WDXS31 PGTW 182100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (DJOUNGOU) WARNING NR 007// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 21.6S 81.0E INITIAL INTENSITY: 120 KTS GEOGRAPHIC REFERENCE: 1000 NM SOUTH-SOUTHEAST OF DIEGO GARCIA MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 29 KTS SIGNIFICANT WAVE HEIGHT: 56 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL CYCLONE (TC) 13S (DJOUNGOU) IS NOW RAPIDLY DETERIORATING AFTER PEAKING ABOUT EIGHT HOURS AGO. REANALYSIS OF THE ADVANCED DVORAK TECHNIQUE (ADT) RAW DATA OUTPUTS WHICH REACHED AS HIGH AS T6.8, THE SYSTEM APPEARS TO HAVE PEAKED BETWEEN 180900Z AND 181000Z, BETWEEN 130 AND 135 KNOTS. SINCE THAT TIME, THE EYE HAS QUICKLY FILLED IN AND IS NO LONGER APPARENT IN THE ANIMATED ENHANCED INFRARED (EIR) IMAGERY. THE CLOUD TOPS REMAIN FAIRLY COLD IN THE EIR AND AN 181628Z AMSU-B 89GHZ MICROWAVE IMAGE REVEALED A WELL- DEFINED UPPER-LEVEL MICROWAVE EYE FEATURE. THE IMPACT OF NORTHWESTERLY SHEAR WAS ALREADY EVIDENT IN MICROWAVE IMAGERY FROM 181304Z, WHICH SHOWED A PRONOUNCED TILT BETWEEN THE 36GHZ AND 89GHZ EYE FEATURES. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE TIGHT GROUPING OF THE AGENCY FIXES, WHICH WERE PLACED USING THE LAST COUPLE OF FRAMES WITH AN EVIDENT EYE FEATURE, AND EXTRAPOLATION OF THE AMSU-B MICROWAVE EYE FEATURE NOTED ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON AN AVERAGE OF THE SUBJECTIVE AND OBJECTIVE FIXES NOTED BELOW. ANALYSIS SHOWS THAT THE SYSTEM HAS MOVED INTO AN ENVIRONMENT WHICH HAS VERY RAPIDLY SHIFTED FROM FAVORABLE TO HIGHLY UNFAVORABLE, WITH HIGH VWS BEING THE PRIMARY NEGATIVE FACTOR. SSTS REMAIN WARM AND UPPER-LEVEL OUTFLOW CONTINUES TO BE EXTREMELY STRONG POLEWARD, INTO THE BASE OF A 130 KNOT JET MAX TO THE SOUTHEAST. THE SYSTEM IS RACING SOUTHEASTWARD AT ALMOST 30 KNOTS IN THE TIGHT GRADIENT FLOW BETWEEN A STR TO THE EAST AND A MAJOR SHORTWAVE TROUGH TO THE WEST. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: TIGHT GRADIENT BETWEEN A STRONG STR CENTERED OVER WESTERN AUSTRALIA AND A DEEP, MAJOR SHORTWAVE TROUGH TO THE WEST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.5 - 127 KTS KNES: T6.5 - 127 KTS DEMS: T6.5 - 127 KTS FMEE: T6.5 - 127 KTS FIMP: T5.5 - 102 KTS CIMSS SATCON: 125 KTS AT 181307Z CIMSS ADT: 124 KTS AT 181800Z CIMSS AIDT: 116 KTS AT 181800Z CIMSS DPRINT: 117 KTS AT 181800Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE VWS: 30+ KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: VERY DRY AIR BEGINNING TO WRAP UP THE WEST AND NORTH OF THE LLCC. 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 TRACK FROM THE PREVIOUS WARNING, OTHER THAN A TRUNCATION TO 48 HOURS. HOWEVER, THE FINAL PHASE TRANSITION HAS BEEN CHANGED TO EXTRATROPICAL WITH THIS FORECAST. FORECAST DISCUSSION: AFTER PEAKING AT OR SLIGHTLY ABOVE 130 KNOTS ABOUT EIGHT HOURS AGO, TC 13S HAS STARTED TO RAPIDLY WEAKEN AS IT SUCCUMBS TO PERSISTENT AND INCREASING NORTHWESTERLY SHEAR AND BEGINS TO FEEL THE EFFECTS OF SIGNIFICANT INTRUSIONS OF DRY AIR. THE STEERING INFLUENCE IS QUITE STRAIGHT FORWARD, AND WILL DRIVE THE SYSTEM TOWARDS THE SOUTHEAST AT A STEADY 30 KNOTS FOR THE NEXT 24 TO 36 HOURS. A SLIGHT SLOW DOWN AND SHIFT TO AN EASTWARD TRACK IS EXPECTED BY THE END OF THE FORECAST AS THE STEERING LEVEL SHIFTS LOWER IN THE ATMOSPHERE, WHERE THE STEERING GRADIENT WILL BE WEAKER. WITH THE SHEAR HAVING NOW SUCCESSFULLY PENETRATED TO THE INNER CORE OF THE SYSTEM, IT WILL NOT BE LONG BEFORE THE VORTEX IS COMPLETELY TORN ASUNDER. IN FACT THE DECAPITATION INDEX (DCAP) MODEL SUGGESTS THIS PROCESS WILL BE COMPLETE WITHIN THE NEXT 12 TO 24 HOURS. AT THE SAME TIME, BOTH THE HAFS-A AND HWRF MODEL CROSS- SECTIONS SHOW THE PROCESS VERY WELL, WITH ALL THAT REMAINS OF THE LOW- LEVEL VORTEX DRIVING SOUTHEASTWARD BY TAU 36, COMPLETELY SMOTHERED BY A DEEP LAYER OF VERY DRY AIR EXTENDING FROM 800MB ALL THE WAY UP TO 300MB. THE SYSTEM WILL BEGIN SUBTROPICAL TRANSITION (STT) SHORTLY BUT THIS PHASE OF ITS LIFE WILL BE SHORT-LIVED, AND IT WILL NEVER ACTUALLY COMPLETE STT. INSTEAD, THE SYSTEM QUICKLY SHIFTS TO AN EXTRATROPICAL TRANSITION (ETT) AS IT MOVES INTO THE LEFT ENTRANCE REGION OF A 150 KNOT JET MAX AND EMBEDS ALONG A TIGHT THERMAL GRADIENT AND DEVELOPS FRONTAL CHARACTERISTICS. ETT WILL BE COMPLETE NO LATER THAN TAU 48 AND COULD POTENTIALLY WRAP UP 12 HOURS EARLIER. MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY TIGHT AGREEMENT, WITH MINIMAL CROSS AND ALONG-TRACK SPREAD THROUGH THE SHORT DURATION OF THE FORECAST PERIOD. THE JTWC FORECAST LIES CLOSE TO THE CONSENSUS MEAN WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, WITH ALL OF THE GUIDANCE SHOWING A SHARP AND RAPID WEAKENING THROUGH THE DURATION OF THE FORECAST. THE JTWC FORECAST LIES ON THE HIGHER END OF THE ENVELOPE WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: MEDIUM// NNNN