTERN HEMISPHERE OF THE CIRCULATION, WITH THE MAJORITY OF THE ELEVATED WINDS TO BE FOUND IN THE NORTHEASTERN SECTOR. THE ENVIRONMENT IS MARGINAL. WHILE SSTS REMAIN WARM, AND DEEP-LAYER SHEAR REMAINS LOW, THE UPPER-LEVEL PATTERN IS EVOLVING. THE TUTT MOVING AWAY TO THE SOUTHWEST AND THE SYSTEM MOVING UNDER A COL-REGION, RESULTING IN REDUCED OUTFLOW ALOFT AND MODERATE MID-LEVEL SOUTHERLY SHEAR. INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SCATTEROMETER DATA. CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED IN THE NORTHERN PACIFIC. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS RCTP: T2.0 - 30 KTS KNES: T3.0 - 45 KTS CIMSS SATCON: 44 KTS AT 231500Z CIMSS ADT: 35 KTS AT 231730Z CIMSS AIDT: 37 KTS AT 231730Z CIMSS D-MINT: 31 KTS AT 231554Z CIMSS D-PRINT: 31 KTS AT 231830Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 5-10 KTS SST: 27-28 CELSIUS OUTFLOW: WEAK POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THE END-PHASE TRANSITION HAS BEEN CHANGED FROM A DISSIPATION SCENARIO TO AN EXTRATROPICAL TRANSITION (ETT) SCENARIO. FORECAST DISCUSSION: TS 02W IS PROJECTED TO CONTINUE TRACKING TOWARDS THE NORTHWEST OVER THE NEXT 24 HOURS, STEERED BY THE SOUTHWESTERN PERIPHERY OF THE STEERING RIDGE LOCATED IN THE NORTHERN PACIFIC. BY TAU 24 THE SYSTEM WILL APPROACH THE RIDGE AXIS, SLOWING DOWN A COUPLE OF KNOTS BETWEEN TAU 24 AND TAU 36 AS IT MOVES ACROSS THE RIDGE AXIS. SUBSEQUENTLY, IT WILL ACCELERATE ONCE AGAIN AS IT TURNS NORTHEASTWARD. THE CENTER OF THE TS 02W IS EXPECTED TO CLIP THE SOUTHERN AND EASTERN EDGE OF THE BOSO PENINSULA BETWEEN TAUS 36 AND 48 BEFORE ACCELERATING FURTHER INTO THE OPEN WATERS OFF EASTERN HONSHU THROUGH THE REMAINDER OF THE FORECAST PERIOD. REGARDING INTENSITY, WITH THE RENEWED DEVELOPMENT OF DEEP CONVECTION, SLIGHT INTENSIFICATION IS POSSIBLE OVER THE NEXT FEW HOURS, THOUGH THIS IS NOT SPECIFICALLY CAPTURED IN THE FORECAST. AS THE SYSTEM MOVES FURTHER POLEWARD OVER THE NEXT 12 TO 24 HOURS, IT WILL ENCOUNTER AN INCREASINGLY UNFAVORABLE UPPER-LEVEL ENVIRONMENT. THE 200MB WINDS WILL SHIFT TO NORTHWESTERLY, INDUCING CONVERGENT FLOW ALOFT AND DEPRIVING THE SYSTEM OF SIGNIFICANT OUTFLOW ALOFT. AS THE WEAKENED VORTEX APPROACHES THE JAPANESE COAST, IT WILL MOVE NORTH OF THE 26C ISOTHERM AND BEGIN THE EARLY PHASE OF EXTRATROPICAL TRANSITION (ETT) AS IT BEGINS TO INTERACT WITH AN APPROACHING MID-LATITUDE SYSTEM MOVING EASTWARD ACROSS THE SEA OF JAPAN. AS THE SYSTEM MAKES ITS CLOSEST APPROACH TO YOKOSUKA, IT WILL HAVE BE A RELATIVELY SHALLOW SYSTEM, WITH 30KT WINDS CONFINED TO THE EASTERN HEMISPHERE OF THE SYSTEM. ETT IS EXPECTED TO BE COMPLETED NO LATER THAN TAU 72 TS 02W PUSHES NORTHEASTWARD INTO THE WESTERN PACIFIC. TS 02W WILL BE WEAKENING AS IT UNDERGOES ETT, AND IT IS POSSIBLE THAT IT DISSIPATES BELOW THE 25 KNOT WARNING THRESHOLD PRIOR TO COMPLETING THE ETT. MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE SHOW STRONG AGREEMENT, WITH MINIMAL CROSS- OR ALONG-TRACK SPREAD THROUGH TAU 48. MODELS BEGIN TO DIVERGE AFTER THE SYSTEM ROUNDS THE RIDGE AXIS WITH SPREAD INCREASING TO OVER 250NM IN BOTH AXES BY THE END OF THE FORECAST PERIOD. THE JTWC FORECAST IS POSITIONED TO THE WEST OF THE MULTI-MODEL CONSENSUS MEAN, CLOSELY ALIGNING TO THE ECMWF DETERMINISTIC TRACKER FOR THE ENTIRE FORECAST PERIOD. A NOTABLE EXCEPTION TO THE TIGHT GUIDANCE GROUPING IS THE ECMWF-AIFS MODEL, WHICH TAKES THE REMNANT VORTEX NORTH TOWARDS MISAWA AFTER TAU 48. INTENSITY GUIDANCE IS FOR THE MOST PART IN GOOD AGREEMENT AS WELL, WITH THE EXCEPTION OF THE DECAY-SHIPS (BOTH GFS AND NAVGEM) WHICH INDICATE NEAR-TERM INTENSIFICATION TO NEAR 50 KNOTS. THE REMAINDER OF THE GUIDANCE PACKAGE SHOWS A SLOW BUT STEADY WEAKENING THROUGH THE FORECAST, WITH PERIODS OF STEADY-STATE INTENSITY, PARTICULARLY OVER THE NEXT 36 HOURS. THE JTWC FORECAST IS SET SLIGHTLY LOWER THAN THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN