WDPN31 PGTW 090300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15E (NOLO) WARNING NR 074// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 28.2N 149.8E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 680 NM SOUTHEAST OF TOKYO, JAPAN MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS SIGNIFICANT WAVE HEIGHT: 26 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TS 15E HAS MAINTAINED INTENSITY OVER THE PAST SIX HOURS WILL SUPPORT FROM FAVORABLE UPPER-LEVEL FLOW AND PASSAGE OVER WARM WATER. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS LIMITED, PATCHY DEEP CONVECTION OVER A WELL-DEFINED LOW-LEVEL CIRCULATION AND STRATOCUMULUS CLOUD LINES TRACING A DRIER AIR MASS TO THE WEST OF THE CIRCULATION, WHICH MAY ALREADY BE INFLUENCING THE SYSTEM. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON TIGHTLY-GROUPED SATELLITE FIXES FROM PGTW, RJTD, AND RCTP AND ON A CLEAR CENTER FEATURE EVIDENT UPSTREAM IN A 082018Z WSF-M PASS. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE CONSISTENT WITH THE HIGH END OF SUBJECTIVE DVORAK AND AUTOMATED INTENSITY ESTIMATES LISTED BELOW. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK AND PERSISTENCE CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE EAST-NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T3.0 - 45 KTS RCTP: T3.0 - 45 KTS CIMSS ADT: 33 KTS AT 082350Z CIMSS D-MINT: 46 KTS AT 082339Z CIMSS D-PRINT: 41 KTS AT 090110Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 10-15 KTS SST: 27-28 CELSIUS OUTFLOW: MODERATE POLEWARD AND EQUATORWARD OTHER FACTORS: ENTRAINMENT OF DRIER AIR FROM THE WEST ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: FORECAST INTENSITIES HAVE DECREASED SLIGHTLY FROM THE PREVIOUS WARNING. OTHERWISE, THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 15E WILL TURN POLEWARD AND EASTWARD AROUND THE WESTERN PERIPHERY OF THE CURRENT STEERING RIDGE DURING THE 72 HOUR FORECAST PERIOD. THE SYSTEM IS EXPECTED TO INTERACT WITH A SHALLOW SHORTWAVE TROUGH APPROACHING FROM THE WEST AND COMPLETE EXTRATROPICAL TRANSITION AFTER TAU 48. FAVORABLE UPPER-LEVEL SUPPORT AND PASSAGE OVER WARM WATER WILL ALLOW TS 15E TO MAINTAIN INTENSITY AS A MID-RANGE TROPICAL STORM OVER THE NEXT 24 HOURS, WITH THE POTENTIAL FOR A SMALL TERM BOOST BY TAU 24. THEREAFTER, THE SYSTEM WILL ENCOUNTER INCREASING VERTICAL WIND SHEAR AND ENTRAINMENT OF DRIER AIR FROM THE WEST WILL INCREASE SIGNIFICANTLY AS IT ROUNDS THE STEERING RIDGE AXIS, DRIVING A STEADY WEAKENING TREND. BAROCLINIC SUPPORT SHOULD BE SUFFICIENT TO ALLOW THE SYSTEM TO MAINTAIN TROPICAL DEPRESSION LEVEL INTENSITY AS IT COMPLETES EXTRATROPICAL TRANSITION. MODEL DISCUSSION: NUMERICAL MODEL TRACK AND INTENSITY FORECAST GUIDANCE ARE BOTH IN GOOD AGREEMENT REGARDING THE OVERALL SCENARIO, INCLUDING A TIGHT TURN AROUND THE STEERING RIDGE AND SLIGHT NEAR-TERM INTENSIFICATION FOLLOWED BY WEAKENING AFTER TAU 24. PHYSICS-BASED MODELS DEPICT A WIDER AND SLOWER TURN THAN THE AI-BASED MODELS, RESULTING IN SIGNIFICANT CROSS-TRACK AND ALONG-TRACK SPREAD BY TAU 72. THE CURRENT TRACK FORECAST HOLDS STEADY WITH THE PREVIOUS JTWC FORECAST, SET JUST SLIGHTLY TO THE WEST AND MORE CONSISTENT WITH THE AI-BASED MODELS. ADDITIONAL ADJUSTMENTS MAY BE NECESSARY ON SUBSEQUENT FORECASTS UNTIL GUIDANCE COMES INTO BETTER ALIGNMENT, AND CONFIDENCE CAN ONLY BE CHARACTERIZED AS MEDIUM AT THIS POINT. THE INTENSITY FORECAST IS CONSISTENT WITH CONSENSUS GUIDANCE, WHICH HAS DROPPED A BIT SINCE THE PREVIOUS FORECAST CYCLE. GIVEN TRENDS IN SATELLITE PRESENTATION AND MODEL GUIDANCE, DISSIPATION OF THE CIRCULATION PRIOR TO EXTRATROPICAL TRANSITION IS NOW A POSSIBILITY, ALTHOUGH IT IS THE LESS LIKELY SCENARIO. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM// NNNN