WDXS31 PGTW 260300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 05S (DARIAN) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.5S 85.2E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 934 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 34 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE DARIAN (05S) IS ONCE MORE PROVING TO BE
EXCEPTIONALLY STUBBORN AND HAS RAPIDLY INTENSIFIED FOR A THIRD TIME
IN ITS LIFE CYCLE, FROM A LOW OF 80 KNOTS AT 251200Z TO 110 KNOTS
JUST 12 HOURS LATER.  ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS A RAGGED, 25NM EYE FEATURE WHICH APPEARS TO HAVE
PEAKED AT THE 260000Z HOUR WITH AN EYE TEMPERATURE THAT GOT UP TO
ABOUT -10C, SURROUNDED BY COLD TOPS BETWEEN -72C TO -82C. A 252006Z
AMSR2 89GHZ MICROWAVE IMAGE SHOWED A NEARLY COMPLETE EYEWALL WITH
THE WEAKEST POINT ON THE NORTHEAST SIDE, WHILE A 252206Z SSMIS
91GHZ IMAGE SHOWED A VERY WEAK NORTHEAST EYEWALL. SHEAR APPEARS TO
HAVE BACKED OF A COUPLE OF KNOTS (CLOSER TO 15 KTS THAN 20 KTS) AND
THE SYSTEM HAS BECOME MORE VERTICALLY STACKED OVER THE PAST 12
HOURS AND PUSHED AWAY THE DRY AIR THAT WAS PREVIOUSLY INTRUDING IN
FROM THE NORTH. SSTS HAVE WARMED ANOTHER DEGREE OR SO AND ARE
CURRENTLY ESTIMATED TO BE 27-28C. THE COMBINATION OF THESE FACTORS
HAS ALLOWED FOR THE LATEST ROUND OF RAPID INTENSIFICATION (RI).
THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON AN
EXTRAPOLATION OF THE MICROWAVE EYE FEATURES. THE INITIAL INTENSITY
IS ASSESSED WITH HIGH CONFIDENCE USING A BLEND OF ALL AVAILABLE
INTENSITY ESTIMATES INCLUDING OBJECTIVE DVORAK ESTIMATES BETWEEN
T5.0 TO T6.0, ADT OF T5.6, AIDT OF 104 KTS, DMN OF 103 KTS,
OPEN-AIIR OF 106 KTS AND A SATCON OF 110 KNOTS. THE SYSTEM HAS
SLOWED SIGNIFICANTLY AS IT HAS MOVED INTO A WEAK STEERING PATTERN
WITH THE NEAR EQUATORIAL RIDGE (NER) AND SUBTROPICAL RIDGE (STR)
COMPETING FOR STEERING.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK AND AMSR2 WIND DATA.

CURRENT STEERING MECHANISM: WEAK AND COMPETING STEERING PATTERN
BETWEEN THE NER TO THE NORTH AND STR TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T5.5 - 102 KTS
   KNES: T6.0 - 115 KTS
   FMEE: T5.5 - 102 KTS
   CIMSS SATCON: 110 KTS AT 252006Z
   CIMSS ADT: 107 KTS AT 260015Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: LOCALIZED RADIAL OUTFLOW WITH A MODERATE POLEWARD
CHANNEL.

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: TC 05S HAS SLOWED SIGNIFICANTLY AS IT HAS
MOVED INTO A WEAK STEERING ENVIRONMENT, WITH THE STR TO THE SOUTH
AND NER TO THE NORTH COMPETING FOR STEERING DOMINANCE. GLOBAL
MODELS SUGGEST THAT THE STR TO THE SOUTH WILL STRENGTHEN AND MOVE
TO THE EAST AND INDUCE TC 05S TO TURN SOUTHWESTWARD BY TAU 24. THE
SOUTHWESTWARD MOTION IS EXPECTED TO CONTINUE THROUGH THE DURATION
OF THE FORECAST PERIOD, WITH A SLIGHTLY MORE POLEWARD TRACK BY TAU
120 AS THE SYSTEM BEGINS TO ROUND THE RIDGE AXIS. IN TERMS OF
INTENSITY, TC 05S HAS ONCE AGAIN EXCEEDED EXPECTATION AND PROVEN TO
BE RESILIENT TO THE MODERATE NORTHERLY SHEAR AND DRY AIR INTRUSION.
WHILE THE NORTHERLY PRESSURE IS STILL PRESENT, SHEAR VALUES HAVE
DROPPED A NOTCH OR TWO, ALLOWING FOR THE CORE TO BECOME MORE
VERTICALLY STACKED AND SHOULDER THE DRY AIR FURTHER AWAY FROM THE
CORE. COUPLED WITH MOVEMENT OVER A WARM TONGUE OF 27-28C WATERS,
THE SYSTEM HAS BEEN ABLE TO INTENSIFY. HOWEVER, THIS
INTENSIFICATION WILL BE SHORT-LIVED, AS TC 05S WILL MOVE INTO
PROGRESSIVELY COOLER WATERS FROM THIS POINT FORWARD. SHEAR IS ALSO
EXPECTED TO INCREASE, LEADING TO A PRONOUNCED VORTEX TILT AND
ALLOWING FOR A RENEWED INFLUX OF DRY AIR FROM THE NORTH BEGINNING
AROUND TAU 24. THIS TREND WILL ACCELERATE AFTER TAU 24, LEADING TO
RAPID WEAKENING DOWN TO 45 KNOTS BY TAU 72. THROUGH THE REMAINDER
OF THE FORECAST THE SYSTEM WILL LINGER AROUND 40 KNOTS AS IT GLIDES
SOUTHWEST THROUGH RELATIVELY COOLER WATERS AROUND 25C AND
TRANSITIONS TO A SUBTROPICAL CYCLONE. TRANSITION TO A GALE-FORCE
SUBTROPICAL LOW IS EXPECTED TO BE COMPLETE NO LATER THAN TAU 120,
AND POTENTIALLY AS EARLY AS TAU 96, FAR TO THE SOUTHEAST OF
MAURITIUS.

MODEL DISCUSSION: DYNAMIC AND ENSEMBLE TRACK GUIDANCE IS IN VERY
GOOD AGREEMENT, WITH MINIMAL CROSS OR ALONG-TRACK SPREAD, THROUGH
THE DURATION OF THE FORECAST PERIOD, LENDING HIGH CONFIDENCE TO THE
JTWC FORECAST TRACK, WHICH LIES NEAR THE CONSENSUS MEAN. INTENSITY
GUIDANCE IS ALSO IN RELATIVELY GOOD AGREEMENT WITH THE BULK OF THE
MEMBERS SUPPORTING THE JTWC FORECAST WILL MEDIUM CONFIDENCE, THOUGH
HWRF AND MESOSCALE GFS INDICATE A MUCH FASTER RATE OF WEAKENING
THROUGH THE FIRST 24 HOURS.

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