WDXS31 PGTW 131500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 17S (ZELIA) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.3S 118.2E INITIAL INTENSITY: 130 KTS GEOGRAPHIC REFERENCE: 64 NM NORTH-NORTHWEST OF PORT HEDLAND, AUSTRALIA MOVEMENT PAST 6 HOURS: SOUTHWARD AT 02 KTS SIGNIFICANT WAVE HEIGHT: 52 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL CYCLONE (TC) 17S (ZELIA) REMAINS QUITE FORMIDABLE, WITH THE LATEST ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWING RAPID REDEVELOPMENT OF A PINHOLE EYE FEATURE, MEASURING JUST 7NM ACROSS. A SERIES OF MICROWAVE IMAGES OVER THE PAST SIX HOURS SUGGESTS THAT TC 17S DID NOT COMPLETE THE EYEWALL REPLACEMENT CYCLE (ERC) THAT BEGAN EARLIER IN THE DAY. A 131036Z WSF-M 89GHZ IMAGE DEPICTS AN ASYMMETRIC INNER-CORE STRUCTURE, WITH A VERY THIN EYEWALL ALONG THE SOUTHEASTERN SIDE OF THE EYE, WHILE THE EYEWALL IS MUCH MORE IMPRESSIVE ACROSS THE NORTHERN HEMISPHERE OF THE CIRCULATION. THIS MAY BE DUE TO SOME DRY AIR AND SUBSIDENCE, AS DEPICTED IN BOTH THE HAFS-A AND HWRF MODEL CROSS-SECTIONS. WHILE THE PINHOLE EYE HAS RECENTLY REEMERGED, CLOUD-TOP TEMPERATURES HAVE CONTINUE TO INCREASE AS WELL, NOW ALMOST 10C WARMER THAN 12 HOURS AGO. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PINHOLE EYE IN THE EIR, AS WELL AS RADAR FIXES FROM PGTW BASED ON ABOM RADAR DATA. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON THE MAJORITY OF THE AGENCY FIXES AT T6.5 (127 KNOTS), SUPPORTED BY THE AIDT, DMINT AND DPRINT ESTIMATES FROM CIMSS. THE ENVIRONMENT REMAINS FAVORABLE, WITH ZESTY SSTS OF 32C RIGHT ALONG THE COAST, HIGH OHC, VERY STRONG DUAL-CHANNEL OUTFLOW AND LOW DEEP-LAYER WIND SHEAR. THE ONLY POSSIBLE NEGATIVE INFLUENCES ARE THE HIGHER SHEAR AT THE OUTFLOW LAYER AND THE DRY AIR IN THE LOW- TO MID-LEVELS TO THE SOUTH OF THE CORE OF THE SYSTEM. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: WEAK STEERING PATTERN. THE SYSTEM IS WITHIN A LARGE COL REGION, WITH RIDGES TO THE WEST OVER OPEN WATERS AND TO THE EAST OVER NORTHERN AUSTRALIA, AND TROUGHING OR LOW HEIGHT CENTERS OVER THE JAVA SEA AND THE GREAT AUSTRALIAN BIGHT. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.5 - 127 KTS KNES: T7.0 - 140 KTS DEMS: T6.5 - 127 KTS APRF: T6.5 - 127 KTS CIMSS ADT: 129 KTS AT 131130Z CIMSS AIDT: 122 KTS AT 1311200Z CIMSS D-MINT: 129 KTS AT 131036Z CIMSS D-PRINT: 129 KTS AT 131200Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD OTHER FACTORS: MODERATE TO HIGH SOUTHEASTERLY SHEAR AT THE OUTFLOW LAYER (200-400MB). 