WDXS31 PGTW 052100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 12S (JENNA) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.4S 96.1E INITIAL INTENSITY: 65 KTS GEOGRAPHIC REFERENCE: 140 NM SOUTH-SOUTHWEST OF THE COCOS ISLANDS MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 12 KTS SIGNIFICANT WAVE HEIGHT: 25 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL CYCLONE (TC) 12S (JENNA) HAS STEADILY INTENSIFIED OVER THE PAST 12 HOURS, UNDER ATMOSPHERIC AND OCEANIC ENVIRONMENTAL CONDITIONS. AN EARLIER SAR PASS APPROXIMATELY 1200Z INDICATED A MAXIMUM 1-MIN WIND OF 54 KNOTS AND THE SYSTEM HAS EXHIBITED CONTINUED STRUCTURAL ORGANIZATION SINCE THAT TIME. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT CENTRAL DENSE OVERCAST (CDO) FEATURE, WHICH DISPLAYS INCIPIENT ROTATIONAL CHARACTERISTICS. A SLIGHT WARMING OF CLOUD TOPS IS NOTED, PARTICULARLY ALONG THE EASTERN SIDE OF THE CDO ATTRIBUTED TO THE ENTRAINMENT OF DRIER MID-LEVEL AIR AND SLIGHTLY ELEVATED EASTERLY VERTICAL WIND SHEAR. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE REFLECTING A LACK OF RECENT MICROWAVE IMAGERY AND IS POSITIONED AT THE NEXUS OF MAXIMUM ROTATION EMBEDDED WITHIN THE CDO FEATURE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE. THIS ASSESSMENT IS SET SLIGHTLY ABOVE THE CONSENSUS OF AGENCY DVORAK CURRENT INTENSITY ESTIMATES, SUPPORTED BY SATELLITE-DERIVED INTENSITY ESTIMATES FROM CIMSS (D- PRINT, D-MINT, AND SATCON) AND THE OBSERVED ENHANCEMENT OF THE CONVECTIVE ARCHITECTURE. ENVIRONMENTAL CONDITIONS REMAIN CONDUCIVE FOR DEVELOPMENT, CHARACTERIZED BY LOW VERTICAL WIND SHEAR, ROBUST POLEWARD OUTFLOW, AND WARM SEA SURFACE TEMPERATURES (SSTS). INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) CENTERED OVER WESTERN AUSTRALIA. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS DEMS: T3.5 - 55 KTS APRF: T3.5 - 55 KTS CIMSS SATCON: 71 KTS AT 051845Z CIMSS ADT: 53 KTS AT 051730Z CIMSS AIDT: 38 KTS AT 051730Z CIMSS D-MINT: 70 KTS AT 051845Z CIMSS D-PRINT: 68 KTS AT 051830Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 27-28 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: DRY LOW- TO MID-LEVEL AIR ALONG THE EASTERN FLANK. ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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: SINCE PASSING EAST OF COCOS ISLAND, TC 12S HAS MAINTAINED A SOUTH-SOUTHWESTERLY TRACK, STEERED BY THE NORTHWESTERN PERIPHERY OF A DEEP-LAYER STR CENTERED OVER WESTERN AUSTRALIA. THE SYSTEM IS FORECAST TO TRACE A GENTLE SOUTHWESTWARD ARC OVER THE NEXT 36 HOURS AS THE STR AMPLIFIES WHILE MAINTAINING ITS NORTHWEST- SOUTHEAST ORIENTATION. ENVIRONMENTAL CONDITIONS WILL REMAIN FAVORABLE (LOW TO MODERATE SHEAR, WARM SSTS, AND EFFECTIVE POLEWARD OUTFLOW) FOR THE NEXT 36 HOURS, ALLOWING FOR CONTINUED INTENSIFICATION TO A PEAK INTENSITY OF 70-75 KNOTS BY TAU 36. HOWEVER, THE WINDOW FOR INTENSIFICATION IS LIMITED. BY TAU 24, VERTICAL WIND SHEAR IS PROJECTED TO INCREASE, INITIALLY AT A GRADUAL RATE BEFORE ACCELERATING AFTER TAU 30. BY TAU 36, SHEAR IS EXPECTED TO EXCEED 35 KNOTS. THE COMBINATION OF PROHIBITIVE SHEAR AND AN INFLUX OF EXCEPTIONALLY DRY MID-LEVEL AIR IS EXPECTED TO DECOUPLE THE DEEP CONVECTION FROM THE LOW-LEVEL CIRCULATION, INDUCING RAPID WEAKENING THEREAFTER. AS THE VORTEX DECREASES IN VERTICAL DEPTH AND WEAKENS, IT WILL COME UNDER THE STEERING INFLUENCE OF THE LOWER-LEVEL EASTERLY FLOW ALONG THE NORTHERN PERIPHERY OF AN EXTENSIVE RIDGE TO THE SOUTH. THE SYSTEM WILL TRACK WESTWARD FROM TAU 48 ONWARDS, AS IT UNDERGOES RAPID WEAKENING AND ULTIMATELY DISSIPATES BY TAU 96. MODEL DISCUSSION: DETERMINISTIC, ENSEMBLE AND ARTIFICIAL INTELLIGENCE MODELS EXHIBIT STRONG CONSENSUS ON THE OVERALL TRACK SCENARIO. THROUGH THE INFLECTION POINT AT TAU 36, MODEL GUIDANCE IS TIGHTLY CLUSTERED WITHIN A 50NM WIDE ENVELOPE. AFTER THE SYSTEM TURNS WESTWARD AT TAU 48, CROSS-TRACK INCREASES TO APPROXIMATELY 150NM, WITH THE NAVGEM AND EGRR MODELS POSITIONED ON THE NORTHERN EDGE, AND THE ECMWF AND ECEPS MEAN ON THE SOUTHERN EDGE OF THE ENVELOPE. MORE SIGNIFICANTLY, SUBSTANTIAL INCREASE IN ALONG-TRACK SPREAD IS NOTED AFTER TAU 48, WITH THE GFS-GEFS SUITE EXHIBITING A MUCH FASTER FORWARD SPEED THAN THE ECMWF-ECEPS PAIRING, RESULTING IN ALONG-TRACK UNCERTAINTY EXCEEDING 400NM BY THE END OF THE FORECAST PERIOD. THE JTWC OFFICIAL FORECAST IS POSITIONED NEAR THE EC-AIFS CONSENSUS AND SLIGHTLY SLOWER THAN THE MULTI-MODEL CONSENSUS MEAN, WITH HIGH CONFIDENCE. INTENSITY GUIDANCE CONCURS THAT THE SYSTEM WILL REACH PEAK INTENSITY AT OR BEFORE TAU 24, THEN RAPIDLY WEAKEN THROUGH THE REMAINDER OF THE FORECAST PERIOD. THE HAFS-A, HOWEVER, DOES INDICATE A POTENTIAL FOR REINTENSIFICATION AFTER TAU 72, THOUGH IT IS A SINGULAR OUTLIER IN THIS REGARD. THE JTWC FORECAST FOLLOWS THE CONSENSUS MEAN TREND, BUT IS MAINTAINED APPROXIMATELY 5 KNOTS HIGHER THROUGH THE FORECAST PERIOD, WITH HIGH CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: HIGH INTENSITY 00-72 HR: HIGH INTENSITY 72-120 HR: MEDIUM// NNNN