WDXS31 PGTW 130900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 17S (ZELIA) WARNING NR 009// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.1S 118.2E INITIAL INTENSITY: 125 KTS GEOGRAPHIC REFERENCE: 75 NM NORTH-NORTHWEST OF PORT HEDLAND, AUSTRALIA MOVEMENT PAST 6 HOURS: SOUTHWARD AT 01 KTS SIGNIFICANT WAVE HEIGHT: 45 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE EYE IS NOW CLOUD-FILLED, WITH EYE TEMPERATURES NOW APPROXIMATING THE CLOUD-TOP TEMPERATURES, WHICH ARE THEMSELVES WARMING. A 130527Z AMSR2 89GHZ MICROWAVE IMAGE REVEALS A SIGNIFICANT EROSION OF THE CORE CONVECTION AND EYEWALL ON THE SOUTHEASTERN SIDE OF THE EYE. THIS IS CONSISTENT WITH THE MODEL-DERIVED SOUNDINGS INDICATING STRONG (20-30 KNOT) SOUTHEASTERLY SHEAR, CONFIRMED BY THE LATEST BROOME SOUNDING, WHICH ALSO SHOWS STRONG SOUTHEASTERLIES ABOVE 250MB. THE LOWER-LEVEL STRUCTURE REMAINS STRONG AND THE STRONG WINDS DO NOT EXTEND DOWN BELOW 400MB, SO THE BULK OF THE VORTEX REMAINS VERTICALLY ALIGNED. THE LATEST CIMSS M-PERC EYEWALL REPLACEMENT CYCLE (ERC) TOOL SHOWED A 96 PERCENT PROBABILITY OF AND ERC, AND ANIMATED RADAR DATA FROM ABOM SUGGESTS AN ERC IS IN FACT OCCURRING AS OF THE 0600Z HOUR, WITH A SMALL INNER-CORE SURROUNDED BY A STRENGTHENING SECONDARY EYEWALL. THIS, COMBINED WITH LIKLEY UPWELLING DUE TO THE QUASI-STATIONARY MOVEMENT OVER THE PAST 12-24 HOURS, IS WHAT IS DRIVING THE DEGRADATION OF THE SYSTEM OVER THE PAST FEW HOURS. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON MSI, EIR, MICROWAVE AND RADAR DATA. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON A BLEND OF THE OBJECTIVE AND SUBJECTIVE CURRENT INTENSITY ESTIMATES NOTED ABOVE. EARLIER POSITIONS FROM 6 AND 12 HOURS AGO HAVE BEEN ADJUSTED HIGHER, SO THE CURRENT INTENSITY DEPICTS A SLIGHT WEAKENING OFF OF THE PEAK ASSESSED TO HAVE OCCURRED AT 130000Z. THE ENVIRONMENT REMAINS FAVORABLE OVERALL, WITH THE NOTED EXCEPTION OF THE HIGH UPPER-LEVEL SHEAR AND UPWELLING INDUCED SST COOLING. INITIAL WIND RADII BASIS: SAR DATA CURRENT STEERING MECHANISM: WEAK STEERING PATTERN WITH SUBTROPICAL RIDGING TO THE SOUTHWEST AND TO THE EAST, AND LOW-HEIGHT CENTERS OVER THE JAVA SEA AND SOUTH OF AUSTRALIA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.5 - 127 KTS KNES: T7.0 - 140 KTS DEMS: T6.0 - 115 KTS APRF: T6.0 - 115 KTS CIMSS SATCON: 108 KTS AT 130600Z CIMSS ADT: 129 KTS AT 130600Z CIMSS AIDT: 123 KTS AT 130600Z CIMSS D-MINT: 120 KTS AT 130527Z CIMSS D-PRINT: 134 KTS AT 130600Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD OTHER FACTORS: STRONG LOCALIZED RADIAL OUTFLOW ABOVE THE CORE OF THE SYSTEM. MODERATE TO HIGH SOUTHEASTERLY SHEAR AT THE OUTFLOW LAYER (200-400MB). 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: TC 17S (ZELIA) IS FORECAST TO CONTINUE DRIFTING SLOWLY OVER THE NEXT 12 HOURS, THOUGH A SLOWLY STRENGTHENING STEERING GRADIENT ON THE EAST SIDE SHOULD PUSH IT GENERALLY TOWARDS THE SOUTH-SOUTHWEST. A BUILDING STR MOVING WEST OF PAPUA NEW GUINEA OVER THE NEXT 24 TO 36 HOURS WILL STRENGTHEN GRADIENT ON THE EAST SIDE OF TC 17S, AND THE SYSTEM WILL START MOVING SOUTHWARD AT A SLIGHTLY GREATER PACE AFTER TAU 12. LANDFALL ALONG THE NORTHWEST COAST OF AUSTRALIA, BETWEEN PORT HEDLAND AND DAMPIER, IS EXPECTED AROUND TAU 36. THEREAFTER THE SYSTEM WILL CONTINUE TRACKING INLAND OVER WESTERN AUSTRALIA ALONG THE SOUTHWESTERN SIDE OF A NORTH-SOUTH ORIENTED RIDGE OVER CENTRAL AUSTRALIA. IN TERMS OF INTENSITY, THE ONGOING ERC WILL RESULT IN A GENERAL WEAKENING OF THE SYSTEM IN THE NEAR-TERM. IT IS CHALLENGING TO PREDICT THE LENGTH OF THE ERC BUT MORE THAN LIKELY IT WILL BE RATHER QUICK DUE TO VERY SMALL SIZE OF THE INNER-CORE OF TC 17S. OTHERWISE, CONDITIONS REMAIN FAVORABLE, AND ONCE THE ERC IS WRAPPED UP, THE SYSTEM IS EXPECTED TO QUICKLY REINTENSIFY. THE CURRENT FORECAST CALLS FOR A REINTENSIFICATION TO 140 KNOTS BY TAU 24, THOUGH THE ACTUAL PEAK COULD BE SLIGHTLY HIGHER AND OCCUR BETWEEN TAU 24 AND TAU 36, AS THE SYSTEM PASSES OVER A POOL OVER EXTREMELY WARM SSTS AND WITH HIGH OHC AND TAPS INTO EVEN STRONGER POLEWARD OUTFLOW CHANNEL. DEEP-LAYER SHEAR IS PREDICTED TO INCREASE SHARPLY RIGHT AS THE SYSTEM APPROACHES THE COAST, WHICH WILL WEAKEN IT SLIGHTLY AS IT CROSSES SHORE, BUT IT WILL REMAIN AN EXTREMELY STRONG AND DANGEROUS TC. RAPID WEAKENING OVER THE DESERTS OF WESTERN AUSTRALIA WILL OCCUR AFTER LANDFALL, WITH THE SYSTEM DISSIPATING BY TAU 72. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS ROUGHLY CONSTRAINED IN AN ENVELOPE FROM DAMPIER TO THE WEST TO PORT HEDLAND TO THE EAST, WITH THE MAJORITY OF THE RELIABLE GUIDANCE FOCUSED TIGHTLY NEAR THE MULTI-MODEL CONSENSUS MEAN. ENSEMBLE GUIDANCE IS A BIT MORE MIXED, WITH THE ECEPS IN PARTICULAR SHOWING A MUCH WIDER SPREAD IN POTENTIAL OUTCOMES, WITH SEVERAL MEMBERS TAKING THE SYSTEM WEST TO ABOUT 113E, THEN TURNING SOUTH AND RUNNING OVER LEARMONTH AND EXMOUTH, WHILE THE OTHER EXTREME MEMBERS TURN THE SYSTEM EASTWARD UP TOWARDS BROOME. THE BULK OF THE ECEPS MEMBERS LIE BETWEEN A MIDPOINT BETWEEN DAMPIER AND LEARMONTH AND PORT HEDLAND. THE GEFS ON THE OTHER HAND IS MUCH MORE CONSTRAINED, WITH ALL MEMBERS CONSISTENT WITH THE DETERMINISTIC ENVELOPE, BETWEEN ROUGHLY DAMPIER AND PORT HEDLAND. THE JTWC FORECAST LIES CLOSE TO THE CONSENSUS MEAN AND CONSISTENT WITH THE PREVIOUS FORECAST BUT DUE TO THE WEAK STEERING ENVIRONMENT AND CONTINUED ENSEMBLE UNCERTAINTY, IT IS SET WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS FOR THE MOST PART CONSISTENT IN SHOWING A FLAT TREND FOR THE FIRST 6-12 HOURS, FOLLOWED BY REINTENSIFICATION THROUGH TAU 24-36. THE JTWC FORECAST IS CONSISTENT WITH THE HAFS-A TREND WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN