WDPN31 PGTW 042100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 05W (AERE) WARNING NR 018// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 32.8N 129.4E INITIAL INTENSITY: 25 KTS GEOGRAPHIC REFERENCE: 23 NM SOUTHWEST OF SASEBO, JAPAN MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 13 KTS SIGNIFICANT WAVE HEIGHT: 10 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH WEAKENING CONVECTION SHEARED WELL TO THE SOUTHEAST OVER WESTERN KYUSHU, UNDER THE INFLUENCE OF PERSISTENT NORTHWESTERLY UPPER-LEVEL FLOW. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE SUPPORTED BY THE RJTD AND PGTW POSITION FIXES, ANIMATED RADAR DATA FROM JMA SHOWING THE LOW LEVEL RAIN BANDS, AND IN THE CENTER OF THE EXPOSED LLCC IN ANIMATED SHORTWAVE INFRARED SATELLITE IMAGERY. THE INITIAL INTENSITY OF 25 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE. SURFACE OBSERVATIONS FROM THE REGION INDICATE LIGHT WINDS OF LESS THAN 10 KNOTS, BUT MSLP READINGS FROM NAGASAKI AND FUKUE INDICATE PRESSURES OF 1000MB, WHICH SUPPORTS A 997MB ASSESSED CENTRAL PRESSURE. THE WIND PRESSURE RELATIONSHIP ALONE WOULD SUGGEST A 30-35 KNOT INTENSITY, HOWEVER A PREVIOUS PARTIAL ASCAT-C PASS FROM 041314Z SHOWED MAXIMUM WINDS OF ONLY 15-20 KNOTS, THUS THE INITIAL INTENSITY REMAINS SET AT 25 KNOTS. ANIMATED WATER VAPOR IMAGERY INDICATES THE UPPER-LEVEL LOW THAT PREVIOUSLY WAS ENSCONCED OVER THE SYSTEM HAS MOVED AWAY AND HAS BEEN REPLACED BY A SHARP UPPER-LEVEL TROUGH, THE AXIS OF WHICH IS CURRENTLY MOVING OVER THE SYSTEM, INDUCING NORTHWESTERLY, CONVERGENT FLOW OVER THE SYSTEM. THE ENVIRONMENT IS BECOMING STEADILY LESS FAVORABLE, WITH MODERATE TO HIGH VWS AND LAND INTERACTION ADDING TO THE ALREADY UNFAVORABLE SUBSIDENCE ALOFT. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T2.0 - 30 KTS CIMSS SATCON: 47 KTS AT 041733Z CIMSS ADT: 45 KTS AT 041740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE VWS: 20-25 KTS SST: 26-27 CELSIUS OUTFLOW: WEAK EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH 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: THE FORECAST EVOLUTION OF TD 05W IS COMPLEX. IN THE NEAR-TERM (NEXT 24 HOURS), THE SYSTEM IS FORECAST TO TRACK EAST-NORTHEASTWARD ALONG THE NORTHERN PERIPHERY OF THE STR SLIDING WESTWARD ALONG THE 25TH PARALLEL, TD 05W WILL MOVE AT A RELATIVELY QUICK PACE, CROSSING NORTHERN KYUSHU AND THE INLAND SEA BEFORE EMERGING BACK OVER WATER SOUTH OF TOKYO BY TAU 36. AT THIS POINT THINGS GET COMPLICATED. GLOBAL MODELS SUGGEST A WEAK BAROCLINIC LOW WILL DEVELOP IN THE VICINITY OF TOKYO AROUND TAU 24 AT THE TAIL END OF A 500MB TROUGH AND MOVE OFFSHORE. BY TAU 36, THE VORTICITY ASSOCIATED WITH TD 05W OR ITS REMNANTS ARE EXPECTED TO MERGE WITH THIS LOW PRESSURE AREA. INITIALLY THE BAROCLINIC ENERGY ASSOCIATED WITH THE 500MB SHORTWAVE TROUGH WILL GIVE A BOOST TO TD 05W, ALLOWING FOR REINTENSIFICATION OF THE SYSTEM. SIMULTANEOUSLY IN THE UPPER LEVELS, A HIGH-AMPLITUDE RIDGE EXTENDS NORTH FROM JAPAN INTO THE SEA OF OKHOTSK, LEADING TO DEVELOPMENT OF A CUTOFF LOW OVER TD 05W. ULTIMATELY THIS FORMS A REX BLOCK WITH TD 05W LYING UNDERNEATH THE WARM-CORE CUTOFF LOW TO THE SOUTH WITH A UPPER-LEVEL ANTICYCLONE TO THE NORTH OVER THE SEA OF OKHOTSK. THIS PATTERN IS EXPECTED TO REMAIN IN PLACE THROUGH AT LEAST TAU 72, AND TD 05W WILL BECOME QUASI-STATIONARY TO THE EAST OF HONSHU DURING THIS TIMEFRAME UNDER THE INFLUENCE OF A WEAK STEERING PATTERN. BY TAU 96 THE REX BLOCK BEGINS TO BREAK DOWN, WITH THE STR TO THE EAST BUILDING AND REORIENTING TO A MORE NORTH-SOUTH AXIS, EJECTING TD 05W TO THE NORTH-NORTHWEST. TD 05W IS FORECAST TO INTENSIFY TO A PEAK OF 35 KNOTS AS IT MOVES EAST OF HONSHU, THEN SLOWLY WEAKEN THROUGH THE END OF THE FORECAST PERIOD. THE SYSTEM WILL BEGIN SUBTROPICAL TRANSITION BY TAU 48 AS IT MOVES UNDER THE UPPER-LEVEL CUTOFF LOW, AND FULLY TRANSITION TO A GALE-FORCE SUBTROPICAL LOW NO LATER THAN TAU 96. MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN RELATIVELY GOOD AGREEMENT THROUGH 72 AS THE SYSTEM TRACKS ALONG THE NORTHERN EDGE OF THE STR. MODEL SPREAD IS 145NM AT TAU 72 WITH THE JGSM MARKING THE SOUTHERN EDGE OF THE ENVELOPE AND NAVGEM THE NORTHERN. WHILE THE GUIDANCE AGREES ON THE OVERALL SCENARIO IN THE LONG-RANGE FORECAST, AVAILABLE GUIDANCE SHOWS SIGNIFICANT DISAGREEMENT IN BOTH THE TIMING OF THE EJECTION NORTHWARD AND THE DIRECTION OF MOTION ONCE TD 05W MOVES POLEWARD. CROSS-TRACK SPREAD INCREASES TO 280NM WHILE ALONG-TRACK SPREAD INCREASES TO 350NM BY TAU 120, WITH THE ECMWF, ITS ENSEMBLE AND NAVGEM RACING THE SYSTEM NORTHWARD AT OVER 20 KNOTS WHILE THE REMAINDER OF THE GUIDANCE SUGGESTS A WEAKER STEERING GRADIENT WITH THE SYSTEM MOVING POLEWARD AT A MUCH SLOWER PACE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THOUGH TAU 36 AS THE SYSTEM MOVES OVER LAND, BUT ONCE THE SYSTEM IS BACK OVER WATER AND BEGINS TO UNDERGO SUBTROPICAL TRANSITION, THE GUIDANCE SHOWS INCREASING UNCERTAINTY. ALL MODELS AGREE ON INTENSIFICATION BUT DIFFER IN THE AMOUNT, DEPENDENT UPON THE DEGREE OF INTERACTION WITH THE UPPER-LEVEL TROUGH AND LOW. SHIPS SUGGEST DISSIPATION AFTER TAU 48, WHILE COAMPS-TC AND HWRF BRING THE INTENSITY UP TO 45 KNOTS AT TAU 48 WITH SLOW WEAKENING THEREAFTER. THE JTWC FORECAST IS WITHIN 5 KNOTS OF THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD. CONFIDENCE IS HIGH THROUGH TAU 72, BUT MEDIUM IN THE EXTENDED PERIOD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: HIGH INTENSITY 72-120 HR: MEDIUM// NNNN