WDXS31 PGTW 220900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (CHARLOTTE) 
WARNING NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.9S 108.9E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 437 NM NORTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 38 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN INTENSE,
MEDIUM-SIZED SYSTEM WITH DEEP CENTRAL CONVECTION AND A 15-NM RAGGED
EYE. THE OVERALL STRUCTURE IS ELONGATED SOUTHEASTWARD WITH STRONG
TRANSVERSE BANDING ALONG THE SOUTHWESTERN PERIPHERIES, AN
INDICATION OF STRONG VERTICAL WIND SHEAR DOWNSTREAM. THE INITIAL 
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON A MICROWAVE EYE 
IN THE 220551Z ATMS AND THE RAGGED EYE IN THE MSI LOOP, ADJUSTED FOR 
A
POLEWARD SLANT. THE INITIAL INTENSITY OF 90KTS IS BASED ON THE PGTW
DVORAK ESTIMATE AND REFLECTS THE OVERALL SUSTAINED CONVECTIVE
SIGNATURE. ANALYSIS INDICATES A MARGINALLY FAVORABLE ENVIRONMENT
WITH THE STRONG POLEWARD OUTFLOW AND WARM SST OFFSET BY MODERATE
VERTICAL WIND SHEAR. THE CYCLONE IS TRACKING ALONG THE NORTHWEST
PERIPHERY OF THE STR TO THE SOUTHEAST.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP LAYER SUBTROPICAL RIDGE (STR) TO
THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 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 CHARLOTTE WILL CONTINUE SOUTHWESTWARD UNDER
THE STEERING INFLUENCE OF THE STR. AFTER TAU 36, THE SYSTEM WILL
ROUND THE STR AXIS AND TRACK SOUTHWARD THEN SOUTHEASTWARD TOWARD
PERTH, AUSTRALIA. THE ENVIRONMENT WILL BECOME MORE UNFAVORABLE WITH
INCREASING VWS AND COOLING ALONG-TRACK SST, LEADING TO A GRADUAL
THEN RAPID WEAKENING. CONCURRENTLY, THE CYCLONE WILL BEGIN
SUBTROPICAL TRANSITIONS BY TAU 72, AND BY TAU 96, TC 21S WILL BE
REDUCED TO A 35-KNOT SUBTROPICAL SYSTEM.  

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIRLY GOOD AGREEMENT UP
TO TAU 48; AFTERWARD, THEY DIVERGE SIGNIFICANTLY WITH SEVERAL
MODELS, INCLUDING AFUM, UKMET, AND ECMF, DEPICTING ERRATIC
REVERSALS IN THE STORM MOTION. IN VIEW OF THIS, THERE IS MEDIUM
CONFIDENCE IN THE JTWC TRACK FORECAST UP TO TAU 72, THEN LOW
CONFIDENCE AFTERWARD. 

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