WDXS31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 29S (INDUSA) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.6S 73.2E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 1019 NM EAST-NORTHEAST OF PORT LOUIS,
MAURITIUS
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SLOWLY
DEVELOPING TROPICAL CYCLONE (TC) 29S (INDUSA) PROPAGATING
SOUTHWESTWARD, STEERED BY A DEEP-LAYER SUBTROPICAL RIDGE (STR)
SITUATED TO THE SOUTHEAST. DESPITE AN OTHERWISE OVERWHELMINGLY
FAVORABLE ENVIRONMENT, DRY AIR ENTRAINMENT HAS SLOWED DOWN THE
EXPECTED INTENSIFICATION OVER THE LAST FEW HOURS. OCEANIC HEAT
CONTENT IS HIGH, WITH SEA SURFACE TEMPERATURES (SST) BETWEEN 29 C
AND 30 C, VERTICAL WIND SHEAR IS LOW AT 5-10 KTS, AND A ROBUST
UPPER-LEVEL POLEWARD OUTFLOW CHANNEL PERSISTS. OVER THE LAST COUPLE
HOURS STRONG CENTRAL CONVECTIVE BURST CAN BE SEEN INDICATING THE
SYSTEM POTENTIALLY TAPPING INTO ITS POTENTIAL AS THE ENVIRONMENTAL
CONDITIONS REMAIN HIGHLY CONDUCIVE FOR RAPID INTENSIFICATION. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE, INFERRED FROM
THE CURVATURE OF THE SPIRAL BANDING IN ANIMATED ENHANCED INFRARED
IMAGERY AND CORROBORATED BY EXTRAPOLATION FROM A 021114Z F18 SSMIS
37 GHZ MICROWAVE PASS. THE INITIAL INTENSITY OF 45 KTS IS ALSO
ASSESSED WITH MEDIUM CONFIDENCE, SUPPORTED BY THE DVORAK AGENCY
FIXES, OBJECTIVE ESTIMATES LISTED BELOW, AND SLIGHTLY IMPROVED
CONVECTIVE ACTIVITY.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: A DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   FMEE: T3.5 - 55 KTS
   CIMSS ADT: 53 KTS AT 021200Z
   CIMSS D-MINT: 41 KTS AT 021116Z
   CIMSS D-PRINT: 46 KTS AT 021200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG 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: TC 29S IS PROJECTED TO MAINTAIN ITS TRAJECTORY
ALONG THE NORTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE THROUGH
TAU 48. THE ENVIRONMENT IS FORECAST TO REMAIN EXCEPTIONALLY
FAVORABLE, SUPPORTING A PERIOD OF SUSTAINED, NEAR-RAPID
INTENSIFICATION, AS LONG AS THE SYSTEM MANAGES TO SHIELD ITS CORE
FROM ENTRAINING DRY AIR FROM THE WEST AND NORTH. PEAK INTENSITY IS
ASSESSED AT 85 KTS TO OCCUR AROUND TAU 48, JUST PRIOR TO A
SOUTH-SOUTHEASTWARD TRACK SHIFT AROUND THE AXIS OF THE RIDGE.
FOLLOWING THE TURN, TC INDUSA WILL BEGIN TO INTERACT WITH THE TAIL
END OF AN UPPER-LEVEL JET STREAM, INITIATING A WEAKENING TREND AND
THE ONSET OF EXTRATROPICAL TRANSITION (ETT). THE ATMOSPHERIC AND
OCEANIC ENVIRONMENT WILL BECOME INCREASINGLY HOSTILE, CHARACTERIZED
BY CONTINUOUS DRY AIR ENTRAINMENT FROM THE NORTH AND WEST, SHARPLY
INCREASING VERTICAL WIND SHEAR, AND A DECLINE IN SEA SURFACE
TEMPERATURES. PRIOR TO TAU 120, THE CIRCULATION FIELD IS EXPECTED
TO EXPAND AND BECOME ASYMMETRIC AS CORE WIND SPEEDS DIMINISH. TC
29S IS ANTICIPATED TO COMPLETE THE ETT SHORTLY BEFORE TAU 120, AS
IT BECOMES EMBEDDED WITHIN THE DEEP-LAYER WESTERLIES.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE DEMONSTRATES GOOD
AGREEMENT REGARDING THE FORECAST TRACK, EVIDENCED BY A TIGHT
INITIAL GUIDANCE ENVELOPE WITH A CROSS-TRACK SPREAD OF ONLY 50 NM
AT TAU 72, EXPANDING TO OVER 700 NM BY THE END OF THE FORECAST
PERIOD. THE LARGE ALONG-TRACK AND CROSS-TRACK SPREAD IS ATTRIBUTED
TO VARYING DEPICTION OF THE TIMELINE OF THE ETT BY THE AVAILABLE
GUIDANCE. WHILE THE INITIAL 72 HOURS FORECAST REMAINS REALLY GOOD,
THE LONG TERM TRACK OUTLIERS ARE UKMET DETERMINISTIC GUIDANCE
SHOWING A SLOWER, MORE SOUTHWARD TRACK, WHILE NAVGEM PROJECT A MUCH
FASTER AND EASTWARD PROPAGATION. OFFICIAL JTWC TRACK FORECAST IS
LAID CLOSE TO THE MULTI-MODEL CONSENSUS. AS FAR AS INTENSITY
FORECAST, IT IS SET WITH MEDIUM CONFIDENCE AND POSITIONED SLIGHTLY
ABOVE THE GUIDANCE MEAN, LEANING TOWARDS THE POSSIBILITY OF RAPID
INTENSIFICATION. WHILE ALL AVAILABLE MODELS CONCUR ON THE GENERAL
INTENSIFICATION AND DECAY TIMELINE, THE SPREAD IN PEAK INTENSITY IS
STILL SUBSTANTIAL, ESTIMATED AT 35 KTS. THE DETERMINISTIC GFS AND
STATISTICAL-DYNAMICAL MODELS FORECAST A PEAK OF ONLY 60-65 KTS, IN
STARK CONTRAST TO THE COAMPS-TC RI-AID, DTOP AND RIDE AIDS, WHICH
INDICATE A MAXIMUM INTENSITY OF 95-100 KTS. OFFICIAL JTWC INTENSITY
FORECASTS PEAK INTENSITY JUST 5-10 KTS LOWER THAN THE HAFS
PROJECTION, BUT SLIGHTLY HIGHER THAN THE OVERALL CONSENSUS MEAN.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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