WDXS31 PGTW 220900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 05S (DARIAN) WARNING 
NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.0S 87.4E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 948 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 42 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A DEGRADING
INNER CORE STRUCTURE, WITH THE EYE FILLING WITH CLOUD AND THE
EYEWALL BECOMING LESS WELL-DEFINED IN INFRARED IMAGERY DURING THE
PAST 12 HOURS. A 220547Z GMI MICROWAVE PASS SUGGESTS THAT THE
EYEWALL IS STILL CLOSED, BUT WEAK IN THE SOUTHEAST QUADRANT.
EARLIER MICROWAVE DATA SHOWED AN OPEN EYEWALL AT TIMES. AGENCY
DVORAK INTENSITY ESTIMATES HAVE DECLINED ACCORDINGLY, WITH DATA-T
NUMBERS OF 5.5 FROM PGTW AND FMEE, AND 5.0 FROM KNES. THE INITIAL
INTENSITY IS THUS DECREASED TO 115 KT. WATER VAPOR CHANNELS SHOW
DRY AIR CLOSE BY TO THE EAST OF THE CYCLONE, AND MODELED VERTICAL
PROFILES FROM THE GFS AND ECMWF SHOW 20-25 KT OF MID-LEVEL WIND
SHEAR OUT OF THE EAST, POTENTIALLY CAUSING INGESTION OF THIS DRY
AIR MASS AND CONTRIBUTING TO THE OBSERVED DEGRADATION OF THE CORE
STRUCTURE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   CIMSS SATCON: 109 KTS AT 220203Z
   CIMSS ADT: 112 KTS AT 220315Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL CYCLONE 05S (DARIAN) IS ON A
WEAKENING TREND, POTENTIALLY DUE TO MID-LEVEL EASTERLY WIND SHEAR
AND UPWELLING OF COOLER WATER AS THE CYCLONE MOVES AT A SPEED OF 8
KT IN AN AREA OF RELATIVELY LOW OCEAN HEAT CONTENT. A MID-LEVEL
RIDGE TO THE SOUTH IS CURRENTLY STEERING DARIAN GENERALLY WESTWARD,
KEEPING IT OVER 26-27 DEGREE CELSIUS WATER DURING THE NEXT 36-48
HOURS. THEREAFTER, A DIGGING LONGWAVE TROUGH WEST OF AUSTRALIA IS
EXPECTED TO INDUCE A TURN TOWARDS THE SOUTH AND SOUTHEAST, LIKELY
RESULTING IN A SLOWING OF DARIAN'S FORWARD MOTION FOR A TIME. THE
COUPLED HWRF MODEL SUGGESTS THAT THIS SLOW TURN COULD INDUCE MORE
OCEANIC UPWELLING, CONTRIBUTING TO CONTINUING WEAKENING OF THE
STORM, EVEN THOUGH WIND SHEAR IS EXPECTED TO ABATE AFTER 24 HOURS.
THE SUITE OF DYNAMICAL AND STATISTICAL MODEL GUIDANCE GENERALLY
AGREES, SHOWING WEAKENING THROUGHOUT THE FORECAST PERIOD. DARIAN'S
SOUTHWARD TURN WILL TAKE IT OVER WATERS COOLER THAN 26 DEGREES
CELSIUS TOWARDS THE END OF THE FORECAST PERIOD, AND THE JTWC
INTENSITY FORECAST DECREASES TO 60 KT BY 120 HOURS. DURING THE
96-120 HOUR PERIOD, THE AFOREMENTIONED LONGWAVE TROUGH WEST OF
AUSTRALIA WILL PULL AWAY, ALLOWING A RIDGE TO REBUILD SOUTH OF
DARIAN ONCE AGAIN, TURNING THE CYCLONE BACK SOUTHWESTWARD OR
WESTWARD NEAR THE END OF THE FORECAST.

MODEL DISCUSSION: CROSS-TRACK MODEL SPREAD IS ANOMALOUSLY HIGH DUE
TO UNCERTAINTY AROUND THE LONGITUDE AT WHICH DARIAN WILL TURN
SOUTHWARD. THE JTWC TRACK FORECAST STICKS CLOSE TO A BLEND OF THE
GFS, GFS ENSEMBLE MEAN, ECMWF, AND ECMWF ENSEMBLE MEAN, WHICH ARE
GENERALLY EAST OF THE MULTI-MODEL CONSENSUS. THE NAVGEM, GALWEM,
AND UKMET MODELS ARE WESTERN OUTLIERS RELATIVE TO THIS GROUP. THE
JTWC INTENSITY FORECAST STAYS SLIGHTLY ABOVE THE CONSENSUS FOR THE
FIRST 24-36 HOURS, THEN CLOSE TO THE CONSENSUS THEREAFTER.

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