WDXS32 PGTW 121500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (GEZANI) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 20.4S 40.0E INITIAL INTENSITY: 75 KTS GEOGRAPHIC REFERENCE: 109 NM NORTH OF EUROPA ISLAND MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 11 KTS SIGNIFICANT WAVE HEIGHT: 34 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL CYCLONE (TC) 21S (GEZANI) IS CURRENTLY UNDERGOING ANOTHER ROUND OF RAPID INTENSIFICATION (RI), INTENSIFYING OVER 35 KNOTS SINCE MOVING OFF THE WEST COAST OF MADAGASCAR. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT STORM, WITH A WELL-DEFINED, CLOUD-COVERED EYE, WITH VERTICAL HOT TOWERS (VHTS) DEVELOPING AROUND THE LOW-LEVEL CIRCULATION CENTER (LLCC). ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) SHOWS A WARMING EYE, THOUGH EYE TEMPS ARE STILL IN THE -35C RANGE DUE TO THE CIRRUS COVER OVER THE EYE. A 121046Z AMSR2 89GHZ IMAGE REVEALED A SOLID RING OF DEEP CONVECTION AROUND THREE-QUARTERS OF THE LLCC, THOUGH THE EYEWALL WAS OPEN ON THE SOUTHWESTERN, UPSHEAR FACING QUADRANT. SUBSEQUENT EIR IMAGERY SUGGESTS THIS GAP IN THE EYEWALL IS CLOSING, WITH DEEP CONVECTION AND VHTS WRAPPING INTO THE SOUTHWESTERN QUADRANT. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE IN THE MSI AND EXTRAPOLATION OF THE LOW-LEVEL MICROWAVE EYE IN THE 36GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, CONSISTENT WITH THE BULK OF THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES NOTED BELOW. THE ACTUAL INTENSITY MAY BE A FEW KNOTS HIGHER, CLOSER TO THE AIDT WHICH TENDS TO PERFORM BETTER DURING RI PHASES AND DUE TO THE FACT THAT THE ADT IS NOT TRACKING THE EYE. ENVIRONMENTAL CONDITIONS ARE OPTIMAL FOR RI, CHARACTERIZED BY MINIMAL VERTICAL WIND SHEAR (VWS), SYMMETRIC RADIAL OUTFLOW ALOFT, AND ELEVATED OCEAN HEAT CONTENT (OHC) PROVIDING AMPLE THERMODYNAMIC ENERGY. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS DEMS: T4.5 - 77 KTS FMEE: T4.5 - 77 KTS CIMSS SATCON: 76 KTS AT 121200Z CIMSS ADT: 74 KTS AT 121200Z CIMSS AIDT: 87 KTS AT 121200Z CIMSS D-MINT: 74 KTS AT 121047Z CIMSS D-PRINT: 70 KTS AT 121230Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 0-5 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: THE FIRST 36 TO 48 HOURS OF THE FORECAST IS PLACED WITH FAIRLY HIGH CERTAINTY, AS THE SYSTEM WILL TRACE A ROUTE AROUND THE STR AXIS, REACHING THE RIDGE AXIS NEAR TAU 36. AT THIS POINT THE SYSTEM WILL REACH ITS CLOSEST POINT TO LANDFALL, APPROXIMATELY 30NM EAST OF MAXIXE, MOZAMBIQUE. THE PERIPHERAL WINDS OF THE INNER CORE OF THE SYSTEM MAY BRUSH THE COASTLINE, THOUGH THE VORTEX CORE IS EXPECTED TO REMAIN OFFSHORE. THE SYSTEM SUBSEQUENTLY RECURVES SOUTHEASTWARD BY TAU 48 UPON ROUNDING THE RIDGE AXIS. BEYOND THIS PERIOD, TRACK UNCERTAINTY INCREASES SIGNIFICANTLY, AS A 180- DEGREE BIFURCATION MANIFESTS WITHIN THE MODEL GUIDANCE, DRIVEN BY DIVERGENT KINEMATIC REPRESENTATIONS OF THE SYNOPTIC STEERING PATTERN. THE PRIMARY DETERMINANTS ARE TRACK SPEED AND THE AMPLITUDE OF AN APPROACHING MAJOR SHORTWAVE TROUGH TO THE SOUTH. THE EUROPEAN SUITE DEPICTS THE CENTER OF TC 21S TRANSITING BRIEFLY OVER TERRAIN, INDUCING FRICTIONAL DECELERATION SUFFICIENT TO PREVENT CAPTURE BY THE POLEWARD TROUGH, WHICH IS RELATIVELY ATTENUATED IN THE EUROPEAN MODELS; THE SYSTEM IS SUBSEQUENTLY ADVECTED EQUATORWARD UNDER THE INFLUENCE OF A BUILDING RIDGE OFF SOUTH AFRICA. CONVERSELY, THE GFS SUITE MAINTAINS AN OFFSHORE TRAJECTORY, PRESERVING TRANSLATIONAL VELOCITY AND RESULTING IN TROUGH CAPTURE AND RAPID SOUTHEASTWARD ADVECTION. ARTIFICIAL INTELLIGENCE (AI) GUIDANCE SUGGESTS A BLENDED SCENARIO CHARACTERIZED BY AN OFFSHORE TRACK PARALLEL TO MOZAMBIQUE, FOLLOWED BY MODERATE EASTWARD ADVECTION ALONG THE TROUGH PERIPHERY BEFORE EXECUTING A SHARP POLEWARD TURN BY THE END OF THE FORECAST. THE JTWC FORECAST ADOPTS THE BLENDED APPROACH, FAVORING THE AI GUIDANCE, THOUGH UNCERTAINTY IN THE EXTENDED FORECAST IS EXTREMELY HIGH. REGARDING INTENSITY, THE ENVIRONMENT IS PRIME FOR RI; THE FORECAST ANTICIPATES CONTINUED INTENSIFICATION TO A MINIMUM OF 110 KNOTS BY TAU 36. A HIGHER MAGNITUDE PEAK REMAINS PLAUSIBLE, DUE TO THE COMPACT NATURE OF THE SYSTEM. POST-RECURVATURE, THE SYSTEM WILL DEGENERATE GRADUALLY, WITH ACCELERATED CYCLOLYSIS EXPECTED AFTER TAU 72 DUE TO STRONG WESTERLY SHEAR AND MID-LEVEL DRY AIR ENTRAINMENT. MODEL DISCUSSION: NUMERICAL WEATHER PREDICTION (NWP), AI, AND ENSEMBLE GUIDANCE EXHIBIT STRONG CORRELATION THROUGH TAU 48, WITH CONSENSUS ENVELOPE WIDTH CONSTRAINED TO 95NM. ECMWF REPRESENTS THE WESTERN BOUNDARY, TRACKING THE SYSTEM ALONG THE MOZAMBIQUE LITTORAL FROM TAU 36 TO TAU 48, WHILE THE GFS CONSTITUTES THE EASTERN EDGE. THE ECMWF SUITE IS ALSO THE TRANSLATIONAL MINIMUM THROUGH TAU 48, LAGGING THE GFS BY 150NM. POST-TAU 48, THE ECMWF AND ITS ENSEMBLE MEAN REDIRECT EQUATORWARD, POSITIONING THE VORTEX EAST OF BEIRA BY TAU 120. THE GFS MEANWHILE ACCELERATES SOUTHEASTWARD, REACHING A TERMINUS 1300NM TO THE SOUTHEAST. THE REMAINDER OF THE DYNAMICAL PACKAGE TRACKS GENERALLY EASTWARD THROUGH TAU 96 FOLLOWED BY A DISCRETE POLEWARD TURN. NEVERTHELESS, A 400NM VARIANCE PERSISTS BETWEEN AI MODELS, GALWEM, AND NAVGEM. ENSEMBLES DEPICT EXTREME UNCERTAINTY, WITH INTRA-MEMBER SPREAD EXCEEDING 2000NM BY TAU 120. THE JTWC FORECAST ALIGNS WITH THE MULTI-MODEL CONSENSUS THROUGH TAU 48 WITH HIGH CONFIDENCE, TRANSITIONING TO THE GDM FNV3 THEREAFTER. CONFIDENCE IN THE EXTENDED TAUS IS EXTREMELY LOW. INTENSITY GUIDANCE IS LARGELY CONGRUENT, THOUGH ANOMALOUSLY, COAMPS-TC (GFS/NAVGEM) INDICATES NEGLIGIBLE ADDITIONAL INTENSIFICATION. HWRF AND HAFS-A PROJECT PEAKS BETWEEN 100-110 KNOTS, WHILE MULTIPLE RI AIDS (RIDE, DTOP) INDICATE MAGNITUDES APPROACHING 130 KNOTS. THE JTWC FORECAST REMAINS MARGINALLY BELOW THE MOST AGGRESSIVE RI AIDS, SYNCHRONIZED WITH HAFS-A THROUGH PEAK INTENSITY. CONFIDENCE IS MEDIUM THROUGH TAU 72, SUBSEQUENTLY LOW, AS THE THERMODYNAMIC EVOLUTION IS CONTINGENT UPON THE TRACK SCENARIO. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN