WDXS31 PGTW 102100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (IVONE) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.2S 81.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 929 NM SOUTH-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 31 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 24S WITH A COMPLETELY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) AS DEEP AND PERSISTENT CONVECTION HAS BECOME
INCREASINGLY DISLOCATED TO THE SOUTHEAST QUADRANT DUE TO THE
PRESENCE OF STRONG VERTICAL WIND SHEAR (VWS). WITH REGARD TO
UPPER-LEVEL SUPPORT, STRONG POLEWARD EXHAUST HAS CONTINUED, WITH
VISIBLE TRANSVERSE BANDING WRAPPING INTO A MID-LATITUDE JET FINGER
TO THE SOUTH AND RADIAL OUTFLOW STRIATIONS PULSING OUTWARD AND AWAY
FROM THE OFFSET CONVECTION. ALTHOUGH STRONG POLEWARD OUTFLOW HAS
HELPED MAINTAIN THE SYSTEMS INTENSITY, DRY-AIR ENTRAINMENT AND
HOSTILE VWS HAS CAPPED INTENSIFICATION TO 45 KTS. A RECENT 101647Z
ASCAT-C SCATTEROMETRY IMAGE HAS REVEALED AN ASYMMETRIC WIND FIELD,
RESTRICTING THE STRONGEST INTENSITIES TO THE SOUTHERN SEMICIRCLE.
THE INITIAL POSITION AND INTENSITY ARE ASSESSED WITH HIGH CONFIDENCE
BASED ON THE AFOREMENTIONED ASCAT-C IMAGE AND THE FULLY EXPOSED
LLCC ON ANIMATED EIR SATELLITE IMAGERY.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
POSITIONED TO THE EAST AND SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   DEMS: T2.5 - 35 KTS
   FMEE: T3.5 - 55 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS SATCON: 44 KTS AT 101600Z
   CIMSS ADT: 35 KTS AT 101830Z
   CIMSS AIDT: 37 KTS AT 101830Z
   CIMSS D-MINT: 40 KTS AT 101309Z
   CIMSS D-PRINT: 37 KTS AT 101830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT AROUND THE NORTHERN
SEMICIRCLE

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 24S IS FORECASTED TO CONTINUE ON A WESTWARD
TRACK ALONG THE NORTHERN PERIPHERY OF A BUILDING STR TO THE SOUTH
INTO TAU 36. AFTER TAU 36, THE SYSTEM WILL BEGIN ITS SOUTHWESTWARD
APPROACH TOWARD THE STR AXIS UNTIL TAU 72. AT THE SAME TIME, TC 24S
WILL BEGIN ITS INITIAL WEAKENING PHASE AS ENVIRONMENTAL CONDITIONS
BECOME LARGELY UNFAVORABLE FOR FURTHER INTENSIFICATION OR SUPPORT.
WHILE TC IVONE NEARS THE STR AXIS, THE UPPER-LEVEL OUTFLOW
MECHANISM WILL WEAKEN AS THE JET FINGER REPOSITIONS AND SHIFTS
SOUTHEASTWARD. WHILE THE CYCLONE ROUNDS THE STR AXIS AND BEGINS ITS
SOUTH-SOUTHEASTWARD TRACK AFTER TAU 72, SEA SURFACE TEMPERATURES
DECREASING TO BELOW 26 C, VERTICAL WIND SHEAR INCREASING TO
ABOVE 25 KTS, AND DRY AIR ENTRAINMENT WILL FURTHER WEAKEN THE
SYSTEM UNTIL TAU 96, RESULTING IN THE CYCLONES GRADUAL DISSIPATION.


MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE REMAINS IN TIGHT
AGREEMENT, WITH A 116 CROSS-TRACK SPREAD AS THE SYSTEM BEGINS ITS
SOUTHWEST APPROACH TOWARD THE STR AXIS AT TAU 72. AFTER TAU 72, THE
ALONG-TRACK INCREASES SUBSTANTIALLY BETWEEN JTWC CONSENSUS MEMBERS
AS THE SYSTEM STARTS TO BECOME COMPLETELY ENVELOPED INTO THE
MID-LATITUDE WESTERLIES. DUE TO THE UNCERTAINTY IN THE INTERACTION
BETWEEN TC 24S AND THE MID-LATITUDE WESTERLIES, THE JTWC TRACK
FORECAST IS ASSESSED WITH HIGH CONFIDENCE UNTIL TAU 72, AND
MODERATE CONFIDENCE THEREAFTER. WITH REGARD TO INTENSITY,
CONFIDENCE REMAINS HIGH THAT INTENSITIES WILL REMAIN NEAR 45 KTS 
UNTIL TAU 36. FOLLOWING TAU 36, NUMERICAL MODEL INTENSITY GUIDANCE
REMAINS IN GOOD AGREEMENT THROUGH THE REMAINDER OF THE FORECAST,
WITH AN EXPECTED AND STEADY WEAKENING PHASE AFTER TAU 36 AND UNTIL
COMPLETE DISSIPATION AT TAU 96.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: HIGH
   INTENSITY 72-120 HR: MEDIUM//
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