WDPN31 PGTW 040300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 29.6N 144.8E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 428 NM SOUTHEAST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTHWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 24 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT STORM, WHICH APPEARS TO BE MAKING A SLOW BUT STEADY COMEBACK. OVER THE COURSE OF THE PREVIOUS 12 HOURS, A SERIES OF MICROWAVE IMAGES REVEALED AN ASYMMETRIC STRUCTURE, WITH WEAK CONVECTION DISPLACED TO THE EAST OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). OVER THE PAST FEW HOURS, THE LLCC APPEARS TO BE SLOWING WORKING ITS WAY BACK UNDER THE CONVECTION AND ASSOCIATED MID-LEVEL VORTEX. THE LATEST MSI SUGGESTS THE MID-LEVEL VORTEX IS STRENGTHENING AND IF THE TWO CAN ALIGN, WE MAY SEE ANOTHER ROUND OF INTENSIFICATION. THERE HAS NOT BEEN A GOOD MICROWAVE PASS FOR MORE THAN SIX HOURS, THUS THE CONFIDENCE IN THE INITIAL POSITION IS LOW. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, CONSISTENT WITH THE PGTW CURRENT INTENSITY ESTIMATE OF T3.5, AND THE SATCON ESTIMATE OF 52 KNOTS. OVERALL, THE ENVIRONMENT APPEARS TO BE IMPROVING, WITH VERY LOW VWS, GOOD RADIAL OUTFLOW ALOFT, THOUGH THE OUTFLOW IS CURRENTLY CONFINED TO A SMALL REGION IN VICINITY OF THE STORM ITSELF, AND WARM SSTS. THERE REMAINS SOME LINGERING DRY AIR, PARTICULARLY ON THE WESTERN SIDE OF THE CIRCULATION, BUT THE INNER-CORE CONTINUES TO BE SUFFICIENTLY MOIST TO SUPPORT PERSISTENT CONVECTIVE ACTIVITY. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP LAYER SUBTROPICAL RIDGE (STR) COMPLEX EXTENDING FROM EAST OF THE SYSTEM SOUTHWESTWARD TO THE CENTRAL MARIANAS. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T2.5 - 35 KTS RCTP: T3.0 - 45 KTS KNES: T3.0 - 45 KTS CIMSS SATCON: 52 KTS AT 040000Z CIMSS ADT: 39 KTS AT 040000Z CIMSS AIDT: 42 KTS AT 040020Z CIMSS D-PRINT: 49 KTS AT 040000Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 0-5 KTS SST: 26-27 CELSIUS OUTFLOW: WEAK RADIAL OTHER FACTORS: LINGERING DRY MID-LEVEL AIR, PARTICULARLY TO THE WEST. ANALYSIS CONFIDENCE: INITIAL POSITION: LOW INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL STORM (TS) 04W (MUN) IS TRAVELING ALMOST DUE NORTH, ALONG THE WESTERN SIDE OF THE STEERING RIDGE. HOWEVER, THE NORTHERN EXTENSION OF THIS STEERING RIDGE IS RAPIDLY WEAKENING, IN FAVOR OF A BUILDING RIDGE OVER THE CENTRAL MARIANAS. OVER THE COURSE OF THE NEXT 12 HOURS, TS 04W WILL GRADUALLY TURN TOWARDS THE EAST-NORTHEAST, DRIVEN ALONG THE NORTHERN SIDE OF THE BUILDING RIDGE TO THE SOUTH. AFTER TAU 48, THE STR TO THE SOUTH MOVES WESTWARD WHILE A DEEP-LAYER BUBBLE HIGH DEVELOPS EAST OF TS 04W, DRIVING THE SYSTEM POLEWARD FROM TAU 48 TO TAU 96. AFTER TAU 96, THE SYSTEM WILL TRACK INTO A BREAK IN THE RIDGE AND BE CAUGHT UP IN THE MID-LATITUDE WESTERLIES AND QUICKLY TURN TO THE NORTHEAST. IN TERMS OF INTENSITY, AS SEEN IN THE MOST RECENT MSI AND IR LOOPS, THE VORTEX MAY BE TRYING TO REALIGN AT THE MOMENT. AS THIS PROCESS COMPLETES AND POLEWARD OUTFLOW IMPROVES, THERE SHOULD BE ENOUGH WARM WATER LEFT TO SUPPORT A SLOW BUT STEADY INTENSIFICATION OVER THE NEXT 36 HOURS. AROUND TAU 60, A STRONG MID-LATITUDE TROF AND DEFORMATION ZONE WILL MOVE IN FROM THE NORTHWEST, USHERING IN A SHARP INCREASE IN SHEAR AND DRY MID-LEVEL AIR, EFFECTIVELY DECAPITATING AND SMOTHERING TS 04W. THIS WILL MARK THE ONSET OF BOTH SUBTROPICAL TRANSITION (STT) AND A RAPID WEAKENING TREND, WHICH WILL CONTINUE THROUGH THE REMAINDER OF THE FORECAST PERIOD. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE SHOWS LITTLE CHANGE FROM THE PREVIOUS RUN. NAVGEM, GALWEM AND JGSM CONTINUE TO RACE THE SYSTEM TOWARDS THE NORTHEAST AFTER TAU 72, IN LINE WITH THEIR KNOWN BIASES. CONSIDERED AS UNREALISTIC, THESE MODELS HAVE BEEN DISCOUNTED. THE REMAINDER OF THE GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 48, WITH EVEN THE GFS AND GEFS MOVING INTO BETTER AGREEMENT WITH THE REST OF THE CONSENSUS. AFTER TAU 72, THE GFS BREAKS OFF FROM THE PACK HOWEVER, AND TRACKS FAR TO THE NORTHWEST BEFORE TURNING NORTH AT TAU 96, ALONG THE 144E LONGITUDE LINE. THE REMAINDER OF THE GUIDANCE PACKAGE TURNS NORTH-NORTHWESTWARD AFTER TAU 72 BEFORE TURNING NORTHEAST AFTER TAU 96. THE JTWC FORECAST IS POSITIONED CLOSE TO THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON THE OVERALL TREND LINE, WITH A RANGE OF PEAK INTENSITIES BETWEEN 60-75 KNOTS. THE JTWC FORECAST IS CONSISTENT WITH THE CONSENSUS MEAN THROUGH THE FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN