WDXS31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 29S (INDUSA) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.7S 70.3E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 755 NM EAST-SOUTHEAST OF PORT LOUIS,
MAURITIUS
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 20 KTS
   SIGNIFICANT WAVE HEIGHT: 29 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A HIGHLY
COMPACT VORTEX WITH AN IRREGULARLY SHAPED CENTRAL DENSE OVERCAST
(CDO). THE PINHOLE EYE THAT WAS PREVIOUSLY APPARENT HAS NOW BECOME
ENTIRELY CLOUD-FILLED. THE WESTERN HEMISPHERE OF THE SYSTEM
EXHIBITS A SHARP TRANSITION AT THE PERIPHERY OF THE CDO, INDICATIVE
OF THE HIGH VERTICAL WIND SHEAR (VWS) ENVIRONMENT. ANIMATED WATER
VAPOR IMAGERY CONTINUES TO DISPLAY ROBUST POLEWARD OUTFLOW. THE
INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC) IN ANIMATED EIR
IMAGERY. THE INITIAL INTENSITY OF 70 KTS IS ASSESSED WITH LOW
CONFIDENCE DUE TO THE COMPACT NATURE OF THE SYSTEM AND A LACK OF
WIND SPEED DATA. AGENCY DVORAK FIXES OF T4.0-4.5 SUPPORT THE
INITIAL INTENSITY ASSESSMENT. DESPITE THE EXCELLENT POLEWARD
OUTFLOW, THE CURRENT ENVIRONMENT IS ANALYZED AS UNFAVORABLE DUE TO
HIGH VWS, DRY AIR ENTRAINMENT, AND COOLING SEA SURFACE TEMPERATURES
(26-27 C).

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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: T4.0 - 65 KTS
   CIMSS ADT: 57 KTS AT 041800Z
   CIMSS AIDT: 65 KTS AT 041800Z
   CIMSS D-PRINT: 75 KTS AT 041800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE WEST

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 29S (INDUSA) HAS ROUNDED
THE RIDGE AXIS AND STARTED TRACKING SOUTH-SOUTHEASTWARD IN THE
PAST 6 HOURS UNDER THE STEERING INFLUENCE OF THE STR TO THE EAST.
IT IS FORECAST TO ACCELERATE ON A SOUTH-SOUTHEASTWARD TRACK THROUGH
TAU 12, THEN FURTHER ACCELERATE ON A MORE SOUTHEASTWARD TRACK
THROUGH TAU 24 AS IT INTERACTS WITH A DEEP MID-LATITUDE TROUGH
APPROACHING FROM THE WEST. THE STEADY WEAKENING TREND OF TC INDUSA
WILL CONTINUE THROUGH TAU 24 IN RESPONSE TO THE INCREASING VWS AND
DRY AIR ENTRAINMENT ASSOCIATED WITH THE MID-LATITUDE TROUGH. THE
SYSTEM IS FORECAST TO BEGIN EXTRATROPICAL TRANSITION NEAR TAU 12 AS
IT ENTERS COOLER (LESS THAN 26 C) SEA SURFACE TEMPERATURES AND
BECOMES ENGULFED BY DRY AIR. TRANSITION TO A WARM-CORE SECLUSION
TYPE EXTRATROPICAL LOW WILL BE COMPLETE AROUND TAU 24 AS SEA
SURFACE TEMPERATURES DROP BELOW 24 C.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT ON THE
GENTLY RECURVING TRACK TOWARD THE SOUTHEAST, WITH A CROSS-TRACK
SPREAD OF 70 NM AT TAU 24. THERE ARE NO SIGNIFICANT OUTLIERS AMONG
THE SUITE OF MODELS, LENDING HIGH CONFIDENCE TO THE JTWC TRACK
FORECAST, WHICH IS PLACED VERY CLOSE TO THE CONSENSUS MEAN. THE
MODEL INTENSITY GUIDANCE AGREES ON STEADY WEAKENING THROUGHOUT THE
FORECAST PERIOD. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE
MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE.

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