WDPN31 PGTW 030300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (DOLPHIN) WARNING NR 029// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 24.4N 148.4E INITIAL INTENSITY: 100 KTS GEOGRAPHIC REFERENCE: 388 NM EAST OF IWO TO MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 52 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY) 12W UNDERGOING SIGNIFICANT STRUCTURAL CHANGES. THE EYE HAS BECOME MORE CLOUD-FILLED AND IS COOLING, WHILE THE SURROUNDING CLOUD TOPS OF THE CENTRAL DENSE OVERCAST (CDO) HAVE WARMED. MEANWHILE, MULTIPLE, VIGOROUS BANDS SPIRAL AROUND THE CDO. THE DETERIORATION IS THE RESULT OF THE ANTICIPATED EYEWALL REPLACEMENT CYCLE (ERC). A 021831Z SSMIS 37 GHZ IMAGE CONFIRMS THAT THE ERC HAS BEGUN IN EARNEST, CLEARLY SHOWING A LOWER-LEVEL RING COMPLETELY SURROUNDING THE INNER EYEWALL. A 022327Z ASCAT-C PASS REVEALS THAT THE STORM-FORCE WIND RADII HAVE CONTRACTED SLIGHTLY, WHILE THE GALE-FORCE EXTENT HAS EXPANDED. THE WIND FIELD IS ALSO QUITE ASYMMETRIC, WITH MUCH LARGER WIND RADII OBSERVED IN THE NORTHERN SEMICIRCLE. THE SURROUNDING ENVIRONMENT REMAINS FAVORABLE, CHARACTERIZED BY VERY WARM SEA SURFACE TEMPERATURES (SST) AND LOW VERTICAL WIND SHEAR (VWS), OFFSET BY LOWER OCEAN HEAT CONTENT (OHC). THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE IN THE MSI. DUE TO THE CONTINUED DEGRADATION OF THE INNER CORE, THE INITIAL INTENSITY HAS BEEN LOWERED TO 100 KTS, WHICH IS SUPPORTED BY THE MAJORITY OF T5.5 AGENCY DVORAK FIXES. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: THE SOUTHWESTWARD EXTENSION OF THE DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED FAR TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T5.5 - 102 KTS RJTD: T5.5 - 102 KTS RCTP: T5.0 - 90 KTS KNES: T5.5 - 102 KTS CIMSS SATCON: 113 KTS AT 021500Z CIMSS ADT: 102 KTS AT 030000Z CIMSS AIDT: 100 KTS AT 030000Z CIMSS D-MINT: 108 KTS AT 021918Z CIMSS D-PRINT: 104 KTS AT 030000Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 30-31 CELSIUS OUTFLOW: MODERATE RADIAL 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: TY 12W WILL MAINTAIN A WEST-NORTHWESTWARD TRAJECTORY, STEERED ALONG THE SOUTHWESTERN PERIPHERY OF A STR CENTERED NEAR 42N 176W. BY TAU 36, A SEPARATE RIDGE OVER THE KOREAN PENINSULA WILL CAPTURE THE SYSTEM AND DRIVE IT IN A SIMILAR DIRECTION OF MOTION. AS THE SYSTEM TRACKS TOWARD THE RYUKYU ISLANDS, A TROUGH PASSING THROUGH EASTERN SIBERIA WILL FLATTEN THE STEERING RIDGE, RESULTING IN A WEAKER STEERING GRADIENT. CONSEQUENTLY, THE FORWARD MOTION OF TY 12W WILL SLOW FROM 12 KTS AT TAU 36 TO 08 KTS BY TAU 120. THE COMBINATION OF LOWER OHC AND THE ERC HAS SIGNIFICANTLY WEAKENED THE SYSTEM BY 25 KTS OVER THE PAST 24 HOURS. CONTINUED WEAKENING TO AROUND 85 KTS WILL OCCUR DUE TO THE ONGOING ERC. AN ADDITIONAL COMPLICATING FACTOR WILL EMERGE BETWEEN TAU 12 AND TAU 36, AS THE SYSTEM ENCOUNTERS A BRIEF PERIOD OF LOW TO MODERATE NORTHERLY VWS OF 15-20 KT, INDUCED BY AN UPPER-LEVEL RIDGE OVER THE SEA OF JAPAN. IT IS POSSIBLE THAT THIS SHEAR COULD DISRUPT AND PROLONG THE ERC, POTENTIALLY CAUSING MORE WEAKENING THAN CURRENTLY FORECAST. BEYOND TAU 36, TY 12W WILL TRAVERSE VERY WARM SST OF 30-31 DEGREES CELSIUS IN A LOWER-SHEAR ENVIRONMENT. HOWEVER, THE PERSISTENTLY LOW OHC ALONG THE FORECAST TRACK WILL LIMIT INTENSIFICATION. THEREFORE, THE FORECAST CALLS FOR THE INTENSITY OF TY 12W TO REMAIN GENERALLY STEADY-STATE THROUGH TAU 120. THE ONGOING ERC WILL CAUSE THE WIND FIELD TO FURTHER EXPAND, ENSURING THAT HAZARDS WILL EXTEND FAR FROM THE STORM CENTER. MODEL DISCUSSION: THE MODEL TRACKERS ARE TIGHTLY GROUPED THROUGH THE ENTIRE FORECAST PERIOD, ALL DEPICTING A WEST-NORTHWESTWARD MOTION. THE SIGNIFICANT FORECAST CHALLENGE LIES IN THE STORM'S FORWARD SPEED IN THE EXTENDED PERIOD. THE ALONG-TRACK SPREAD INCREASES SIGNIFICANTLY FROM 170 NM AT TAU 96 TO 260 NM BY TAU 120. THIS DIVERGENCE IN TIMING ARISES FROM MODEL SOLUTIONS THAT DIFFER IN HOW THE RIDGE OVER THE KOREAN PENINSULA EVOLVES. THE FASTER MODELS, WHICH INCLUDE ECMWF AND NAVGEM, KEEP A STRONGER RIDGE IN PLACE, WHILE THE SLOWER SOLUTIONS OF GFS AND THE EXPERIMENTAL GOOGLE DEEPMIND ERODE THE RIDGE TO A GREATER EXTENT. THE JTWC FORECAST TRACK IS SET WITH HIGH CONFIDENCE NEAR THE MULTI-MODEL CONSENSUS. AT TAU 96 AND TAU 120, THE FORECAST POINTS LIE NEARLY HALFWAY BETWEEN THE FASTER ECMWF AND THE SLOWER GFS SOLUTIONS. SIGNIFICANT SPREAD EXISTS AMONG THE INTENSITY AIDS. COAMPS-TC, THE LONE OUTLIER THAT INTENSIFIES TY 12W TO 130 KTS, IS DISCOUNTED. THE JTWC INTENSITY FORECAST IS MOST CLOSELY ALIGNED WITH THE HAFS-A MODEL THROUGH TAU 36, SHOWING STEADY WEAKENING TO ACCOUNT FOR THE ONGOING ERC AND A TEMPORARY INCREASE IN VWS. THEREAFTER, THE FORECAST TRENDS CLOSER TO THE DEEPMIND SOLUTION. HAFS-A NOTABLY PREDICTS SIGNIFICANT RE-INTENSIFICATION BEGINNING AT TAU 96, WITH THE SYSTEM REACHING OVER 100 KTS BY TAU 120. THIS SOLUTION SUGGESTS THE POTENTIAL FOR THE VERY LARGE EYEWALL TO ERODE AND A NEW, SMALLER INNER CORE TO QUICKLY CONSOLIDATE. FOR NOW, THE FORECAST KEEPS THE INTENSITY UNCHANGED IN THE EXTENDED PERIOD. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: HIGH INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN