WDXS31 PGTW 221500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (CHARLOTTE) 
WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.5S 109.1E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 403 NM NORTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 36 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
MEDIUM-SIZED, ELONGATED SYSTEM WITH DEEP CENTRAL CONVECTION AND A
RAGGED EYE THAT HAS BECOME CLOUD-FILED. THE EIR LOOP ALSO INDICATES
SUBSIDENCE ALONG THE NORTHERN EDGES AND TRANSVERSE BANDING ALONG
THE SOUTHWESTERN PERIPHERIES, AN INDICATION OF INCREASING VERTICAL
WIND SHEAR. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON A MICROWAVE EYE IN THE 221112Z SSMIS PASS. THE INITIAL
INTENSITY OF 90KTS IS BASED ON THE PGTW 4.5-5.0 DVORAK ESTIMATE AND
REFLECTS A WEAKENING TREND.  ANALYSIS INDICATES A MARGINALLY
UNFAVORABLE ENVIRONMENT WITH THE STRONG POLEWARD OUTFLOW AND WARM
SST OFFSET BY MODERATE TO STRONG 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
UNFAVORABLE
   VWS: 20-25 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 24, 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 WITH AN EXPANDING WIND 
FIELD.  

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIRLY GOOD AGREEMENT UP
TO TAU 48; AFTERWARD, THEY DIVERGE SIGNIFICANTLY WITH SEVERAL
MODELS, INCLUDING AFUM, UKMET, EEMN 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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