WDXS31 PGTW 162100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (DJOUNGOU) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.2S 66.6E INITIAL INTENSITY: 65 KTS GEOGRAPHIC REFERENCE: 647 NM SOUTH-SOUTHWEST OF DIEGO GARCIA MOVEMENT PAST 6 HOURS: EASTWARD AT 05 KTS SIGNIFICANT WAVE HEIGHT: 23 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL CYCLONE (TC) 13S (DJOUNGOU) CONTINUES TO STEADILY CONSOLIDATE AND INTENSIFY AS IT TRACKS SLOWLY EASTWARD. THE LATEST ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT INNER CORE OF CONVECTION WHICH HAS OVER THE PAST FEW HOURS RAPIDLY DEVELOPED INTO A SMALL CENTRAL DENSE OVERCAST (CDO), WITH OVERSHOOTING TOPS APPROACHING -90C. A 161637Z GMI COLOR ENHANCED 37GHZ MICROWAVE IMAGE DEPICTED A WELL-DEFINED MICROWAVE EYE FEATURE, SURROUNDED BY A CYAN RING, AND FRAGMENTED SPIRAL BANDS OF CONVECTION WRAPPING INTO THE INNER CORE. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON AN EXTRAPOLATION OF THE MICROWAVE EYE SUPPORTED BY A WARM SPOT IN THE GOES-IO BD-ENHANCED IMAGE FROM 161745Z. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A T4.0 CURRENT INTENSITY ESTIMATE FROM KNES AND A DVORAK DATA-T ESTIMATE OF T4.0 FROM PGTW. ANALYSIS REVEALS A VERY FAVORABLE ENVIRONMENT WITH LOW (0-5 KNOTS) WEST-NORTHWEST SHEAR, WARM SSTS, RELATIVELY HIGH, OHC AND GOOD RADIAL OUTFLOW ENHANCED BY A ROBUST POLEWARD OUTFLOW CHANNEL INTO THE DIVERGENT QUADRANT OF A 120 KNOT JET MAX TO THE SOUTHEAST. WHILE OVERALL SHEAR IS QUITE LOW, MID-LEVEL SHEAR IS SLIGHTLY HIGHER BASED ON GFS MODEL SOUNDINGS AND THE PRESENCE OF A SHARP UPSHEAR EDGE OF THE MID-LEVEL CLOUD DECK. OVER THE PAST 12 HOURS, THE SYSTEM HAS TAKEN A SLOWER, MORE EASTWARD TRACK THAN ANTICIPATED, LIKELY IN RESPONSE TO THE ORIENTATION OF THE LOW- TO MID-LEVEL RIDGE TO THE NORTH. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER NEAR EQUATORIAL RIDGE (NER) TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS KNES: T4.0 - 65 KTS FMEE: T3.5 - 55 KTS FIMP: T3.5 - 55 KTS CIMSS ADT: 55 KTS AT 161500Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 0-5 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THE PHASE TRANSITION TYPE HAS BEEN CHANGED FROM EXTRATROPICAL TO SUBTROPICAL AND THE FORECAST HAS BEEN TRUNCATED TO 96 HOURS. FORECAST DISCUSSION: TC 13S IS FORECAST TO CONTINUE TRACKING GENERALLY EAST-SOUTHEASTWARD OVER THE NEXT 12 TO 24 HOURS AS IT CONTINUES TO STRENGTHEN AND INTENSIFY. AS THE VORTEX EXPANDS, THE STEERING LEVEL WILL GET STEADILY HIGHER, LEADING TO A MORE SOUTHEASTWARD TRACK AFTER TAU 24. THE TIGHT GRADIENT BETWEEN THE NER TO THE NORTH AND A STRONG MID-LATITUDE TROUGH TO THE SOUTH AND WEST WILL ACCELERATE TC 13S UP TO ABOUT 20 KNOTS BY TAU 72 BEFORE SLOWING ONCE MORE BY THE END OF THE FORECAST AS IT RUNS INTO A LOW- TO MID-LEVEL RIDGE LURKING OFF THE WEST COAST OF AUSTRALIA. IN TERMS OF INTENSITY, THE ENVIRONMENT IS PRIMED FOR RAPID INTENSIFICATION (RI), WITH HIGHLY FAVORABLE ENVIRONMENTAL PARAMETERS LINING UP SUPPORT. THE ONLY THING HOLDING THE SYSTEM BACK AT THE MOMENT IS A BIT OF MID-LEVEL SHEAR, BUT AVAILABLE GUIDANCE SUGGESTS THIS SHOULD WEAKEN IN THE NEXT 6-12 HOURS. ONCE THE CONVECTION CAN BEGIN TO WRAP UPSHEAR, THE SYSTEM WILL EMBARK UPON A PERIOD OF RI, WITH THE FORECAST CALLING FOR A PEAK OF 115 KNOTS BY TAU 36. BUT THE WINDOW FOR RI IS BRIEF AS SHEAR WILL SHARPLY INCREASE BEGINNING AT TAU 48, INCREASING FURTHER TO NEAR 60 KNOTS BY TAU 72 BRINGING WITH IT A SURGE IN VERY DRY MID-LEVEL AIR. THE HIGH VWS AND LOW MOISTURE CONTENT WILL CONSPIRE TO DECAPITATE AND SMOTHER TC 13S BEGINNING AS EARLY AS TAU 48. AS THE SYSTEM IS EXPECTED TO RETAIN ITS WARM CORE CHARACTERISTICS AND REMAIN OVER MARGINAL (25-26C) WATERS DURING THIS TIME, IT IS FORECAST TO UNDERGO SUBTROPICAL TRANSITION (STT) BEGINNING BY TAU 72 AND POTENTIALLY AS EARLY AS TAU 60. TRANSITION TO A STORM-STRENGTH SUBTROPICAL LOW IS ANTICIPATED NO LATER THAN TAU 96. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN VERY GOOD AGREEMENT IN THE OVERALL TRACK DIRECTION, AS TO BE EXPECTED WITH SUCH A WELL-STRUCTURED STEERING PATTERN. CROSS-TRACK SPREAD AT TAU 72 IS JUST 150NM BETWEEN THE EGRR, GALWEM AND UKMET ENSEMBLE MARKING THE NORTHERN EDGE AND THE NAVGEM MARKING THE SOUTHERN EDGE OF THE GROUPING. THROUGH THE END OF THE FORECAST, THE MODELS REMAIN IN GOOD CROSS-TRACK AGREEMENT, BUT BEGIN TO SPREAD OUT ALONG-TRACK, REACHING UP TO 410NM BETWEEN THE GALWEM AND UKMET ENSEMBLE BY TAU 96. THE JTWC FORECAST IS CONSISTENT WITH THE CONSENSUS MEAN THROUGHOUT THE FORECAST PERIOD WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM WILL INTENSIFY FOR THE NEXT 36 HOURS, THE ONLY QUESTION IS BY HOW MUCH. THE SHIPS (GFS) IS THE MOST BEARISH, PEAKING THE SYSTEM AT JUST 85 KNOTS, WHILE THE HAFS-A IS THE MOST BULLISH REACHING 135 KNOTS. THE COAMPS-TC, HAFS-A, AND HWRF ALL PEAK THE SYSTEM BETWEEN 115-135 KNOTS. ADDITIONALLY, MULTIPLE RI AIDS ARE TRIGGERED WITH THIS RUN, PROVIDING ADDITIONAL CONFIDENCE TO THE JTWC FORECAST OF RI OF 50 KNOTS IN 36 HOURS. AFTER THE SHORT RUN TO THE PEAK, THE SYSTEM WILL RAPIDLY WEAKEN THROUGH THE REMAINDER OF THE FORECAST AS IT UNDERGOES STT. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN