WDXS32 PGTW 131500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (GEZANI) WARNING NR 012// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 22.5S 36.4E INITIAL INTENSITY: 90 KTS GEOGRAPHIC REFERENCE: 212 NM WEST OF EUROPA ISLAND MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 30 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES TROPICAL CYCLONE (TC) 21S (GEZANI) HAS REACHED ITS CLOSEST POINT OF APPROACH TO THE MOZAMBIQUE COASTLINE NORTHEAST OF MAXIXE AND IS NOW SLIDING SOUTHWARD ON A COURSE PARALLEL TO THE COASTLINE. THE SYSTEM IS MAINTAINING A RAGGED 10NM WIDE EYE, HOWEVER CLOUD TOP TEMPERATURES HAVE WARMED CONSIDERABLY OVER THE PAST SIX HOURS, WHILE THE EYE TEMPERATURE HAS ALSO WARMED. DEEP CONVECTION IS UNDERGOING CYCLIC DEVELOPMENT, CURRENTLY RE-ORGANIZING AROUND THE PRIMARY VORTEX. A 131138Z GMI 89GHZ MICROWAVE IMAGE REVEALED A WELL-DEFINED MICROWAVE EYE, WITH A CONVECTIVELY ROBUST EASTERN EYEWALL AND A DEGRADED WESTERN EYEWALL, AS WELL AS A POSSIBLE SECONDARY EYEWALL ON THE EASTERN FLANK OF THE INNER-CORE. COMPARISON WITH THE 36GHZ CHANNEL REVEALS APPROXIMATELY 8NM OF EASTWARD VERTICAL VORTEX TILT, SUGGESTING MODERATE WESTERLY SHEAR IN THE MID-LEVELS, ALTHOUGH ANALYSIS INDICATES DEEP-LAYER SHEAR REMAINS LOW. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE MICROWAVE CENTER-FIX NOTED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, CONSISTENT WITH MULTI-PLATFORM OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES. ENVIRONMENTAL CONDITIONS ARE GENERALLY FAVORABLE, CHARACTERIZED BY LOW DEEP-LAYER SHEAR, HIGH OCEAN HEAT CONTENT (OHC), AND STRONG RADIAL OUTFLOW ALOFT. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T5.0 - 90 KTS DEMS: T5.0 - 90 KTS FMEE: T5.0 - 90 KTS CIMSS ADT: 87 KTS AT 131030Z CIMSS D-MINT: 79 KTS AT 131141Z CIMSS D-PRINT: 90 KTS AT 131100Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 21S IS SITUATED NEAR THE SUBTROPICAL RIDGE (STR) AXIS, TRACKING DUE SOUTHWARD ALONG THE COASTAL MARGIN OF MOZAMBIQUE. THE ASSOCIATED LOW-LEVEL CIRCULATION CENTER (LLCC) IS FORECAST TO TRACK APPROXIMATELY 20-30NM OFFSHORE OF MAXIXE WITHIN THE NEXT 6 TO 12 HOURS. THE SYSTEM WILL SUBSEQUENTLY TURN SOUTHEASTWARD UPON ROUNDING THE RIDGE AXIS BEFORE TURNING SHARPLY EASTWARD BY TAU 36 AS IT BEGINS TO INTERACT WITH A STRONG MID-LATITUDE TROUGH APPROACHING FROM THE SOUTHWEST. AT THIS JUNCTURE, THE AMPLITUDE OF THE TROUGH AND THE ADVECTION SPEED OF TC 21S WILL BE THE PRIMARY DETERMINANTS OF THE TRACK GEOMETRY. CONSISTENT WITH PRIOR MODEL CYCLES, ECMWF