WDXS31 PGTW 240300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 05S (DARIAN) WARNING 
NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.4S 83.3E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 713 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 36 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A RAGGED
EYE FEATURE, WHICH HAS SIGNIFICANTLY ERODED SINCE THE IMPRESSIVE
PEAK 12 HOURS AGO. THE CLOUD TOPS SURROUNDING THE EYE HAVE WARMED
TO -70 TO -78 CELSIUS, WHILE THE EYE TEMPERATURE HAS NOW TURNED
NEGATIVE AGAIN. A SERIES OF 91GHZ MICROWAVE IMAGERY SHOWED SIGNS OF
AN EYEWALL REPLACEMENT CYCLE (EWRC) BEGINNING AROUND THE 231800Z
HOUR, WITH THE GMI 89GHZ IMAGE AT THAT TIME SHOWING THE FIRST SIGNS
OF A SECONDARY EYEWALL, WHICH WAS MORE PRONOUNCED BY THE 232215Z
IMAGE AND BY THE 240015 SSMIS PASS, THE SECONDARY EYEWALL APPEARS
TO HAVE MERGED WITH THE INNER ONE. THE CIMSS M-PERC FORECAST
INDICATED A HIGH LIKELIHOOD OF AN EWRC AFTER THE 231200Z HOUR, WHICH
APPEARS TO HAVE BORN OUT. COMBINED WITH THE NOW QUASI-STATIONARY
MOTION RESULTING IN SIGNIFICANT UPWELLING OF COOLER WATERS, THE
SYSTEM HAS BEGUN TO RAPIDLY WEAKEN. THE INITIAL INTENSITY IS
LOWERED TO 115 KNOTS WITH MEDIUM CONFIDENCE, GENERALLY NEAR THE
AVERAGE BETWEEN THE AGENCY DATA-T NUMBERS AND CURRENT INTENSITY
ESTIMATES, SUPPORTED BY 110-115 KNOT ESTIMATES FROM ADT, OPEN-AIIR
AND A 232016Z AMSR2 WINDSPEED ESTIMATE OF 111 KNOTS. THE SYSTEM IS
NOW IN A WEAK STEERING ENVIRONMENT LEADING TO QUASI-STATIONARY
MOTION OF THE PAST SIX HOURS. CONDITIONS ARE GENERALLY FAVORABLE
WITH THE EXCEPTION OF THE LOCALIZED COOL SSTS.

INITIAL WIND RADII BASIS: AMSR2 WINDSPEED DATA

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN, SHIFTING TO THE
NEAR-EQUATORIAL RIDGE (NER) CENTERED FAR TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   KNES: T6.5 - 127 KTS
   FMEE: T6.0 - 115 KTS
   CIMSS SATCON: 134 KTS AT 231954Z
   CIMSS ADT: 112 KTS AT 240015Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: POLEWARD OUTFLOW CHANNEL INTO BASE OF 200MB TROF
TO THE SOUTHEAST.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 05S (DORIAN) HAS MOVED INTO A
COMPETING AND WEAK STEERING PATTERN, AS THE STR TO THE SOUTH
WEAKENS AND RETROGRADES TO THE WEST, ALLOWING FOR THE STRENGTHENING
NER TO THE NORTHEAST TO TAKE OVER AS THE DOMINANT STEERING
MECHANISM. THIS STEERING SHIFT WILL BE COMPLETE WITHIN THE NEXT 12
HOURS AND TC 05S WILL THEN BEGIN TO ACCELERATE TO THE SOUTHEAST.
BETWEEN TAUS 36 AND 60, THE NER WILL QUICKLY SLIDE TO THE WEST, TO
A POSITION SOUTH OF INDIA AND WEAKEN, WHILE THE STR TO THE
SOUTHWEST WILL MOVE EASTWARD AND STRENGTHEN. THIS WILL RESULT IN
ANOTHER PERIOD OF WEAK STEERING DURING THIS TIMEFRAME AS THE TWO
STEERING RIDGES COMPETE FOR DOMINANCE. BY TAU 72, THE STEERING
INFLUENCE WILL SHIFT OVER TO THE STR TO THE SOUTH, PUSHING TC 05S
ONTO A SOUTH-SOUTHWESTWARD TRACK THROUGH THE REMAINDER OF THE
FORECAST PERIOD. OVER THE PREVIOUS 12 HOURS TC 05S RAPIDLY
INTENSIFIED, BRIEFLY REACHING 130 KNOTS, BEFORE A COMBINATION OF AN
EWRC AND OCEANIC UPWELLING LED TO RAPID DECREASE IN INTENSITY. NOW
THAT THE SYSTEM HAS SLOWED TO A CRAWL OVER THE AREA OF MOST INTENSE
UPWELLING, THE SYSTEM WILL CONTINUE TO WEAKEN STEADILY THROUGH THE
NEXT 36 HOURS. AROUND TAU 36, THE SYSTEM WILL BACK MOVE OVER A WARM
TONGUE OF HIGHER OCEAN HEAT CONTENT, BUT AT THE SAME TIME WILL
EXPERIENCE SOME INCREASED SHEAR AND CONVERGENCE ALOFT DUE TO THE
DEVELOPMENT OF AN UPPER-LEVEL LOW TO THE WEST, RESULTING IN A
PERIOD OF STEADY INTENSITY THROUGH TAU 72. AFTER TAU 72, THE SYSTEM
WILL MORE RAPIDLY WEAKEN AS IT MOVES SOUTHWESTWARD OVER STEADILY
COOLER WATERS LESS THAN 26C, FORECAST TO WEAKEN TO JUST 45 KNOTS BY
THE END OF THE FORECAST PERIOD.  

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
GOOD AGREEMENT ON THE OVERALL TRACK, WITH THE JTWC TRACK FORECAST
LYING CLOSE TO THE MULTI-MODEL CONSENSUS MEAN, AND ROUGHLY IN THE
MIDDLE OF THE GUIDANCE ENVELOPE, WHICH GRADUALLY EXPANDS FROM 90NM
AT TAU 72 TO 180NM AT TAU 120. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT THROUGH THE FIRST 36 HOURS, BUT THEN DIVERGES RATHER
SIGNIFICANTLY. WITH THE BULK OF THE MODELS, WITH THE EXCEPTION OF
HWRF, SHOWING A VERY RAPID WEAKENING THROUGH THE FORECAST PERIOD.
THE GFS DECAY-SHIPS EVEN DISSIPATES THE SYSTEM BY TAU 72. THE
COUPLED HWRF MODEL HOWEVER CAPTURES THE MOVEMENT BACK OVER THE WARM
TONGUE THAT THE OTHER MODELS ARE NOT PICKING UP ON, AND SHOWS A
FLATTENING OF THE INTENSITY CURVE BETWEEN TAU 36 AND TAU 72. THE
JTWC FORECAST CLOSELY TRACKS THE HWRF, PARTICULARLY AFTER TAU 36. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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