WDXS31 PGTW 212100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (CHARLOTTE) 
WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.3S 109.8E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 435 NM NORTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
DEEP CONVECTION IN A CENTRAL DENSE OVERCAST WRAPPING AROUND A
LOW-LEVEL CIRCULATION CENTER (LLCC). TC 21S HAS RECENTLY DEVELOPED
A RAGGED EYE AS IT CONTINUES TO INTENSIFY. THE UPPER-LEVEL
STRUCTURE OF THE SYSTEM IS DEFINED BY GOOD RADIAL OUTFLOW WITH AND
ENHANCED POLEWARD OUTFLOW CHANNEL. THE INITIAL POSITION IS PLACED
WITH MODERATE CONFIDENCE GIVEN THE UNCERTAINTY ASSOCIATED WITH THE
CENTER OF THE DEVELOPING EYE. THE INITIAL INTENSITY OF 75 KNOTS IS
ASSESSED WITH HIGH CONFIDENCE GIVEN AGENCY DVORAK ESTIMATES OF T4.5
FROM PGTW AND APRF.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   APRF: T4.5 - 77 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   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 21S WILL CONTINUE TRACKING TOWARD THE
SOUTHWEST UNDER THE STEERING INFLUENCE OF THE STR TO THE SOUTHEAST
IN A MODERATELY FAVORABLE ENVIRONMENT. TC 21S HAS UNDERGONE A
SIGNIFICANT INTENSIFICATION PHASE, DEVELOPING A RAGGED EYE THAT HAS
WARMED OVER THE LAST COUPLE OF HOURS. GOOD RADIAL OUTFLOW WITH AN
ENHANCED POLEWARD OUTFLOW CHANNEL ALONG WITH WARM SEA SURFACE
TEMPERATURES AND LOW TO MODERATE VERTICAL WIND SHEAR SHOULD
CONTINUE TO SUPPORT INTENSIFICATION IN THE SHORT TERM WITH A
FORECAST PEAK INTENSITY OF 85 KNOTS BY TAU 12. HOWEVER, THE WINDOW
OF INTENSIFICATION WILL QUICKLY CLOSE BEYOND THAT TIME, WITH
INCREASED VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT INDUCED BY AN
APPROACHING MID-LATITUDE TROUGH. AROUND TAU 48, THE STR TO THE EAST
SHOULD WEAKEN AND TC 21S IS FORECAST TO TURN TOWARD THE SOUTH AND
EVENTUALLY TRACK TOWARD THE SOUTHEAST WITH AN INCREASE IN SPEED.
BEYOND TAU 72, THE INCREASINGLY BAROCLINIC ENVIRONMENT WILL INDUCE
SUBTROPICAL TRANSITION, AND TC 21S IS FORECAST TO COMPLETE
SUBTROPICAL TRANSITION BY TAU 96.

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, WHICH IS THE
WESTERN OUTLIER, NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT WITH
A 170NM SPREAD AT TAU 72, SUPPORTING THE JTWC FORECAST TRACK WITH 
MEDIUM CONFIDENCE. THE JTWC FORECAST TRACK IS POSITIONED CLOSE TO 
THE MULTI-MODEL CONSENSUS (CONW), BUT ACCOUNTING FOR THE NAVGEM 
OUTLIER. THE JTWC INTENSITY FORECAST IN THE NEAR TERM IS PLACED 
ABOVE THE BULK OF THE INTENSITY GUIDANCE, GIVEN THE CURRENT HEALTHY 
INNER CORE STRUCTURE OF THE SYSTEM AND THE LIKELIHOOD OF THE MODELS 
POSSIBLY OVERESTIMATING THE DEGREE OF DRY AIR ENTRAINMENT WITHIN THE 
NEXT 12 HOURS. BEYOND THE PEAK INTENSITY PERIOD, THE JTWC FORECAST 
TRACK REMAINS JUST ABOVE BUT FOLLOWS THE ENVELOPE OF THE INTENSITY 
CONSENSUS.

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