AND GALWEM DEPICT A ZONAL ELONGATION OF THE STR, LEADING TC 21S TO REMAIN STEERED BY THE STR OVER SOUTHERN AFRICA AND UNDERGO A RETROGRADE LOOP EQUATORWARD. CONVERSELY, THE GFS DEPICTS PROMPT RECURVATURE AND A STRONGER TROUGH, RESULTING IN THE SYSTEM ACCELERATING EASTWARD BEFORE TRACKING SOUTHEASTWARD AND BEING ABSORBED INTO THE TROUGH PATTERN. THE REMAINDER OF THE GLOBAL AND AI MODELS SUGGEST A CONSENSUS TRAJECTORY EAST-NORTHEASTWARD AFTER TAU 36, BEFORE BEING CAPTURED BY THE TROUGH AND ACCELERATING POLEWARD AFTER TAU 72. GIVEN THE BIFURCATION IN MODEL GUIDANCE, UNCERTAINTY IS HIGH; THE JTWC FORECAST ALIGNS WITH THE MULTI-MODEL CONSENSUS. REGARDING INTENSITY, MARGINAL INTENSIFICATION IS EXPECTED OVER THE NEXT 12 HOURS. THEN MAINTAIN INTENSITY THROUGH TAU 24. RAPID WEAKENING WILL BEGIN AFTER TAU 36 AS SHEAR IS EXPECTED TOO RAPIDLY INCREASE IN CONJUNCTION WITH SEVERE DRY AIR ENTRAINMENT, EFFECTIVELY DECAPITATING THE VORTEX AFTER TAU 48. THE SYSTEM THEN WEAKENS STEADILY BUT MORE SLOWLY AFTER TAU 72 AS THE REMNANT VORTEX SLOWLY SPINS DOWN. TC 21S WILL BEGIN SUBTROPICAL TRANSITION (STT) BY THE END OF THE FORECAST IS THE SHALLOW WARM-CORE VORTEX, CAPPED BY A DEEP LAYER OF DRY AIR, MOVES INTO COOLER WATERS. MODEL DISCUSSION: TRACK GUIDANCE REMAINS VERY CONSISTENT IF ALSO HIGHLY UNCERTAIN. THE GALWEM AND ECMWF MAINTAIN A SOLUTION FEATURING A COUNTER-CLOCKWISE LOOP AFTER TAU 36. MEANWHILE, THE GFS AND GEFS MEAN PUSH THE SYSTEM TO THE SOUTHEAST OF MADAGASCAR BY TAU 72, THEN CHECKMARK BACK TO THE SOUTHWEST THROUGH TAU 120. THE CONSENSUS, INCLUDING AI-DERIVED GUIDANCE AND THE ECMWF-AIFS, SHOW THE SYSTEM COMMENCING AN EQUATORWARD RECURVATURE SIMILAR TO THE ECMWF BUT EXECUTING A SHARP POLEWARD TURN AT TAU 72. TOTAL CROSS-TRACK SPREAD BETWEEN THE GFS AND ECMWF OUTLIERS IS 1100NM, BUT A MUCH MORE MODEST SPREAD OF 340NM BETWEEN THE REMAINDER OF THE GUIDANCE AT TAU 120. THE JTWC FORECAST IS PLACED NEAR THE AI CONSENSUS THROUGH TAU 72, THEN CONSISTENT WITH THE EC-AIFS TRACKER THROUGH TAU 120. CONFIDENCE IS MEDIUM TO TAU 72, AND LOW THROUGH TAU 120. INTENSITY GUIDANCE IS GOOD AGREEMENT, THOUGH THE HAFS-A DEPICTS THE SYSTEM INTENSIFYING UP TO 105 KNOTS BY TAU 12. THE REMAINDER OF THE PACKAGE SHOWS A PEAK AROUND 95 KNOTS, THEN FAIRLY RAPID WEAKENING FROM TAU 24 THROUGH THE REMAINDER OF THE FORECAST PERIOD. THE JTWC FORECAST IS PLACED ABOUT ON THE CONSENSUS MEAN THROUGH TAU 24, THEN CLOSE TO THE HAFS-A. CONFIDENCE IS MEDIUM TO TAU 72, AND LOW THROUGH TAU 120. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN