WDPN31 PGTW 030300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 006// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 27.0N 145.4E INITIAL INTENSITY: 45 KTS GEOGRAPHIC REFERENCE: 577 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 18 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM (TS) 04W (MUN) HAS UNDERGONE A RATHER REMARKABLE TRANSFORMATION OVER THE LAST SIX HOURS. AT THE PREVIOUS FORECAST TIME, THE LOW LEVEL CIRCULATION CENTER (LLCC) WAS JUST BEGINNING TO TUCK UNDER RECENTLY DEVELOPED CONVECTION. BASED ON A SERIES OF MICROWAVE IMAGES FROM THE COWVR AND WSF-M INSTRUMENTS, THE LLCC APPEARS TO HAVE UNDERGONE A PRECESSION, AS VORTEX AXISYMMETRIZED UNDER THE CONVECTIVE REGION. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THE CONVECTION HAS WARMED SIGNIFICANTLY OR DISSIPATED ALL TOGETHER IN THE PAST COUPLE OF HOURS, LEAVING A HOW MOSTLY EXPOSED LLCC, WITH POCKETS OF REFORMING DEEP CONVECTION. THE UPPER-LEVEL STRUCTURE IS COMPLEX BASED ON CIRA UPPER-LEVEL DERIVED MOTION VECTORS (ULDMV), SHOWING AN ANTICYCLONIC ARC OF OUTFLOW PUSHING SOUTH, THEN TURNING POLEWARD ALONG THE WESTERN EXTENT OF THE CIRCULATION. MEANWHILE UPPER-LEVEL FLOW IS CYCLONIC ALONG THE EASTERN SIDE OF THE VORTEX UNTIL REACHING A POINT NORTH OF 30N WHERE IT TURNS ANTICYCLONICALLY. THE CIRA ADVECTED LAYER PRECIPITABLE WATER PRODUCT DEPICTS A WEDGE OF DEEP, DRY AIR MOVING UP FROM THE SOUTH AND WRAPPING ALL THE WAY AROUND THE VORTEX, ENCROACHING INTO THE INNER-CORE. OVERALL, THE ENVIRONMENT IS FAVORABLE, WITH WARM SSTS, GOOD OUTFLOW ALOFT AND LOW VWS, THOUGH OFFSET SOMEWHAT BY THE INFLUENCE OF THE DRY AIR. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF AN EXTENSIVE RIDGING PATTERN EXTENDING FROM EAST OF THE PHILIPPINES, OVER THE MARIANAS ISLANDS AND THEN NORTHEASTWARD TO NEAR 35N 175E. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T2.0 - 30 KTS RCTP: T2.5 - 35 KTS KNES: T3.0 - 45 KTS CIMSS SATCON: 46 KTS AT 030000Z CIMSS ADT: 35 KTS AT 030000Z CIMSS AIDT: 39 KTS AT 030000Z CIMSS D-MINT: 33 KTS AT 022052Z CIMSS D-PRINT: 37 KTS AT 030030Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 27-28 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: DRY MID-LEVEL AIR WRAPPING INTO THE CORE OF THE SYSTEM. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: DUE TO VORTEX PRECESSION, TS 04W HAS SLOWED CONSIDERABLY OVER THE PAST SIX HOURS. NOW THAT THE VORTEX APPEARS TO BE VERTICALLY ALIGNED, THE SYSTEM WILL BEGIN TO ACCELERATE TOWARDS THE NORTH-NORTHWEST IN THE NEAR-TERM, ALONG THE WESTERN SIDE OF THE STEERING RIDGE TO THE EAST. BY TAU 36, THE SOUTHWESTERN END OF THE LARGE RIDGING PATTERN BREAKS OFF INTO A DISTINCT SUBTROPICAL RIDGE (STR) CENTER OVER THE NORTHERN MARIANAS. AS THIS STR BUILDS AND EXPANDS IN AREAL COVERAGE, IT WILL BECOME THE DOMINANT STEERING INFLUENCE OF TS 04W, WHICH WILL TURN ONTO A MORE EAST-NORTHEASTWARD TRACK