WDXS31 PGTW 142100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (TWENTY) WARNING 
NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.7S 98.9E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 922 NM WEST-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS WELL
ORGANIZED CENTRAL DEEP CONVECTION WITH CURVED BANDING WRAPPING INTO
A DEFINED LOW LEVEL CIRCULATION CENTER (LLCC). THE EIR INDICATES
THAT TC 20S HAS BEEN ATTEMPTING TO ESTABLISH AN EYE OVER THE PAST
SIX HOURS. A SERIES OF RECENT MICROWAVE IMAGES, INCLUDING A 141814Z
AMSR 89 GHZ COLOR COMPOSITE PARTIAL PASS, REVEALS A WELL FORMED
MICROWAVE EYE PRESENT BELOW THE CLOUD COVER. THE AMSR WINDSPEED
PRODUCT HAS A BROAD SWATH OF 50 PLUS KNOT WINDS ALONG THE SOUTHEAST
QUADRANT, WITH A SMALL AREA OF 60 PLUS KNOT WINDS UNDER THE DEEPEST
CORE CONVECTION. UNFORTUNATELY THE PARTIAL COVERAGE DOES NOT ALLOW
FOR INTERROGATION IN THE WESTERN SIDE OF THE CONVECTION. THE
INITIAL POSITION WAS BASED ON THE PGTW EIR FIX AND SUPPORTED BY THE
MICROWAVE DATA WITH HIGH CONFIDENCE. THE INTENSITY IS ASSESSED AT
60 KNOTS BASED ON THE HIGH END OF THE PGTW DVORAK ESTIMATE OF T3.5
(55 KNOTS) GIVEN THE GOOD MICROWAVE STRUCTURE AND DEVELOPING EYE.
ADT IS TRENDING HIGHER, NOW AT 55 KNOTS, AND CIMSS SATCON IS 60
KNOTS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK. AMSR WINDSPEED
PRODUCT PROVIDES SUPPORTING DATA FOR WIND RADII IN SOUTHEAST
QUADRANT. NO RELIABLE SCATTEROMETRY DATA AVAILABLE AT THIS TIME.

CURRENT STEERING MECHANISM: ALONG AN EXTENSION OF A SUBTROPICAL
RIDGE CENTERED TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   APRF: T2.5 - 35 KTS
   CIMSS SATCON: 60 KTS AT 141537Z
   CIMSS ADT: 55 KTS AT 141740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 20S IS EXPECTED TO CONTINUE TRACKING ALONG
THE SUBTROPICAL RIDGE AXIS AND HAS A LIMITED WINDOW FOR FURTHER
DEVELOPMENT OVER THE NEXT 12-24 HOURS, AFTER WHICH AN APPROACHING
SHORT WAVE TROUGH IMPARTS INCREASING VERTICAL WIND SHEAR, IN
ADDITION TO A SIGNIFICANT DEGRADATION OF AVAILABLE MIDLEVEL 
MOISTURE. 
THE INTENSITY FORECAST IS INITIALLY HELD STEADY, ALTHOUGH IF A SOLID 
EYE DOES FORM THE PEAK INTENSITY WILL LIKELY BE REVISED HIGHER. 
BEYOND 
TAU 24, AS TC 20S WEAKENS, IT WILL CONTINUE THE SOUTHWESTERLY MOTION
UNDER A SHALLOWER MEAN FLOW REGIME, DESPITE A WEAKNESS IN THE RIDGE
THAT IS EXPECTED TO DEVELOP. GUIDANCE GENERALLY AGREES THAT TC 20S
WILL DISSIPATE OVER WATER BY TAU 72. 

MODEL DISCUSSION: NAVGEM AND AFUM ARE SOUTHERN OUTLIERS, TRACKING
TC 20S AROUND THE WEAKNESS IN THE SUBTROPICAL RIDGE. THE REST OF
THE GUIDANCE PACKAGE MAINTAINS SOUTHWESTERLY MOTION AND ARE IN GOOD
AGREEMENT ON THE DISSIPATION SCENARIO DESCRIBED. 

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