WDXS31 PGTW 210900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (CHARLOTTE) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.3S 111.1E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 453 NM NORTH-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS SPIRAL
BANDS OF DEEP CONVECTION WITH RADIAL OUTFLOW AND INCREASING
POLEWARD OUTFLOW. THE 210552Z AMSR2 89GHZ AND 36GHZ MICROWAVE IMAGES 
DEPICT A SLIGHTLY TILTED CORE STRUCTURE WITH A 7NM DIFFERENCE BETWEEN 
THE UPPER LEVEL CIRCULATION CENTER (ULCC) AND THE LOW LEVEL 
CIRCULATION CENTER (LLCC). A 210550Z AMSR2 WIND SPEED IMAGE DEPICTS 
THE BULK OF THE 55-61 KNOT WINDS ARE LOCATED IN THE SOUTHEASTERN 
SECTOR OF THE SYSTEM. THE INITIAL POSITION IS PLACED WITH HIGH 
CONFIDENCE BASED ON EIR AND MICROWAVE IMAGERY. THE INITIAL INTENSITY 
OF 60 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE AMSR2 WIND 
SPEED IMAGE. AGENCY DVORAK INTENSITY ESTIMATES REMAIN SLIGHTLY BELOW 
THE JTWC INITIAL INTENSITY POSSIBLY DUE TO THE AFOREMENTIONED TILT.

INITIAL WIND RADII BASIS: 210550Z AMSR2 WINDSPEED IMAGE

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   APRF: T3.5 - 55 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: INCREASING POLEWARD OUTFLOW INTO THE SUBTROPICAL
WESTERLIES 

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 21S (CHARLOTTE) IS FORECAST TO CONTINUE ITS
SOUTHWESTWARD TRACK UNDER THE STEERING INFLUENCE OF THE STR TO THE
SOUTHEAST. THERE IS STILL SOME POSSIBILITY OF RAPID INTENSIFICATION
THROUGH TAU 24 AS THE UPPER LEVEL OUTFLOW CONTINUES TO IMPROVE,
VERTICAL WIND SHEAR (VWS) REMAINS LOW AND SEA SURFACE TEMPERATURES
(SST) REMAIN WARM. AFTER REACHING ITS PEAK INTENSITY OF 85 KNOTS AT
TAU 24, THE STR TO THE SOUTHEAST BREAKS DOWN DUE TO AN APPROACHING
MID-LATITUDE TROUGH. AS THIS HAPPENS OUTFLOW WILL DETERIORATE AND
DRY AIR ENTRAINMENT WILL RESULT IN A SHARP WEAKENING TREND. NEAR TAU 
48, TC 21S WILL BEGIN TO INTERACT WITH THE MID-LATITUDE TROUGH, TURN 
SOUTH-SOUTHWESTWARD THROUGH TAU 72 AND INCREASE IN SPEED AND CONTINUE 
WEAKENING. BY TAU 96, THE SYSTEM WILL TRACK GENERALLY SOUTH-
SOUTHEASTWARD IN AN INCREASINGLY BAROCLINIC ENVIRONMENT WITH HIGH VWS 
(30-35 KTS) AND COOLER SST (26-27C), THEREFORE, TC 21S WILL CONTINUE 
TO WEAKEN THEN BECOME FULLY EMBEDDED IN THE MID-LATITUDE TROUGH AND 
COMPLETE SUBTROPICAL TRANSITION BY TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
SUPPORTING THE JTWC FORECAST TRACK WITH MEDIUM CONFIDENCE. THE JTWC
FORECAST TRACK IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS
(CONW). RELIABLE INTENSITY GUIDANCE IS IN FAIR AGREEMENT WITH THE
BULK OF THE MODELS SHOWING A SHARP INTENSIFICATION TREND THROUGH
TAU 12 TO TAU 24 THEN A RAPID WEAKENING TREND. THE JTWC INTENSITY 
FORECAST IS PLACED HIGHER THAN THE INTENSITY CONSENSUS (ICNW), WHICH 
IS SKEWED TOO LOW DUE TO COAMPS-TC (NAVGEM VERSION) AND AHNI. HWRF IS 
A NOTABLE OUTLIER, SHOWING A PEAK INTENSITY OF 98 KNOTS NEAR TAU 24. 

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