BETWEEN TAU 36 AND TAU 72. BEYOND TAU 72, THE SYSTEM WILL TURN NORTHWARD, TRAVERSING ALONG THE WESTERN SIDE OF A DEVELOPING REX BLOCK SETTING UP ALONG 165E. AFTER TAU 96, TS 04W WILL ACCELERATE INTO A DEVELOPING BREAK IN THE RIDGE TO THE NORTH. IN TERMS OF INTENSITY, THE SYSTEM HAS ENJOYED A BRIEF SPURT OF INTENSIFICATION DUE TO THE VORTEX ALIGNMENT. HOWEVER, THE INFLUENCE OF DRY AIR ON THE INNER-CORE WILL PUT A BRAKE ON THE INTENSIFICATION TREND IN THE NEAR-TERM. UNTIL THE CONVECTION CAN PERSIST IN AND AROUND THE CORE AND PUSH THE DRY AIR OUT, THE SYSTEM WILL INTENSIFY AT A SLOW BUT STEADY RATE. THIS PROCESS SHOULD BE WRAPPED UP AROUND TAU 36, AT WHICH POINT, THE SYSTEM WILL ALSO TAP INTO AN ENHANCED POLEWARD OUTFLOW CHANNEL ON THE SOUTHEAST SIDE OF AN UPPER-LEVEL TROF APPROACHING FROM THE NORTHWEST. THIS WILL ALLOW FOR ANOTHER BURST OF MORE PROLONGED INTENSIFICATION THROUGH TAU 72. A SHARP INCREASE IN SHEAR IS ANTICIPATED TO HIT THE SYSTEM BETWEEN TAU 72 AND 96, WITH TS 04W LIKELY BEING DECAPITATED AROUND TAU 96, AS IT ALSO HAPPENS TO CROSS THE 26C ISOTHERM. THE SYSTEM IS EXPECTED TO REMAIN WARM-CORE EVEN AS IT RAPIDLY SHALLOWS OUT, BEGINNING SUBTROPICAL TRANSITION (STT) BETWEEN TAU 96-120 AS IT RAPIDLY WEAKENS. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS BY AND LARGE IN GOOD AGREEMENT ON THE OVERALL S-TYPE TRACK SCENARIO. THE GALWEM CONTINUES TO DEPART FROM THE REST OF THE GUIDANCE, IN BEING SIGNIFICANTLY SLOWER AND THEN TRACKING NORTHWEST TOWARDS HONSHU AFTER TAU 96. THE HWRF AND HAFS-A (THOUGH NOT MEMBERS OF THE TRACK CONSENSUS) SHOW A SIMILAR TREND, THOUGH THEY ARE MORE IN LINE WITH THE REST OF THE GUIDANCE IN TERMS OF SPEED THROUGH TAU 72. THE REMAINDER OF THE CONSENSUS PACKAGE IS CONFINED TO A 120NM ENVELOPE THROUGH TAU 72 AND THE JTWC TRACK IS POSITIONED JUST EAST OF THE CONSENSUS MEAN. AFTER TAU 72, THE MODELS BEGIN TO DISPERSE AND FAN OUT, WITH THE ECMWF SHOWING THE FURTHEST WEST TRACK, WHILE THE NAVGEM IS THE FURTHEST TO THE EAST. THE JTWC TRACK IS POSITIONED JUST EAST OF THE CONSENSUS MEAN. ENSEMBLE GUIDANCE IS ALSO IN GENERAL AGREEMENT, THOUGH THERE REMAIN FIVE ECEPS MEMBERS AND TEN GEFS MEMBERS WHICH DEPICT A TRACK TOWARDS HONSHU, THUS THERE IS A VERY LOW, BUT NON-ZERO, PROBABILITY OF A POTENTIAL WESTWARD TRACK AFTER TAU 72. INTENSITY GUIDANCE IS MIXED, WITH THE HAFS-A AND HWRF INDICATING A FLAT OR DECREASING TREND THROUGH TAU 48, THEN A SHARP INCREASE TO A PEAK BETWEEN 55-70 KNOTS AT TAU 72 FOLLOWED BY RAPID WEAKENING. THE CTCX MEANWHILE INDICATES SLOW INTENSIFICATION TO TAU 24, THEN RAPID UP TO A PEAK OF 80 KNOTS AT TAU 60. THREE RAPID INTENSIFICATION (RI) AIDS HAVE TRIPPED (RICN, RIDE AND FRIA) ON THIS CYCLE, AND THE CTCX ENSEMBLE INDICATES A THIRTY PERCENT PROBABILITY OF RI IN THE TAU 48-72 TIMEFRAME. THUS, THERE IS A LOW PROBABILITY OF A NEAR-TERM RI EVENT. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN