WDPN31 PGTW 022100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 26.8N 145.6E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 593 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM (TS) 04W (MUN) EXHIBITS A LOPSIDED APPEARANCE IN THE LATEST ANIMATED ENHANCED INFRARED (EIR) SATELLITE LOOP. DEEP CONVECTION HAS FLARED WEST OF THE PREVIOUSLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) OVER THE PAST FEW HOURS. BASED ON THE LATEST CIRA UPPER-LEVEL DERIVED MOTION VECTOR (ULDMV) PRODUCT, THE ASSOCIATED OUTFLOW HAS STARTED TO PUSH EASTWARD AGAINST THE PREVAILING SOUTHWESTERLY UPPER-LEVEL FLOW, CREATING AN OPPORTUNITY FOR THE LLCC TO RE-ALIGN WITH THE CONVECTION. THOUGH HARD TO DEFINITIVELY DETERMINE WITHOUT RECENT MICROWAVE IMAGERY, THE STRONGEST UPDRAFTS AND COLDEST CLOUD TOPS ARE STILL NOT VERTICALLY ALIGNED WITH THE LLCC DUE TO SOME MID-LEVEL NORTHEASTERLY SHEAR. A 021546Z AMSR2 89GHZ MICROWAVE IMAGE CAPTURED THE SETUP PRIOR TO THE LLCC MOVING UNDER THE CONVECTION, WITH THE VORTEX REMAINING THE DRY, RELATIVELY CLEAR AIR TO THE EAST OF THE CONVECTIVE ACTIVITY. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON EXTRAPOLATION OF THE AMSR2 IMAGE, AS WELL AS TRACKING OF THE VORTEX IN ANIMATED SHORTWAVE INFRARED (SWIR) IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION OF AN EARLIER ASCAT PASS, AS WELL AS THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES NOTED ABOVE. THE ENVIRONMENT IS STEADILY IMPROVING, NOW THAT THE TUTT-CELL HAS STARTED TO MOVE AWAY AND DISSIPATE, OPENING UP A MUCH STRONGER, DIVERGENT POLEWARD OUTFLOW CHANNEL AND SSTS REMAIN SUFFICIENTLY WARM TO SUPPORT DEVELOPMENT. THE MAIN HINDRANCE AT THE MOMENT REMAINS THE SIGNIFICANT WEDGE OF DRY AIR, EVIDENT IN THE TOTAL PRECIPITABLE WATER (TPW) LOOP, EXTENDING NORTHWARD ALONG THE EASTERN PERIPHERY OF THE VORTEX. THE LATEST SOUNDING FROM CHICHIJIMA, ON THE WESTERN EDGE OF THE CONVECTIVE SHIELD, INDICATES THIS DRY MID-LEVEL AIR EXTENDS OUT TO THE WEST AS WELL, SUCH THAT TS 04W IS COCOONED IN A VERY SMALL POCKET OF RELATIVELY MOIST AIR. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: WEST-NORTHWEST PERIPHERY OF AN ELONGATED RIDGING PATTERN EXTENDING FROM SOUTHWEST OF GUAM NORTHEASTWARD TO 40N 178E. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS KNES: T2.0 - 30 KTS CIMSS ADT: 35 KTS AT 021730Z CIMSS AIDT: 41 KTS AT 021730Z CIMSS D-PRINT: 36 KTS AT 021820Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 15-20 KTS SST: 27-28 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: DRY MID-LEVEL AIR IN THE EASTERN PORTION OF THE SYSTEM. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: ADDED SUBTROPICAL TRANSITION AT THE END OF THE FORECAST. FORECAST DISCUSSION: TS 04W IS EXPECTED TO FOLLOW A CLASSIC S-TYPE TRACK, OFTEN ASSOCIATED WITH A REVERSE-ORIENTED MONSOON TROF SETUP, THROUGHOUT THE FORECAST PERIOD. IN THE NEAR-TERM, TS 04W WILL CONTINUE TRACKING NORTH-NORTHWEST TO NORTH OVER THE NEXT 24 TO 36 HOURS, ALONG THE WESTERN SIDE OF AN EXTENSIVE RIDGING PATTERN THAT EXTENDS FROM SOUTHWEST OF GUAM ALL THE WAY TO 40N NEAR THE DATELINE. THE SOUTHWESTERN PORTION OF THIS RIDGE COMPLEX IS FORECAST TO BUILD SIGNIFICANTLY AFTER TAU 24, AND BY TAU 48, A VERY LARGE AND VERY STRONG SUBTROPICAL RIDGE (STR) WILL DEVELOP OVER THE NORTHERN MARIANAS. SIMULTANEOUSLY, AN UPPER-LEVEL TROF WILL MOVE FROM WEST-EAST TO THE NORTH OF TS 04W, ERODING AND PUSHING THE NORTHERN PORTION OF THE RIDGE FURTHER EAST. THIS WILL ALLOW TS 04W TO QUICKLY TRANSITION TO A MORE EAST-NORTHEASTWARD TRACK AFTER TAU 36. BEYOND TAU 60, THE OPPOSITE PATTERN BEGINS TO TAKE SHAPE, WITH THE STR PUSHING WEST INTO THE PHILIPPINE SEA, WHILE THE RIDGE TO THE NORTHEAST OF TS 04W BEGINS TO BUILD, WITH THE GFS INDICATING DEVELOPMENT OF REX BLOCK PATTERN NEAR THE DATELINE. AS THIS RIDGE BUILDS AND ORIENTS ALONG A NORTH-SOUTH AXIS, TS 04W WILL TURN POLEWARD AFTER TAU 72, TURNING NORTHWESTWARD BY THE END OF THE FORECAST PERIOD AS THE RIDGE CONTINUES TO BUILD AND SHIFT WEST. IN TERMS OF INTENSITY, THE PERSISTENT DRY AIR TO THE EAST WILL INHIBIT SIGNIFICANT INTENSIFICATION IN THE NEAR-TERM, EVEN IF THE CURRENT CONVECTIVE BURST CAN PERSIST. THE MAJORITY OF THE MODELS DEPICT A STEADY MOISTENING OF THE ENVIRONMENT BEGINNING AROUND TAU 24, WHICH WILL ALLOW FOR A SLOW INTENSIFICATION TREND TO ABOUT TAU 48. THE APPROACH OF AN UPPER-LEVEL TROF AROUND TAU 48 WILL LEAD TO IMPROVED POLEWARD AND EASTWARD OUTFLOW, AND TS 04W IS EXPECTED TO INTENSIFY FAIRLY QUICKLY THROUGH TAU 72 UNDER THESE MORE FAVORABLE CONDITIONS. SHORTLY AFTER TAU 72 HOWEVER, ANOTHER, MUCH STRONGER TROF AND ASSOCIATED DEFORMATION ZONE WILL PUSH DOWN OVER TS 04W, INTRODUCING SIGNIFICANT NORTHEASTERLY SHEAR WHICH WILL START THE WEAKENING TREND. AS THE SYSTEM PASSES 35N, IT WILL MOVE INTO COOLER WATERS, INGEST SIGNIFICANT DRY AIR INTO THE VORTEX AND CONTINUE TO SUFFER THE EFFECTS OF STRONG SHEAR, STEADILY WEAKENING THROUGH THE END OF THE FORECAST. THE SYSTEM IS EXPECTED TO REMAIN WARM-CORE THROUGHOUT THE FORECAST PERIOD, THOUGH AS IT SHALLOWS OUT, WILL SLOWLY BEGIN TO TRANSITION TO A SUBTROPICAL LOW AFTER TAU 96. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GENERAL AGREEMENT ON THE OVERALL S-TYPE TRACK SCENARIO, THOUGH MODEL SPREAD IS SIGNIFICANT. AS EARLY AS TAU 24, THE GFS AND GEFS BEGIN TO DIVERGE FROM THE REMAINDER OF THE MODEL PACKAGE, WITH A SHARPER EASTWARD TURN, TRACK THE SYSTEM EAST ROUGHLY ALONG 30N. THE REMAINDER OF THE GUIDANCE IS CLOSELY PACKED ABOUT THE MEAN, WITH A CONSISTENT CROSS-TRACK SPREAD OF ABOUT 130NM FROM TAU 36 TO TAU 72, BETWEEN THE EGRR ON THE LEFT SIDE AND GFS ON THE RIGHT SIDE OF THE ENVELOPE. THE JTWC FORECAST IS POSITIONED CLOSE TO THE CONSENSUS MEAN AND ECMWF TRACKER THROUGH TAU 72. AFTER TAU 72, THE GFS AND GEFS REJOIN THE ECMWF, EGRR AND ECMWF ENSEMBLE IN TRACKING THE SYSTEM NORTH, THEN NORTHWESTWARD, WHILE THE NAVGEM, JGSM AND THE EC-AIFS PUSH THE SYSTEM STRAIGHT NORTH-NORTHEASTWARD. THE JTWC FORECAST IS POSITIONED EAST OF THE TIGHTEST GROUPING OF MODELS BUT FOLLOWS THE OVERALL SHAPE OF THE TRAJECTORY. INTENSITY GUIDANCE IS IN STRONG AGREEMENT ON THE OVERALL INTENSITY TREND AND TIMING BUT DIFFERS IN THE PEAK INTENSITY. ALL OF THE GUIDANCE PEAKS AT TAU 72, WITH A RANGE BETWEEN 60 KNOTS FOR THE HWRF, 75 KNOTS FOR THE HAFS-A, AND 85 KNOTS FOR THE COAMPS-TC (GFS). THE CTR1 RAPID INTENSIFICATION (RI) AID REACHES EVEN HIGHER, AT 95 KNOTS. THE CONSENSUS MEAN IS COMING IN AROUND 65-70 KNOTS, AND THE JTWC FORECAST IS SITUATED NEAR THE MEAN THROUGH THE FORECAST PERIOD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN