WDXS31 PGTW 040900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 29S (INDUSA) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.3S 70.2E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 726 NM EAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 36 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A SMALL,
CLOUD-COVERED EYE FEATURE, WHILE ENHANCED INFRARED (EIR) IMAGERY 
REVEALS A DISTINCT PINHOLE EYE DIAMETER MEASURED AT APPROXIMATELY 
10NM. BOTH MSI AND EIR, AUGMENTED BY A 040448Z AMSU-B 89GHZ MICROWAVE 
PASS, INDICATE A HIGHLY COMPACT INNER CORE AND MINIATURE CENTRAL 
DENSE OVERCAST (CDO), WITH CONVECTIVE FEEDER BANDS EXTENDING 
PERIPHERALLY, PARTICULARLY IN THE NORTHERN QUADRANT. ANIMATED WATER 
VAPOR IMAGERY AND CIMSS ATMOSPHERIC MOTION VECTORS (AMVS) INDICATE 
EXTREMELY VIGOROUS POLEWARD OUTFLOW CHANNELS SOUTHWARD IN ADVANCE OF 
A DEEP UPPER-LEVEL TROUGH APPROACHING FROM THE WEST. THE INITIAL 
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE IN 
THE GOES-IO EIR IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH LOW 
CONFIDENCE HOWEVER. AGENCY SUBJECTIVE DVORAK FIXES ARE CONSISTENT AT 
T4.5, HOWEVER THE OBJECTIVE TECHNIQUES (PRIMARILY ADT AND AIDT) ARE 
STRUGGLING TO RESOLVE THE PINHOLE EYE AND PROVIDING ESTIMATES FAR TOO 
LOW. THE INITIAL INTENSITY OF 90 KNOTS IS DERIVED FROM EXTRAPOLATION 
FROM EARLIER SAR PEAK VMAX DATA, A 0047Z D-MINT ESTIMATE OF 88 KNOTS 
AND AN OVERALL QUALITATIVE ASSESSMENT OF THE STRUCTURE OF THE SYSTEM 
IN THE EIR, PARTICULARLY THE BD-ENHANCEMENT. ENVIRONMENTAL CONDITIONS
ARE FAVORABLE, WITH LOW VERTICAL WIND SHEAR (VWS), WARM SSTS AND
ROBUST POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   DEMS: T4.5 - 77 KTS
   FMEE: T4.5 - 77 KTS
   FIMP: T4.5 - 77 KTS
   CIMSS ADT: 51 KTS AT 040600Z
   CIMSS AIDT: 56 KTS AT 040600Z
   CIMSS D-MINT: 88 KTS AT 040047Z
   CIMSS D-PRINT: 70 KTS AT 040530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN TRUNCATED TO 36
HOURS WITH EXTRATROPICAL TRANSITION. 

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 27S (INDUSA) HAS TRACKED
SOUTHWESTWARD OVER THE PAST 12 HOURS ALONG THE NORTHWESTERN FLANK
OF THE STR TO THE EAST. IT IS CURRENTLY APPROACHING THE RIDGE AXIS,
AND GRADUALLY TURNING SOUTHWARD WHILE SLOWING DOWN AS IT NEARS THE
WEAKEST STEERING GRADIENT AT THE RIDGE AXIS. THE SYSTEM IS FORECAST
TO CROSS THE RIDGE AXIS AND ACCELERATE SOUTHWARD AFTER TAU 12, THEN 
RECURVE SOUTHEASTWARD WHILE ACCELERATING THROUGH THE REMAINDER OF THE 
PERIOD AS IT INTERACTS WITH A TIGHTENING STEERING GRADIENT BETWEEN 
THE STR AND A DEEP MID-LATITUDE TROUGH. REGARDING INTENSITY, THE 
SYSTEM RAPIDLY INTENSIFIED OVER THE PAST 12 HOURS, INCREASING FROM 
65-90 KNOTS UNDER HIGHLY FAVORABLE ENVIRONMENTAL CONDITIONS, BUT TC 
27P HAS LIKELY REACHED ITS PEAK INTENSITY AT 0600Z. NORTHWESTERLY 
SHEAR IS STEADILY INCREASING, BRINGING DRY MID-LEVEL AIR IN WITH IT; 
HOWEVER, AS THE SYSTEM ACCELERATES AFTER TAU 12, VORTEX COHERENCE MAY 
BE SUSTAINED AS IT TEMPORARILY OUTPACES THE SHEAR. BY TAU 24, 
INCREASING SHEAR MAGNITUDE WILL MARK THE ONSET OF A RAPID CYCLOLYSIS 
PHASE. THE SYSTEM WILL BECOME SHEARED BY TAU 24, WITH DRY AIR 
ENTRAINMENT ENVELOPING THE REMNANT LOW-LEVEL VORTEX AS IT IS 
DISPLACED UNDER A STRONG JET STREAK. BY TAU 36, TC 29S WILL HAVE 
TRANSITIONED TO A WARM-CORE SECLUSION TYPE EXTRA-TROPICAL LOW. BY TAU 
36, TC 27P WILL HAVE TRANSITIONED TO A WARM-CORE SECLUSION TYPE 
EXTRA-TROPICAL LOW AS IT RACES POLEWARD. 

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, WHICH DEPICTS A FAR
TO WIDE OF A POLEWARD TURN, ALL OF THE AVAILABLE MODEL GUIDANCE IS
IN VERY STRONG AGREEMENT, WITH THE CONSENSUS MEMBERS CONFINED TO A
50NM WIDE CROSS-TRACK ENVELOPE AT TAU 36. THE JTWC FORECAST IS
CONSISTENT WITH THE MULTI-MODEL ENSEMBLE MEAN THROUGH THE FORECAST
PERIOD WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS A BIT MORE
MIXED, WITH THE HAFS-A DEPICTING A VERY SLOW AND GRADUAL WEAKENING
OF TC 27P, KEEPING IT ABOVE 50 KNOTS EVEN AS LATE AS 120 HOURS OUT.
THE COAMPS-TC AND HWRF ON THE OTHER HAND WEAKEN THE SYSTEM
EXTREMELY RAPIDLY, DOWN TO 40 KNOTS BY TAU 36. THE DECAY-SHIPS
TAKES A MORE REASONABLE MIDDLE GROUND, AND THE JTWC FORECAST IS
PLACED NEAR THE SHIPS AND THE CONSENSUS MEAN WITH HIGH CONFIDENCE. 

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