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: TC 17S IS STILL DRIFTING SLOWLY AND AIMLESSLY, LINGERING JUST OFFSHORE TO THE NORTH OF PORT HEDLAND. THE MOST RECENT ANIMATED EIR SUGGESTS THE SYSTEM IS PERFORMING ANOTHER PIROUETTE OR SMALL LOOP, AS IT REMAINS WITHIN THE LARGE COL REGION WITH LITTLE TO NO MAJOR STEERING INFLUENCE. THE RIDGING OVER NORTHER AUSTRALIA IS EXPECTED TO BUILD OVER THE NEXT DAY, WHILE THE STR TO THE WEST MOVES FURTHER WEST, ALLOWING THE SYSTEM TO COME MORE UNDER THE STEERING INFLUENCE OF THE STR TO THE EAST. HOWEVER, THAT PROCESS WILL NOT FULLY EXERT ITSELF UNTIL AFTER LANDFALL AND THUS, TC 17S IS EXPECTED TO SLOWLY DRIFT SOUTHWARD UNTIL IT MAKES LANDFALL, AROUND TAU 24. THE EXACT TIME OF LANDFALL IS HIGHLY UNCERTAIN DUE TO THE WEAK STEERING INFLUENCES, AND SIGNIFICANT SHIFTS IN THE TIMING OF LANDFALL ARE POSSIBLE. THE CURRENT FORECAST ANTICIPATE THE SYSTEM MOVING INLAND JUST WEST OF PORT HEDLAND WITHIN THE NEXT 24 HOURS, THEN ACCELERATING TOWARDS THE SOUTH ALONG THE WEST SIDE OF THE BUILDING STR TO THE EAST. THE INNER-CORE OF TC 17S IS EXTREMELY SMALL, AND THUS SUBJECT TO RAPID FLUCTUATIONS IN INTENSITY, WHICH ARE HIGHLY LIKELY IN THE NEAR-TERM, AS MICROSCALE INNER-CORE FACTORS WILL NOW BE THE PRIMARY DRIVER OF THE INTENSITY FROM THIS POINT FORWARD. ADDITIONALLY, THE LONGER THE SYSTEM CONTINUES TO LOLLYGAG OFF THE COAST THE MORE THAT UPWELLING WILL PLAY A NEGATIVE ROLE. THE FORECAST CALLS FOR INTENSIFICATION TO 140 KNOTS BY TAU 12, AND IT IS POSSIBLE THAT ADDITIONAL INTENSIFICATION UP TO THE POINT OF LANDFALL MAY OCCUR. ONCE ASHORE, THE SYSTEM WILL RAPIDLY WEAKEN AND FULLY DISSIPATE WITHIN 72 HOURS. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE HAS SHIFTED ABOUT 30NM TO THE EAST WITH THE MOST RECENT RUN AND THE ENTIRE GUIDANCE ENVELOPE LIES EAST OF THE PREVIOUS FORECAST TRACK. THE ONLY MEMBERS TAKING THE SYSTEM INLAND NEAR THE PREVIOUS FORECAST POINT ARE THE HWRF AND HAFS-A, WHICH ARE NOT MEMBERS OF THE TRACK CONSENSUS. ALL OF THE CONSENSUS MEMBERS, WITH THE EXCEPTION OF NAVGEM, ARE TIGHTLY PACKED AROUND A LANDFALL POINT JUST WEST OF PORT HEDLAND. AFTER LANDFALL, THE TRACK CONSENSUS MODELS BEGIN TO SPREAD OUT, TO ABOUT 250NM BY THE END OF THE FORECAST. THE JTWC TRACK LIES CLOSE TO THE CONSENSUS MEAN THROUGH THE FORECAST. HOWEVER, DUE TO THE UNCERTAINTIES ASSOCIATED WITH THE WEAK STEERING PATTERN, CONFIDENCE IS LOW EVEN IN THE EARLY PORTION OF THE FORECAST. INTENSITY GUIDANCE IS MIXED. THE BULK OF THE GUIDANCE SUGGESTS THE SYSTEM WILL NOT INTENSIFY FURTHER BUT WILL MAINTAIN ITS CURRENT INTENSITY THROUGH LANDFALL BEFORE RAPIDLY WEAKENING AFTER TAU 24. HOWEVER, THE HAFS-A IN PARTICULAR AND TO A LESSER EXTENT THE HWRF, SHOW THE SYSTEM INTENSIFYING SIGNIFICANTLY BEFORE LANDFALL. THE NON-INTERPOLATED 0600Z HAFS-A RUN IN FACT SHOWS A PEAK INTENSITY OF 160 KNOTS AT TAU 12 WHILE THE INTERPOLATED RUN SHOWS A PEAK OF 140 KNOTS. WHILE 160 KNOTS MAY BE A BIT UNREALISTIC, IT IS NOT IMPOSSIBLE CONSIDERING THE ENVIRONMENTAL CONDITIONS. THE JTWC FORECAST BASICALLY FOLLOWS THE INTERPOLATED HAFS-A RUN THROUGH TAU 24, THEN FOLLOWS THE CONSENSUS THROUGH THE REMAINDER OF THE FORECAST PERIOD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: LOW INTENSITY 0 - 72 HR: MEDIUM// NNNN