WDPN31 PGTW 070900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YUN-YEUNG) WARNING NR 008// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 30.9N 137.0E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 297 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 12 KTS SIGNIFICANT WAVE HEIGHT: 20 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) UP TO THE 0600Z HOUR DEPICTED A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC), WITH FLARING DEEP CONVECTION SHEARED TO THE NORTH. SUBSEQUENT IMAGERY SHOWS THE LLCC HAS TUCKED UP UNDER THE CONVECTION. THE ASSESSED CENTER NOW LIES UNDER THE DEVELOPING CENTRAL DENSE OVERCAST, LIKELY IN THE AREA OF OVERSHOOTING TOPS AND A BURST OF INTENSE LIGHTING ACTIVITY. HOWEVER, THE CONVECTION REMAINS DISORGANIZED AT PRESENT, BUT SINCE THE LLCC LIES ON THE VERY EXTREME EDGE OF JAPANESE RADAR COVERAGE AND THE LACK OF RECENT MICROWAVE IMAGERY, WE HAVE NO WAY OF KNOWING IF THEY SYSTEM IS BECOMING BETTER ORGANIZED AT THE MOMENT. THE LAST MICROWAVE IMAGE, A 070430Z AMSR2 PASS, REVEALED TIGHTLY CURVED, SHALLOW BANDING WRAPPING INTO A DEFINED LLCC, WITH THE BULK OF THE CONVECTION CONFINED TO A LINEAR BAND EXTENDING FROM NORTH TO SOUTHEAST OF THE CENTER. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC DELINEATED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, HEDGED SLIGHTLY HIGHER THAN THE BULK OF THE AGENCY ESTIMATES, CONSISTENT WITH EARLIER SCATTEROMETER DATA AND THE CIMSS AIDT AND SATCON ESTIMATES. THE REMNANTS OF 11W (KIROGI) ARE STILL LURKING ABOUT 200NM SOUTHWEST OF 12W'S INITIAL POSITION, RAPIDLY MOVING EAST-SOUTHEASTWARD, AND UNDERGOING BINARY INTERACTION WITH 12W. THE REMNANTS OF 11W WILL CONTINUE TO TRACK A CYCLONIC TRAJECTORY, MOVING STEADILY CLOSER TO 12W, AND ARE EXPECTED TO MERGE INTO 12W AND ULTIMATELY DISSIPATE AS A DISCRETE CIRCULATION, WITHIN THE NEXT 12 HOURS. INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER ASCAT DATA. CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE EAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS RCTP: T2.0 - 30 KTS KNES: T3.0 - 45 KTS CIMSS SATCON: 39 KTS AT 070430Z CIMSS ADT: 34 KTS AT 070530Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 30-35 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: DRY AIR TO THE WEST, WHICH IS BEING ENTRAINED INTO THE SOUTHERN PORTION OF THE CIRCULATION. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: WHILE THE OVERALL PHILOSOPHY HAS NOT CHANGED, THE TRACK OF 12W HAS SHIFTED SIGNIFICANTLY WESTWARD WITH THIS FORECAST, NOW TAKING THE TRACK NORTHWARD, CROSSING HONSHU AND EMERGING INTO THE SEA OF JAPAN. FORECAST DISCUSSION: TS 12W CONTINUES TO TRACK NORTH-NORTHEASTWARD ALONG THE WESTERN SIDE OF THE STEERING RIDGE TO THE EAST. HOWEVER, THE MOST RECENT ANIMATED MSI SUGGESTS IT MAY BE STARTING TO SLOW DOWN A BIT, LIKELY IN RESPONSE TO THE BINARY INTERACTION WITH THE REMNANTS OF 11W, WHICH AS THEY PASS TO THE SOUTH, WILL SERVE TO GENTLY TUG 12W FROM THE SOUTH. THE TRACK IS ALSO EXPECTED TO SHIFT A BIT TO THE WEST AS THE REMNANTS OF 11W MERGE WITH 12W WHILE AT THE SAME TIME THE RIDGE TO THE EAST BUILDS AND REORIENTS TO A MORE NORTH-SOUTH AXIS. THE NET EFFECT OF THESE SMALL SHIFTS IN STEERING IS THAT THE LANDFALL POSITION IS SHIFTED WEST TO THE VICINITY OF HAMAMATSU, AND NOW EXPECTED JUST PRIOR TO TAU 24. THE SYSTEM IS UNDER AN AREA OF SIGNIFICANT SHEAR, APPROACHING 40 KNOTS IN THE LATEST CIMSS ANALYSIS. HOWEVER, THE FLOW IS HIGHLY DIFFLUENT AND DIVERGENT, WHICH IS ALLOWING THE RECENT BURST OF CONVECTIVE ACTIVITY TO DEVELOP NEAR THE LLCC. THIS SETUP IS NOT EXPECTED TO LAST ALL THAT LONG HOWEVER, AND THE VORTEX IS UNLIKELY TO ALIGN VERTICALLY IN THE FACE OF THE STRONG SHEAR AND SIGNIFICANT DRY AIR ENTRAINMENT THAT IS JUST STARTING TO IMPACT THE SYSTEM. THE STRONG DIFFLUENCE AND DIVERGENCE ALOFT IS FORECAST TO REMAIN IN PLACE TO THE NORTH OF 12W FOR THE NEXT 12 HOURS OR SO, WHICH WILL SUPPORT A SLIGHT UPTICK TO A 45 KNOT PEAK INTENSITY BY TAU 12. THEREAFTER, SHEAR WILL COMPLETELY OVERTAKE THE SYSTEM AS IT IS ENGULFED BY DRY AIR AND MOVES OVER THE COMPLEX TERRAIN OF HONSHU, LEADING TO A RAPID WEAKENING AFTER TAU 24. BY TAU 36, WHAT REMAINS OF 12W IS EXPECTED TO MOVE INTO THE SEA OF JAPAN ALONG THE NORTH-SOUTH ORIENTED LOW TO MID-LEVEL RIDGE SET UP TO THE EAST OF JAPAN. BY TAU 48, THE REMNANTS OF 12W WILL TURN TOWARDS THE NORTHEAST AS IT ROUNDS THE RIDGE AXIS, BUT WILL FULLY DISSIPATE NO LATER THAN 72, AND POTENTIALLY AS EARLY AS TAU 48. DUE TO THE COMPLEX TERRAIN OF CENTRAL HONSHU, THERE IS A HIGH PROBABILITY THAT A SECONDARY AREA OF LOW PRESSURE AND LLCC WILL SPLIT OFF FROM THE PRIMARY LLCC, AND RIDE UP THE EAST SIDE OF THE JAPANESE ALPS WHILE THE PRIMARY CIRCULATION ASSOCIATED WITH 12W TRACKS NORTH INTO THE SEA OF JAPAN. IF THE SECONDARY CIRCULATION DOES DEVELOP, IT IS EXPECTED TO BE VERY WEAK. JTWC WILL CLOSELY MONITOR THE SITUATION TO ASCERTAIN WHEN AND IF THE SECONDARY CIRCULATION DEVELOPS. MODEL DISCUSSION: DETERMINISTIC AND PROBABILISTIC MODEL GUIDANCE HAS SHIFTED SIGNIFICANTLY WEST WITH THIS MODEL RUN. IN FACT, ALL MEMBERS OF THE CONSENSUS HAVE SHIFTED OVER TO A TRACK THAT IS CONSISTENT WITH THE JTWC FORECAST, INCLUDING THE NAVGEM WHICH HAS SHIFTED FROM BEING AN OUTLIER ON THE EAST SIDE OF THE TRACK ENVELOPE, TO NOW BEING THE WESTERN OUTLIER, TAKING THE SYSTEM NEAR KYOTO BEFORE MOVING INTO THE SEA OF JAPAN. THE EASTERN EDGE OF THE ENVELOPE IS NOW MARKED BY THE ECMWF ENSEMBLE MEAN, AND THE REMAINDER OF THE GUIDANCE CONSTRAINED BETWEEN THE TWO. CROSS-TRACK SPREAD IS 125NM AT TAU 36, AND 150NM AT TAU 72. ALONG-TRACK SPREAD INCREASES DRAMATICALLY AFTER TAU 48 AS WELL. THE JTWC TRACK LIES ON THE EASTERN SIDE OF THE GUIDANCE ENVELOPE, AND THIS MARKS A MAJOR SHIFT IN THE FORECAST TRACK. CONFIDENCE IS MEDIUM, ENHANCED BY THE FACT THAT ALL CONSENSUS GUIDANCE, AS WELL AS THE GEFS, MOGREPS AND ECENS ENSEMBLE MEANS HAVE ALSO COME OVER TO THE MORE NORTHWARD TRACK. INTENSITY GUIDANCE REMAINS IN GOOD AGREEMENT, WITH ALL GUIDANCE SUGGESTING A BRIEF BUMP TO 45-50 KNOTS PRIOR TO LANDFALL FOLLOWED BY RAPID WEAKENING AND FULL DISSIPATION NO LATER THAN TAU 72. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: LOW// NNNN