WDXS31 PGTW 281500 AMD MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING NR 012A AMENDED// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.2S 94.6E INITIAL INTENSITY: 110 KTS GEOGRAPHIC REFERENCE: 328 NM SOUTH-SOUTHWEST OF THE COCOS ISLANDS MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 11 KTS SIGNIFICANT WAVE HEIGHT: 43 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL CYCLONE (TC) 27S (COURTNEY) HAS RAPIDLY INTENSIFIED OVER THE PAST SIX HOURS, AND ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWING THE SYSTEM DEVELOPING A PINHOLE EYE FEATURE. THE EYE BEGAN TO EMERGE AT 1000Z, REACHED ITS PEAK AROUND 1200Z AND IN THE SUBSEQUENT HOUR HAS BEGUN TO COOL AND BECOME A BIT MORE RAGGED. HOWEVER, 89GHZ COLOR ENHANCED MICROWAVE IMAGERY FROM A 281126 WSF-M PASS AND A 281215Z SSMIS PASS REVEAL BEAUTIFULLY SYMMETRICAL MICROWAVE EYE FEATURE, WITH A STRONG EYEWALL ALONG THE WESTERN HALF OF THE EYE, BUT THE EASTERN SIDE IS MUCH WEAKER OR EVEN OPEN IN THE SSMIS IMAGE. COMPARISON WITH THE 37GHZ IMAGE IN THE WSF-M DATA SHOWS A SLIGHT WESTWARD VORTEX TILT WITH HEIGHT, DUE TO MID-LEVEL MODERATE SHEAR. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE 36GHZ MICROWAVE IMAGERY FROM THE PASSES NOTED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, USING A BLEND OF THE AGENCY FIXES NOTED ABOVE. PGTW BROKE CONSTRAINTS TO OBTAIN THE T6.0 ESTIMATE, WHILE THE OTHER AGENCIES DID NOT ALTHOUGH THEY DID OBTAIN DT VALUES OF T6.0. THE OBJECTIVE ESTIMATES ARE SLOWLY CATCHING UP BUT ARE FOR THE MOST PART NOT TRACKING THE EYE AND STILL USING UNIFORM CDO METHOD. THE ENVIRONMENT REMAINS FAVORABLE, WITH LOW DEEP-LAYER SHEAR, WARM SSTS AND GOOD RADIAL OUTFLOW ALOFT. SLIGHTLY HIGHER MID-LEVEL SHEAR IS STILL A FACTOR HOWEVER, EVIDENCED BY THE OPEN EYEWALL ON THE UPSHEAR SIDE OF THE VORTEX. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.0 - 115 KTS KNES: T5.5 - 102 KTS DEMS: T5.5 - 102 KTS APRF: T5.5 - 102 KTS CIMSS SATCON: 66 KTS AT 280940Z CIMSS ADT: 59 KTS AT 281140Z CIMSS AIDT: 48 KTS AT 281140Z CIMSS D-MINT: 82 KTS AT 281217Z CIMSS D-PRINT: 75 KTS AT 281230Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 26-27 CELSIUS OUTFLOW: STRONG RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS IS AN AMENDED FORECAST, UPDATED TO REFLECT THE ONSET OF RAPID INTENSIFICATION WHICH HAS LED TO AN INCREASE OF 25 KNOTS IN THE INITIAL INTENSITY BEYOND THE EXPECTED INTENSITY IN THE PREVIOUS FORECAST. FORECAST DISCUSSION: THERE HAS BEEN NO SIGNIFICANT CHANGE IN THE FORECAST TRACK SINCE THE PREVIOUS REGULAR FORECAST ISSUANCE. THE SYSTEM WILL ARC SOUTHWESTWARD TO SOUTH OVER THE NEXT 72 HOURS AS IT ROUNDS THE AXIS OF THE RIDGE WHICH IS SHIFTING TO A POSITION SOUTHEAST OF TC 27S. THE SYSTEM SLOWS DOWN AFTER TAU 72 AS IT BEGINS TO RUN INTO A LOW- TO MID-LEVEL RIDGE FIRMLY ENTRENCHED TO THE SOUTH. THE SYSTEM IS LIKELY TO INTENSIFY A BIT MORE OVER THE NEXT 12 HOURS OR SO, WITH THE FORECAST CALLING FOR A PEAK OF 115 KNOTS BY TAU 12 THEN HOLDING STEADY THROUGH TAU 24. THE SYSTEM IS QUITE COMPACT AND THUS PRONE TO RAPID FLUCTUATIONS IN INTENSITY, AND RAPID EYEWALL REPLACEMENT CYCLES (ERC), WHICH COULD IMPACT THE INTENSITY FORECAST. THE CURRENT M-PERC ERC PROBABILITY IS LESS THAN 10 PERCENT BUT LIKELY TO QUICKLY RAMP UP DUE TO THE RAPID INTENSIFICATION (RI). REGARDLESS, THE SYSTEM HAS A BIT MORE LEFT IN THE TANK BUT AFTER TAU 24, SHEAR WILL BEGIN TO INCREASE SHARPLY AS A TROUGH APPROACHES FROM THE SOUTHWEST. BY TAU 36, SHEAR BEGINS TO PICK UP, AND SHARPLY INCREASES BEYOND TAU 48 AS THE SYSTEM MOVES SOUTH OF THE 26C ISOTHERM. THE SYSTEM WILL BE SHEARED APART AFTER TAU 72 AS SHEAR INCREASES TO MORE THAN 40 KNOTS, BEGINNING A RAPID WEAKENING PHASE. DRY AIR BEGINS TO INTRUDE FROM THE NORTH JUST AFTER TAU 72 AND WILL COMPLETELY ENGULF THE VORTEX SHORTLY THEREAFTER, DOOMING TC 27S TO SLOW DEMISE. SHORTLY AFTER TAU 72, THE SYSTEM WILL BEGIN TO TRANSITION TO A SUBTROPICAL LOW (STT), HOWEVER, IT IS FORECAST THAT IT WILL BE RAPIDLY WEAKENING AT THE SAME TIME AND THAT IT WILL DISSIPATE PRIOR TO COMPLETING STT. AS THE SYSTEM WEAKENS BELOW TROPICAL STORM STRENGTH, THE REMNANT VORTEX WILL MAKE A SHARP TURN WESTWARD, STEERED BY THE SOUTHEASTERLY FLOW EMANATING FROM THE STRONG RIDGE TO THE SOUTH. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS, FOR THE MOST PART, IN GOOD AGREEMENT. THE BULK OF THE GUIDANCE IS CONTAINED WITHIN A RELATIVELY TIGHT ENVELOPE AND SHOWS AGREEMENT ON THE OVERALL TRACK SHAPE AND TRACK SPEEDS. THE TWO SIGNIFICANT OUTLIERS ARE THE GALWEM AND UKMET ENSEMBLE MEAN WHICH DEPICT THE SYSTEM TRACKING STRAIGHT SOUTHWESTWARD AFTER TAU 72 WHILE THE REMAINDER OF THE GUIDANCE TURNS SOUTH-SOUTHEASTWARD. THE JTWC FORECAST IS CONSISTENT WITH THE ORIGINAL, NON-AMENDED FORECAST AND THE CONSENSUS MEAN WITH HIGH CONFIDENCE THROUGH TAU 72, AND MEDIUM THEREAFTER. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM WILL EITHER MAINTAIN CURRENT INTENSITY OR INTENSIFY ANOTHER FIVE KNOTS OR SO, THEN FLATTEN OUT FOR ANOTHER 12 HOURS BEFORE WEAKENING STEADILY THROUGH THE REMAINDER OF THE FORECAST. THE TWO EXCEPTIONS ARE THE DTOP RI AID WHICH TAKES TC 27S TO A LOFTY PEAK OF 140 KNOTS IN 18 HOURS AND THE HAFS-A WHICH PEAKS THE SYSTEM AT 125 KNOTS. BOTH SEEM OVERLY AGGRESSIVE AND NOT VERY LIKELY BUT CANNOT BE DISCOUNTED ENTIRELY. THE JTWC FORECAST IS CONSISTENT WITH THE MULTI-MODEL CONSENSUS MEAN THROUGH THE ENTIRE FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM 4. JUSTIFICATION FOR AMENDMENT: UPDATED THE INITIAL INTENSITY AND FORECAST INTENSITY.// NNNN