WDXS31 PGTW 132100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (TWENTY) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.6S 103.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 807 NM NORTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CONSOLIDATING MEDIUM-SIZED SYSTEM WITH FORMATIVE BANDING WRAPPING 
TIGHTER INTO AN OBSCURED LOW LEVEL CIRCULATION (LLC) UNDER A 
DEEPENING CENTRAL CONVECTION. THE INITIAL POSITION AND INTENSITY ARE 
EXTRAPOLATED WITH HIGH CONFIDENCE FROM A 131429Z ASCAT BULLSEYE PASS 
THAT SHOWS A SYMMETRICAL LLC AND PATCHES OF 35-KT WIND BARBS ALONG 
THE SOUTHERN QUADRANTS. ANALYSIS INDICATES A FAVORABLE ENVIRONMENT 
WITH LOW VWS, WARM SST, AND MODERATE RADIAL OUTFLOW ALOFT. THE 
CYCLONE IS TRACKING ALONG THE NORTHWEST PERIPHERY OF THE STR TO THE
SOUTHEAST.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA.

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TC 20S WILL CONTINUE ON ITS CURRENT GENERALLY
WEST-SOUTHWESTWARD TRACK THROUGHOUT THE FORECAST. THE FAVORABLE
ENVIRONMENT WILL CARRY THROUGH TAU 36 AND FUEL A STEADY
INTENSIFICATION TO A PEAK OF 50KTS. AFTERWARD, INCREASING VWS WILL
OFFSET THE OTHER DYNAMICS AND ERODE THE SYSTEM DOWN TO 30KTS BY TAU
96.  

MODEL DISCUSSION: NUMERICAL MODELS ARE IN LOOSE AGREEMENT WITH
NAVGEM THE NOTABLE OUTLIER ON THE LEFT MARGIN OF THE MODEL ENVELOPE. 
AFUM AND UEMN INITIALLY START OUT WITH THE PACK UNTIL AFTER TAU 36 
WHERE THEY ABRUPTLY DIVERGE SOUTHWARD. THE MAJORITY OF THE MODEL 
MEMBERS ARE ON A WEST-SOUTHWESTWARD TRACK. IN VIEW OF THESE, THE 
JTWC TRACK FORECAST IS LAID WITH MEDIUM CONFIDENCE JUST NORTHWARD OF 
THE MODEL CONSENSUS AFTER TAU 36 TO OFFSET THE SOUTHWARD OUTLIERS. 
THERE IS LOW CONFIDENCE IN THE TRACK FORECAST BEYOND TAU 72 WHERE 
THE MODELS DIVERGE EVEN MORE.  

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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