WDXS31 PGTW 050900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 29S (INDUSA) WARNING 
NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.6S 70.4E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 847 NM SOUTHEAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 19 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY
DECOUPLING VORTEX, WITH DEEP CONVECTION BEING SHEARED OFF TO THE
SOUTHEAST AND THE LOW-LEVEL VORTEX BECOMING INCREASINGLY EXPOSED.
ANIMATED WATER VAPOR IMAGERY AND HIGH-RESOLUTION MODEL
CROSS-SECTIONS DEPICT A DEEP LAYER OF DRY AIR RAPIDLY MOVING IN
FROM THE NORTHWEST, ALONG THE SHEAR VECTOR, HELPING TO SMOTHER WHAT
REMAINS OF THE LOW LEVEL CIRCULATION CENTER (LLCC) AFTER THE HIGH
SHEAR ALREADY DECAPITATED THE VORTEX. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC
IN THE ANIMATED MSI. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE, BIASED HIGH IN LIGHT OF THE PGTW DVORAK CURRENT
INTENSITY ESTIMATE AND CONSISTENT WITH AN EARLIER SAR PASS WHICH
REVEALED A HIGHER WIND SPEED THAN ESTIMATED BY THE DVORAK-BASED
TECHNIQUES. ENVIRONMENTAL CONDITIONS HAVE RAPIDLY DETERIORATED AND
ARE CURRENTLY HIGHLY UNFAVORABLE, WITH VERY HIGH NORTHWESTERLY WIND
SHEAR (EXCEEDING 30 KNOTS), RAPIDLY COOLING SSTS (DOWN TO 24-25C),
AND RAPID DRY AIR ENTRAINMENT, OVERWHELMING THE ROBUST POLEWARD
OUTFLOW WHICH IS STILL IN PLACE.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   FMEE: T4.0 - 65 KTS
   FIMP: T4.0 - 65 KTS
   CIMSS ADT: 53 KTS AT 050600Z
   CIMSS AIDT: 49 KTS AT 050600Z
   CIMSS D-PRINT: 43 KTS AT 050600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 30+ KTS
   SST: 24-25 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY MID-LEVEL AIR FLOWING IN FROM THE NORTHWEST. 

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: HAVING ROUNDED THE STR AXIS YESTERDAY,
TROPICAL CYCLONE (TC) 29S (INDUSA) HAS TRACED A GRADUAL ARC TOWARDS
THE SOUTH-SOUTHEAST OVER THE COURSE OF THE PAST 24 HOURS. NOW
POSITIONED ON THE SOUTHWESTERN FLANK OF THE STR, AND WITHIN THE
TIGHTENING GRADIENT AHEAD OF AN EXTREMELY STRONG AND DEEP
UPPER-LEVEL TROUGH TO THE WEST, TC 29S WILL ACCELERATE
SOUTHEASTWARD THROUGH THE SHORT FORECAST PERIOD. REGARDING
INTENSITY, NOW THAT THE VORTEX IS DECOUPLED, BEING SMOTHERED BY DRY
MID-LEVEL AIR ALOFT AND MOVING OVER PROGRESSIVELY COOLER WATERS, IT
WILL STEADILY WEAKEN THROUGH THE FORECAST PERIOD. AT THE SAME TIME,
THE SYSTEM HAS ALREADY BEGUN THE EARLY PHASES OF EXTRA-TROPICAL
TRANSITION (ETT) AND IS FORECAST TO COMPLETE ETT WITHIN THE NEXT 24
HOURS AS IT MOVES UNDER AN UPPER-LEVEL JET STREAK AND UNDERGOES
FRONTOGENESIS.   

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE GUIDANCE IS IN STRONG
AGREEMENT ON THE FORECAST TRACK, WITH ALL AVAILABLE CONSENSUS
MEMBERS CONFINED TO A NARROW TRACK ENVELOPE OF JUST 50NM, LENDING
HIGH CONFIDENCE TO THE JTWC FORECAST TRACK. INTENSITY GUIDANCE IS
ALSO IN GOOD AGREEMENT, WITH ALL MEMBERS INDICATED STEADY TO RAPID
WEAKENING. WHILE THE DECAY-SHIPS IS LIKELY A BIT TOO FAST IN
DISSIPATING TC 29S, THE HAFS-A, HWRF AND COAMPS-TC ARE IN GOOD
AGREEMENT IN A SLOWER BUT MORE STEADY WEAKENING AND THE JTWC
FORECAST IS PLACED NEAR THESE MODELS WITH HIGH CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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