WDXS31 PGTW 250300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 05S (DARIAN) WARNING 
NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.5S 84.7E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 845 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 34 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
OVER THE PAST 12 HOURS, TROPICAL CYCLONE 05S (DARIAN) HAS WEAKENED
FAIRLY SIGNIFICANTLY, AS IT DRIFTED SLOWLY TOWARDS THE SOUTHEAST
OVER AN AREA OF STRONG OCEANIC UPWELLING. OVER THE PAST SIX HOURS,
THE SYSTEM HAS LOST ITS PREVIOUSLY WELL-DEFINED EYE IN THE ENHANCED
INFRARED (EIR) IMAGERY, THOUGH A STRONG MICROWAVE EYE FEATURE
REMAINS PRESENT IN THE MOST RECENT SSMIS 89GHZ IMAGE FROM 250016Z.
DEEP CONVECTION HAS STARTED TO REDEVELOP OVER THE PAST COUPLE OF
HOURS, WITH COLD CLOUD TOPS APPROACHING -80C DEVELOPING NEAR THE
ASSESSED CENTER. THE MICROWAVE IMAGERY INDICATES THE EYEWALL IS
OPEN ON THE NORTHEAST SIDE, AND HIGH-RESOLUTION MODEL FIELDS
SUGGEST THE PRESENCE OF A WEDGE OF DRY AIR IN THE NORTHEAST SECTOR
WHICH WHEN COMBINED WITH THE MUCH COOLER SSTS TO THE NORTH, WOULD
SUPPORT A WEAKER WIND FIELD ON THAT SIDE OF THE SYSTEM. THE INITIAL
POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN
EXTRAPOLATION OF THE MICROWAVE EYE IN THE SSMIS IMAGERY. THE
INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN
AVERAGE OF AVAILABLE AGENCY DVORAK CURRENT INTENSITY ESTIMATES
RANGE BETWEEN T5.0 TO T5.5, AND ADT AND AIDT ESTIMATES OF 90 KTS
AND 89 KTS RESPECTIVELY. THE OVERALL ENVIRONMENT IS FAVORABLE, WITH
THE SYSTEM NOW MOVING AWAY FROM THE UPWELLING AND INTO A WARM SST
TONGUE. IN THE UPPER-LEVELS, SHEAR IS MODERATE AND OUTFLOW IS
RESTRICTED ON TO A POLEWARD CHANNEL ONLY, NOW THAT A WEAK
UPPER-LEVEL LOW HAS DEVELOPED JUST TO THE WEST OF THE SYSTEM,
CUTTING OFF THE WESTWARD AND EQUATORWARD OUTFLOW THAT WAS PRESENT
YESTERDAY. TC 05S IS MOVING SOUTHEASTWARD ALONG THE SOUTHWESTERN
SIDE OF A NEAR-EQUATORIAL RIDGE (NER).

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTH-SOUTHWEST PERIPHERY OF A
DEEP-LAYER NEAR EQUATORIAL RIDGE (NER) CENTERED SOUTHWEST OF
SUMATRA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   KNES: T5.0 - 90 KTS
   FMEE: T5.0 - 90 KTS
   CIMSS SATCON: 105 KTS AT 241935Z
   CIMSS ADT: 90 KTS AT 250015Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: THROUGH THE FIRST 12 HOURS OF THE FORECAST, TC
05S WILL CONTINUE TO TRACK SOUTHEASTWARD AT A FAIR CLIP, ALONG THE
STRONG STEERING GRADIENT ON THE SOUTHWEST SIDE OF THE NER. BY TAU
24, TC 05S WILL SLAM ON THE BRAKES AS THE NER QUICKLY MOVES WEST
AND WEAKENS, PUTTING TC 05S INTO A WEAK STEERING ENVIRONMENT. THE
SYSTEM WILL SLOWLY TURN TO THE SOUTH THEN SOUTHWEST THROUGH TAU 48
AS THE STEERING PATTERN SHIFTS TO THE BUILDING SUBTROPICAL RIDGE
(STR) TO THE SOUTH. AFTER TAU 48 THE SYSTEM WILL ACCELERATE
SOUTHWESTWARD THROUGH TAU 96. BY TAU 120 THE STR WILL SHIFT TO THE
NORTH AND TAKE UP POSITION TO THE EAST OF TC 05S, WHICH WILL LEAD
THE SYSTEM TO BEGIN A POLEWARD TURN BY THE END OF THE FORECAST
PERIOD. OVER THE NEXT 24 HOURS THE SYSTEM WILL CONTINUE TO SLOWLY
WEAKEN DUE TO NORTHERLY SHEAR AND INTRUSION OF DRY MID-LEVEL AIR
FROM THE NORTH. THE WEAKENING TREND IS FORECAST TO BE ARRESTED
AFTER TAU 24 AS THE SYSTEM MOVES OVER THE WARMEST PORTION OF THE
WARM SST TONGUE AND SHEAR RELAXES SOMEWHAT. BUT THE ARRESTED
WEAKENING WILL BE SHORT-LIVED, AND AFTER TAU 48 THE SYSTEM WILL
BEGIN TO RAPIDLY WEAKEN AS IT MOVES INTO STEADILY COOLER WATERS AS
IT CONTINUES MOVING SOUTHWESTWARD. BY TAU 96 OR SLIGHTLY EARLIER,
THE SYSTEM WILL BE OVER WATERS BETWEEN 24-25C, WILL BE MOVING
POLEWARD OF THE SUBTROPICAL RIDGE, AND WILL BE INCREASINGLY
ENGULFED BY A DRY AIR MASS, MARKING THE START OF SUBTROPICAL
TRANSITION. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
VERY GOOD AGREEMENT THROUGH THE DURATION OF THE FORECAST, BOTH IN
TERMS OF CROSS AND ALONG-TRACK SPREAD. THE JTWC FORECAST LIES NEAR
THE MULTI-MODEL CONSENSUS THROUGH TAU 36, THEN JUST NORTH OF THE
MEAN THROUGH THE REMAINDER OF THE FORECAST PERIOD, WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE IS IN FAIR AGREEMENT THROUGH THE
FORECAST PERIOD. IN THE FIRST 24 HOURS, THE COAMPS-TC CONTINUES TO
INDICATE INTENSIFICATION, WHILE THE REMAINDER OF THE GUIDANCE
PACKAGE INDICATES VARIOUS AMOUNTS OF WEAKENING, WITH THE HWRF BEING
THE MOST SHOWING THE MOST AGGRESSIVE WEAKENING. THE GFS AND HWRF
SHOW THE ARRESTED WEAKENING PHASE BETWEEN TAU 24 AND 36 VERY WELL,
AND THEN REJOIN THE PACK WITH RAPID WEAKENING AFTER TAU 36. THE
GUIDANCE IS SPREAD ACROSS A 20 KNOT ENVELOPE BETWEEN 35-55 KNOTS AT
TAU 120. THE JTWC FORECAST LIES ABOVE THE CONSENSUS MEAN THROUGH
THE FORECAST PERIOD, AND MOST CLOSELY TRACKS THE GFS SOLUTION WITH
MEDIUM CONFIDENCE. 

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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