WDPN33 PGTW 090900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (CHAN-HOM) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 32.3N 150.7E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 668 NM SOUTHEAST OF MISAWA, JAPAN MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 03 KTS SIGNIFICANT WAVE HEIGHT: 18 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC), DEVOID OF SIGNIFICANT DEEP CONVECTION. TRACK MOTION HAS BECOME INCREASINGLY ERRATIC OVER THE PAST SIX HOURS DUE TO THE SYSTEM BEING CURRENTLY POSITIONED IN A WEAK AND COMPETING STEERING PATTERN DEFINED BY STRONG SUBTROPICAL RIDGING TO THE NORTHEAST AND SOUTHWEST, AND A COL WEAKNESS IN THE RIDGE TO THE NORTHWEST OVER HOKKAIDO. OVER THE LAST 1-2 HOURS, THE LLCC HAS BEGUN A COUNTERCLOCKWISE LOOP WHILE REMAINING QUASI- STATIONARY. ANIMATED WATER VAPOR IMAGERY, ATMOSPHERIC MOTION VECTORS (AMV), AND MODEL ANALYSIS FIELDS DEPICT A COMPLEX UPPER-LEVEL LOW (ULL) CENTERED JUST NORTH OF THE LLCC WITH A TROUGH EXTENDING TO THE SOUTHEAST. THE PROXIMITY OF THE ULL TO THE NORTH CREATES AN UNFAVORABLE ENVIRONMENT FOR TS 14W, INDUCING CONVERGENT NORTHWESTERLY SUBSIDENT FLOW AND SIGNIFICANT DRY AIR ENTRAINMENT OVER THE CORE. PHASE CLASSIFICATION WORKSHEETS INDICATE THE SYSTEM IS A HYBRID OR BORDERLINE SUBTROPICAL CYCLONE AT THIS TIME, EXHIBITING CHARACTERISTICS OF BOTH A TROPICAL AND SUBTROPICAL CYCLONE. UPSTREAM, JUST EAST OF JAPAN, WATER VAPOR IMAGERY DEPICTS A LARGE UPPER-LEVEL DEFORMATION ZONE AND A DEEP TROUGH MOVING RAPIDLY INTO THE NORTHERN SEA OF JAPAN (SOJ), BOTH OF WHICH WILL HAVE A SIGNIFICANT IMPACT ON THE FUTURE EVOLUTION OF TS 14W. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN THE MSI. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, BASED PRIMARILY ON THE CIMSS SATCON ESTIMATE AND PERSISTENCE WITH EARLIER SCATTEROMETER DATA. THE ENVIRONMENT IS MARGINALLY UNFAVORABLE WITH UNFAVORABLE UPPER-LEVEL CONDITIONS OFFSETTING OTHERWISE FAVORABLE PARAMETERS (WARM SEA SURFACE TEMPERATURES AND LOW VERTICAL WIND SHEAR). INITIAL WIND RADII BASIS: PERSISTENCE. CURRENT STEERING MECHANISM: COMPETING AND WEAK STEERING PATTERN, INCREASINGLY DOMINATED BY THE LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) CENTERED SOUTHWEST OF THE WESTERN ALEUTIANS. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS RCTP: T2.0 - 30 KTS CIMSS SATCON: 40 KTS AT 090440Z CIMSS ADT: 25 KTS AT 090600Z CIMSS AIDT: 27 KTS AT 090600Z CIMSS D-MINT: 33 KTS AT 090603Z CIMSS D-PRINT: 31 KTS AT 090640Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 10-15 KTS SST: 27-28 CELSIUS OUTFLOW: WEAK EASTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: GLOBAL MODELS AGREE THAT TS 14W WILL REMAIN TRAPPED IN A COMPETING STEERING PATTERN FOR ANOTHER FEW HOURS AND REMAIN QUASI-STATIONARY. BY TAU 12, HOWEVER, ALL MAJOR GLOBAL MODELS DEPICT A RAPID CHANGE IN THE UPPER-LEVEL PATTERN, WITH THE STR TO THE NORTHEAST BUILDING QUICKLY AND EXTENDING NORTHWESTWARD, SUPPLANTING THE RIDGE WEAKNESS CURRENTLY POSITIONED OVER HOKKAIDO. ONCE THIS OCCURS, TS 14W WILL EJECT FROM ITS QUASI-STATIONARY POSITION AND ACCELERATE NORTHWESTWARD. BY TAU 36, RIDGING OVER KOREA IS FORECAST TO RAPIDLY BUILD AND EXTEND NORTHEASTWARD, ULTIMATELY BRIDGING WITH THE RIDGE SOUTHEAST OF KAMCHATKA. THIS WILL DRIVE TS 14W WESTWARD AFTER TAU 48. LANDFALL ON THE EASTERN COAST OF HONSHU IS EXPECTED SHORTLY AFTER TAU 48, AS THE SYSTEM TRACKS QUICKLY WESTWARD ALONG THE SOUTHERN FLANK OF THE MID-LEVEL STR TO THE NORTH. THE SYSTEM EMERGES INTO THE SOJ BY TAU 60, BUT BEGINS TO DECELERATE AFTER TAU 72 AS IT SHALLOWS AND MOVES INTO A WEAKER STEERING PATTERN. IN TERMS OF INTENSITY, THE KEY FACTOR WILL BE THE PROXIMITY AND ORIENTATION TO A SERIES OF UPPER-LEVEL LOWS (ULL). THE CURRENT ULL IS POSITIONED IN AN UNFAVORABLE SUBSIDENT QUADRANT NORTH OF TS 14W. OVER THE NEXT 18-24 HOURS, THE ULL IS EXPECTED TO FILL AND MOVE SLIGHTLY NORTHWARD, WHICH WILL INHIBIT SIGNIFICANT INTENSIFICATION. AROUND TAU 24, THE DEEP TROUGH CURRENTLY CUTTING ACROSS THE NORTHERN SOJ WILL CUT OFF INTO AN ISOLATED ULL, WHICH WILL DIVE SOUTHWARD ALONG THE EASTERN COAST OF HONSHU TO A POSITION WEST OF TS 14W. THIS WILL OPEN UP A ROBUST POLEWARD OUTFLOW CHANNEL COINCIDENT WITH TS 14W CROSSING THE AXIS OF THE WARM KUROSHIO CURRENT. THESE TWO FACTORS COMBINE TO ALLOW FOR A PERIOD OF MARKED INTENSIFICATION, UP TO A PEAK OF 50-55 KNOTS BY TAU 36. HOWEVER, BY TAU 48, THE ULL WILL TRANSLATE SOUTH OF TS 14W, WHILE THE SYSTEM MOVES OVER THE COOLER WATERS OF THE OYASHIO CURRENT ALONG THE COAST. THESE NEGATIVE INFLUENCES WILL LEAD TO A GENERAL WEAKENING TREND AS THE SYSTEM APPROACHES LANDFALL. THE SYSTEM WILL RAPIDLY WEAKEN OVER LAND BEFORE EMERGING INTO THE SOJ AS A MINIMAL TROPICAL STORM, WHICH WILL BE IN THE EARLY PHASES OF SUBTROPICAL TRANSITION (STT). THE SYSTEM WILL COMPLETE STT BY TAU 72 WHILE SIMULTANEOUSLY WEAKENING DUE TO INCREASED VWS AND DRY AIR ENTRAINMENT THROUGH THE REMAINDER OF THE FORECAST PERIOD. MODEL DISCUSSION: TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT THROUGH THE FORECAST PERIOD. ALL CONSENSUS MEMBERS DEPICT A SLOW, QUASI-STATIONARY MOTION FOR THE FIRST FEW HOURS, FOLLOWED BY A SHARP TURN NORTHWESTWARD BEFORE TAU 12, THEN A WESTWARD TURN BY TAU 48. THE JGSM AND GFS DETERMINISTIC TRACKERS ARE POSITIONED ON THE NORTHERN EDGE OF THE GUIDANCE ENVELOPE, WHILE THE ECMWF AND EXPERIMENTAL GOOGLE DEEPMIND ARE POSITIONED ON THE SOUTHERN EDGE. CROSS-TRACK SPREAD INCREASES TO 100NM AT TAU 48, AND GRADUALLY INCREASES TO 150NM AT TAU 96. ENSEMBLE GUIDANCE IS CONTINUING TO TREND TOWARDS INCREASING UNCERTAINTY AND MEMBER DISPERSION. THE ENSEMBLE MEMBER ENVELOPE OF THE EXPERIMENTAL JTWC SUPER ENSEMBLE NOW STRETCHES FROM YOKOSUKA TO MISAWA AT LANDFALL, INCREASING TO A RANGE FROM SASEBO TO THE DPRK-ROK BORDER BY THE END OF THE FORECAST PERIOD. THE JTWC FORECAST IS POSITIONED CLOSE TO THE AI CONSENSUS MEAN, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT, WITH ALL CONSENSUS MEMBERS CONFINED TO A TIGHT ENVELOPE WHICH PEAKS BETWEEN 45-50 KNOTS AT TAU 36 FOLLOWED BY SHARP WEAKENING THROUGH THE REMAINDER OF THE FORECAST. THE JTWC FORECAST IS PLACED NEAR THE CONSENSUS MEAN WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN