WDXS31 PGTW 210900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 22S (HORACIO) WARNING NR 004// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.6S 73.4E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 572 NM SOUTH OF DIEGO GARCIA MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 13 KTS SIGNIFICANT WAVE HEIGHT: 16 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY EXPOSED, ELONGATED AND POORLY ORGANIZED LOW LEVEL CIRCULATION (LLC), WITH MULTIPLE VORTICES EMBEDDED WITHIN THE LARGER ROTATION. BROADER ROTATION. PERSISTENT DEEP CONVECTION HAS BEEN OBSERVED; HOWEVER, IT REMAINS DISPLACED SUBSTANTIALLY WEST OF THE LLCC DUE TO MODERATE TO STRONG EASTERLY VERTICAL WIND SHEAR AND THE ENTRAINMENT OF DRY MID- LEVEL AIR INTO THE EASTERN EXTENT OF THE CIRCULATION. A 210413Z MHS 89GHZ MICROWAVE IMAGE INDICATED SHALLOW BANDING FEATURES ENCIRCLING THE MAJORITY OF THE LLCC, WHILE DEEP CONVECTION IS CONCENTRATED IN THE WESTERN SECTOR. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE, PLACED WITHIN THE APPROXIMATE CENTROID OF THE MULTIPLE VORTICES EVIDENT IN THE ANIMATED MSI. A 210337Z ASCAT-B PARTIAL PASS DETECTED 30-34 KNOT WINDS CONFINED TO THE SOUTHWESTERN PORTION OF THE CIRCULATION, SUPPORTING THE INITIAL INTENSITY ESTIMATE WITH HIGH CONFIDENCE. ENVIRONMENTAL CONDITIONS ARE MARGINALLY CONDUCIVE, WITH WARM SSTS AND MODERATE POLEWARD OUTFLOW ALOFT COUNTERACTED BY MODERATE EASTERLY SHEAR AND DRY AIR ENTRAINMENT. 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: T3.0 - 45 KTS FMEE: T3.0 - 45 KTS CIMSS ADT: 34 KTS AT 210600Z CIMSS AIDT: 33 KTS AT 210600Z CIMSS D-PRINT: 31 KTS AT 210600Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-20 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: HIGHER MID-LEVEL SHEAR AND MID-LEVEL DRY AIR ENTRAINMENT IN THE NORTHEASTERN QUADRANT. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 22S (HORACIO) IS FORECAST TO TRACK WEST-SOUTHWESTWARD ALONG AN EXTENSION OF THE DEEP STR POSITIONED FAR TO THE SOUTHEAST OVER THE NEXT 12 TO 24 HOURS. AFTER TAU 24, THE SYSTEM WILL GRADUALLY TURN SOUTHWARD AS IT TRAVERSES THE NORTHWESTERN AND THEN WESTERN ASPECT OF THE STR. TC 22S WILL REACH THE RIDGE AXIS BY APPROXIMATELY TAU 72, THEN ACCELERATE SOUTHEASTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD AS IT BEGINS TO INTERACT WITH THE SUBTROPICAL WESTERLIES. REGARDING INTENSITY, THE SYSTEM IS FORECAST TO REMAIN RELATIVELY STEADY FOR THE NEXT 12 TO 24 HOURS, AS SHEAR IS ANTICIPATED TO REMAIN AT MODERATE LEVELS AND DRY MID-LEVEL AIR WILL CONTINUE TO INTRUDE INTO THE CORE OF THE SYSTEM DURING THIS TIME. BY TAU 24, SHEAR IS FORECAST TO BEGIN TO DECREASE, WHICH WILL FACILITATE VORTEX ALIGNMENT AND SYMMETRIZATION. ONCE THESE PROCESSES COMPLETE, SHORTLY AFTER TAU 36, TC 22S WILL BEGIN TO RAPIDLY INTENSIFY AS IT TAPS INTO A STRONG POLEWARD OUTFLOW CHANNEL. THE SYSTEM IS FORECAST TO REACH PEAK INTENSITY OF 100 KNOTS AT TAU 72 AS IT REACHES THE RIDGE AXIS AND BEGINS ITS TURN SOUTHWARD. SHORTLY AFTER TAU 72, NORTHERLY SHEAR IS FORECAST TO RAPIDLY INCREASE, WITH VORTEX DECOUPLING ANTICIPATED BY TAU 96. BY THE END OF THE FORECAST, THE SYSTEM WILL BEGIN TO INTERACT WITH A DEEP MID-LATITUDE TROUGH, BECOME COMPLETELY ENVELOPED BY DRY AIR ABOVE 700MB AND MOVE UNDER A JET MAXIMUM, MARKING THE ONSET OF EXTRATROPICAL TRANSITION (ETT). MODEL DISCUSSION: DETERMINISTIC, ENSEMBLE AND ARTIFICIAL INTELLIGENCE (AI) MODELS ARE IN GOOD AGREEMENT ON THE OVERALL TRACK SCENARIO, PARTICULARLY THROUGH TAU 72, WHERE THE GUIDANCE DEPICTS A 175NM CROSS-TRACK SPREAD BETWEEN THE GFS ON THE WESTERN EDGE AND ECMWF ON THE EASTERN EDGE OF THE ENVELOPE. BEYOND TAU 72, THE MODELS DIVERGE, WITH THE GFS TRACKING THE SYSTEM SOUTH-SOUTHWEST, WHILE THE GALWEM, EGRR AND ECMWF ENSEMBLE TRACK THE CENTER DUE SOUTH, AND THE ECMWF AND THE AI MODELS DEPICT A GRADUAL RECURVE SCENARIO TRACKING THE SYSTEM SOUTHEASTWARD THROUGH THE END OF THE FORECAST PERIOD. THE RESULTING CROSS-TRACK SPREAD INCREASES TO NEARLY 400NM BY TAU 120. THE JTWC FORECAST IS CONSISTENT WITH THE ECMWF AND THE AI CONSENSUS THROUGH THE ENTIRE FORECAST. CONFIDENCE IS HIGH THROUGH TAU 72, THEN MEDIUM THROUGH TAU 120. INTENSITY GUIDANCE IS SPLIT BETWEEN THE SHIPS (BOTH GFS AND NAVGEM) AND COTC DEPICTING A PEAK INTENSITY AT TAU 72 OF 55 KNOTS AND THE HWRF, HAFS-A, CTCX AND FGNI ALL DEPICTING A PEAK AT TAU 72 BETWEEN 90-105 KNOTS. THE JTWC FORECAST IS PLACED NEAR THE SHIPS OUTPUT THROUGH TAU 36 AS IT DEPICTS A MUCH SHALLOWER AND MORE GRADUAL RATE OF INTENSIFICATION IN THE NEAR-TERM WHICH ALIGNS WITH THE CURRENT OBSERVATIONS. FROM TAU 48 ONWARDS THE JTWC FORECAST IS MORE CONSISTENT WITH THE HAFS-A MODEL DEPICTION. FORECAST CONFIDENCE IS MEDIUM TO TAU 72 AND LOW THEREAFTER. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN