WDPN31 PGTW 242100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (SURIGAE) WARNING NR 007// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.3N 131.7E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 483 NM SOUTH-SOUTHEAST OF KADENA AB MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 16 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL STORM (TS) 25W (SURIGAE) WITH A SLIGHTLY ELONGATED AND ALMOST ENTIRELY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) ON THE SOUTHEASTERN PERIPHERY OF A PERSISTENT AREA OF CONVECTION. A 241625 AMSR3 89 GHZ MICROWAVE IMAGE SUPPORTS THE ELONGATED AND SHEARED NATURE OF 25W, SHOWING IT DEVOID OF ANY CONVECTIVE BANDING OUTSIDE OF THE MASS OF CONVECTION TO THE NORTHWEST. VERTICAL WIND SHEAR IS EVIDENT IN EIR, ALSO SHOWING THAT CONVECTION REMAINS CONFINED TO THE NORTHWEST OF THE LLCC DUE TO 10-15 KTS OF VERTICAL WIND SHEAR (VWS), ADDITIONALLY INTRODUCING DRY AIR INTO THE SYSTEM AS IT HAS BECOME DECOUPLED FROM THE UPPER-LEVEL CONVECTION. THE REMAINDER OF ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE WITH WARM (29-30 C) SEA SURFACE TEMPERATURES (SSTS) AND MODERATE OUTFLOW ALOFT. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC AND MICROWAVE IMAGE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE SLIGHTLY LARGER SPREAD BETWEEN AGENCY DVORAK FIXES AND OBJECTIVE ESTIMATES LISTED BELOW. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE CENTERED TO THE NORTH-NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T2.5 - 35 KTS RCTP: T2.5 - 35 KTS CIMSS SATCON: 43 KTS AT 241647Z CIMSS ADT: 47 KTS AT 241740Z CIMSS AIDT: 38 KTS AT 241740Z CIMSS D-MINT: 33 KTS AT 241648Z CIMSS D-PRINT: 31 KTS AT 241740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: VORTEX DECOUPLING AND DRY AIR ENTRAINMENT ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 25W HAS TAKEN A SLIGHTLY MORE NORTHWESTWARD JOG OVER THE LAST SIX HOURS THAN PREVIOUSLY FORECAST, BUT IS FORECAST TO CONTINUE A GENERAL WEST-NORTHWESTWARD TRACK AT A STEADY RATE FOR THE NEXT 24 HOURS. AFTER TAU 24, 25W IS FORECAST TO SLOW IN TRACK SPEED AND TURN POLEWARD AS IT APPROACHES A WEAKNESS IN THE RIDGING BETWEEN THE PRIMARY STEERING SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTH-NORTHEAST AND ANOTHER STR CENTERED OVER SOUTHERN CHINA. 25W IS EXPECTED TO MOVE SLOWLY POLEWARD UNTIL AROUND TAU 72 AT WHICH POINT IT IS FORECAST TO TURN NORTHEASTWARD AND RECURVE THE STR TO THE EAST. THERE REMAINS UNCERTAINTY IN THE RESULTANT TRACK AND TRACK SPEED IN THIS OUTCOME AS GLOBAL MODEL FIELDS DEPICT VARYING STEERING ENVIRONMENTS DURING THIS TIME OF RECURVATURE BETWEEN TAUS 48 AND 96, BOTH IN REGARDS TO THE DISPOSITION OF THE TWO STRS, AS WELL AS THE POSSIBLE IMPACTS OF A MID-LATITUDE SHORTWAVE TROUGH PROPAGATING EASTWARD. THE GFS MODEL FIELD DEPICTS THE STR TO THE EAST RECEDING AS WELL AS THE MID-LAT TROUGH WITHOUT ENOUGH SUPPORT TO PULL 25W POLEWARD AND INSTEAD DEPICTS THE SYSTEM SLOWING IN TRACK SPEED AND STALLING JUST SOUTH OF THE RYUKYU ISLANDS FOR THE REMAINDER OF THE FORECAST PERIOD. ALTERNATIVELY, THE ECMWF AND AI MODEL FIELDS ASSESS THE TROUGH TO HAVE MORE DYNAMIC SUPPORT TO BRING 25W POLEWARD AROUND TAU 72 IN CONJUNCTION WITH THE EASTERN STR MAINTAINING STRONGER STEERING INFLUENCE FOR THE ENTIRETY OF THE FORECAST PERIOD, AND IS ULTIMATELY WHAT IS DEPICTED IN THE OFFICIAL JTWC FORECAST TRACK. REGARDING INTENSITY, 25W IS FORECAST TO GRADUALLY INTENSIFY OVER THE NEXT 24 HOURS AS IT AXISYMMETRIZES, VWS ABATES, AND IT IMPROVES IN VERTICAL STRUCTURE. FROM TAU 24 TO 48 A PERIOD OF RAPID INTENSIFICATION (RI) IS FORECAST AS 25W NEARS THE AXIS OF RIDGING AND SUBSEQUENT ENHANCED OUTFLOW. A PEAK OF AROUND 95 KTS IS EXPECTED TO OCCUR BETWEEN TAUS 60 AND 72 AFTER THIS RI BEFORE A STEADY WEAKENING PHASE BEGINS DUE TO INCREASED VWS AND SUBSEQUENT DRY AIR ENTRAINMENT. THERE IS ALSO UNCERTAINTY WITH THE INTENSITY FORECAST DUE TO IT BEING HIGHLY DEPENDENT ON THE ULTIMATE TRACK OF 25W. THE ALTERNATE SCENARIO DEPICTED BY GFS COULD RESULT IN A HIGHER PEAK INTENSITY IF 25W REMAINS IN AN AREA OF MORE FAVORABLE CONDITIONS. MODEL DISCUSSION: TRACK MODEL GUIDANCE REMAINS DIVIDED INTO THREE MAIN GROUPINGS OF A STRAIGHT NORTHWESTWARD TRACK FOR THE REMAINDER OF THE FORECAST PERIOD AND TWO RECURVING SCENARIOS WITH THE REMAINDER OF PHYSICS-BASED MODELS BEING MARKEDELY SLOWER THAN THE FINAL GROUP WHICH IS MADE UP OF THE AI GUIDANCE AND DEPICTS THE QUICKEST RECURVATURE AND NORTHEASTWARD TRACK. THIS HAS RESULTED IN A TOTAL ALONG TRACK SPREAD OF 700 NM BY TAU 120 BETWEEN THESE THREE GROUPS. AS DISCUSSED ABOVE, THE OFFICIAL JTWC FORECAST TRACK IS LAID IN AGREEMENT WITH THE STEERING SCENARIO DEPICTED BY ECMWF AND AI GUIDANCE IN A RECURVATURE SCENARIO, CLOSELY IN LINE WITH THE MULTI-MODEL AND AI CONSENSUS TRACK FOR THE ENTIRETY OF THE FORECAST PERIOD AND IN LINE WITH THE MULTI- MODEL CONSENSUS TRACK SPEED OUT TO TAU 72, THEN BLENDING THE TRACK SPEEDS OF THE MULTI-MODEL AND AI CONSENSUS FROM TAU 72 TO 120 AS THEY BEGIN TO DIVERGE, WITH OVERALL LOW CONFIDENCE DUE TO THE LARGE SPREAD IN GUIDANCE. MODEL INTENSITY GUIDANCE ALSO REMAINS SPLIT AS THE MOST RELIABLE INTENSITY AIDS DEPICT VERY DIFFERENT TRACK OUTCOMES WITH COAMPS-TC AND HAFS-A STALLING 25W SOUTH OF THE RYUKYU ISLANDS AND THUS DEPICTING 25W REACHING NEAR SUPERTYPHOON INTENSITIES, WHEREAS THE GOOGLE DEEPMIND DEPICTS AN EARLIER AND LOWER PEAK OF 80 KTS AS IT TRACKS THE SYSTEM MUCH MORE QUICKLY THROUGH THE RECURVATURE. HOWEVER, BOTH AI AND MESOSCALE ENSEMBLE INTENSITY GUIDANCE CONTINUE TO SHOW SUPPORT FOR RI TO OCCUR BETWEEN TAUS 24 TO 60, LENDING SOME CONFIDENCE TO THAT PORTION OF THE FORECAST. ALL GUIDANCE IS IN GOOD AGREEMENT ON A SHORT TERM STEADY INTENSIFICATION PRIOR TO THE POSSIBLE RI, AS WELL AS AGREEMENT ON A GENERAL WEAKENING TREND AFTER TAU 72, HOWEVER THE HIGHEST UNCERTAINTY REMAINS WITH THE TIMING AND MAGNITUDE OF PEAK INTENSITY. AS SUCH, THE OFFICIAL JTWC INTENSITY FORECAST IS ASSESSED WITH LOW CONFIDENCE THROUGHOUT THE FORECAST PERIOD, IN GOOD AGREEMENT WITH THE MULTI-MODEL CONSENSUS OUT TO TAU 48 AND THEN ABOVE IT TO BETTER CAPTURE THE EXPECTED RI PERIOD, COMING BACK INTO AGREEMENT WITH THE CONSENSUS BY TAU 96. FORECAST CONFIDENCE: TRACK 00-72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 00-72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN