WDXS31 PGTW 122100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 29S (TWENTYNINE) 
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.0S 126.1E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 283 NM WEST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A NEARLY
FULLY EXPOSED, ELONGATED LOW-LEVEL CIRCULATION (LLCC) OF TC 29S.
THE ASSOCIATED DEEP CONVECTION IS DISPLACED TO THE SOUTH AND 
SOUTHWEST. THE SYSTEM APPEARS POORLY ORGANIZED, WITH DEVELOPMENT 
PRIMARILY HINDERED BY THE ELEVATED MID-LEVEL SHEAR. OTHER 
ENVIRONMENTAL PARAMETERS HOWEVER REMAIN MARGINALLY FAVORABLE, WITH 
WARM (29-30 C) SEA SURFACE TEMPERATURES (SST), DEEP AVAILABLE 
MOISTURE AND MODERATE POLEWARD OUTFLOW. THE INITIAL POSITION IS 
PLACED WITH MEDIUM CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC IN 
THE EIR IMAGERY LOOP, CONSISTENT WITH THE AREA OF CALM WINDS OBSERVED 
IN THE 121623Z GCOMW1 AMSR2 WIND SPEED PRODUCT. THE INITIAL INTENSITY 
OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY 
DVORAK FIXES AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
LOCATED OVER WESTERN AUSTRALIA, AS WELL AS ANOTHER STR TO THE
NORTHEAST OF THE SYSTEM

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   APRF: T2.0 - 30 KTS
   CIMSS SATCON: 37 KTS AT 121800Z
   CIMSS ADT: 35 KTS AT 121800Z
   CIMSS AIDT: 32 KTS AT 121800Z
   CIMSS D-MINT: 27 KTS AT 121654Z
   CIMSS D-PRINT: 29 KTS AT 121800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: 20-25 KTS MID-LEVEL SHEAR

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 29S IS FORECAST TO TRACK SOUTHWESTWARD OVER
THE NEXT 24 HOURS UNDER THE PRIMARY INFLUENCE OF THE STR TO THE
NORTHEAST. AFTER THAT, THE DEEP-LAYER STR TO THE SOUTH AND OVER
WESTERN AUSTRALIA WILL ASSUME STEERING AND NAVIGATE THE SYSTEM
WESTWARD. AROUND TAU 96 HOWEVER, A PASSING LONGWAVE TROUGH TO THE
SOUTH, WILL BREAK THE RIDGE AND PULL TC 29S SOUTHWARD, AND EVENTUALLY 
SOUTHEASTWARD, TOWARDS THE AUSTRALIA COASTLINE. IN TERMS OF INTENSITY, 
TC 29S IS FORECAST TO SLOWLY CONSOLIDATE, ORGANIZE AND INTENSIFY OVER 
THE NEXT 36 HOURS. AFTER THAT, THE MID-LEVEL SHEAR IS FORECAST TO 
WEAKEN, WITH ALL OTHER ENVIRONMENTAL CONDITIONS REMAINING FAVORABLE 
FOR FURTHER INTENSIFICATION, WHICH WILL RAPIDLY ACCELERATE, LEADING 
TO A FORECAST PEAK WIND SPEEDS OF 105 KTS. AFTER TAU 96, WHILE THE 
SYSTEM TURNS POLEWARD, CONDITIONS WILL DETERIORATE, WITH INCREASING 
WESTERLY WIND SHEAR AND THE INTRODUCTION OF DRY AIR INTO THE CORE OF 
THE VORTEX.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN FAIR AGREEMENT 
THROUGH THE INITIAL 72 HOURS. ALL MODELS AGREE ON A GENERAL 
SOUTHWESTWARD TRACK, FOLLOWED BY A WESTWARD TRACK. JTWC SHORT-TERM 
TRACK FORECAST IS LAID CLOSE TO THE MULTI-MODEL CONSENSUS WITH MEDIUM 
CONFIDENCE, DUE TO THE CROSS-TRACK SPREAD OF 90 NM AND ALONG-TRACK 
SPREAD OF 110 NM AT TAU 72. EXTENDED TRACK FORECAST IS ASSESSED WITH 
LOW CONFIDENCE DUE TO DRASTICALLY INCREASING GUIDANCE SPREAD. WHILE 
THE GFS ENSEMBLE IS THE FASTEST AND TAKES THE SYSTEM FURTHER 
WESTWARD, ECMWF DETERMINISTIC GUIDANCE IS ON THE OTHER END OF THE 
SPECTRUM, PREDICTING A SLOWER MOVEMENT, RESULTING IS SOUTHEASTWARD 
TURN MUCH CLOSER TO THE NORTHERN PORTION OF THE GREAT SANDY DESERT. 
SIMILARLY TO THE TRACK FORECAST, INTENSITY IS ALSO ASSESSED WITH 
MEDIUM CONFIDENCE IN THE SHORT-TERM, AND LOW CONFIDENCE THROUGHOUT 
TAUS 72 AND 120. ALL CONSENSUS MEMBERS INDICATE A SLOW, BUT STEADY 
INTENSIFICATION OVER THE NEXT 36-48 HOURS. AFTERWARDS HOWEVER, THE 
INTENSITY GUIDANCE SPREAD INCREASES TO 95 KTS, WITH HAFS BEING THE 
MOST AGGRESSIVE, PREDICTING PEAK OF 150 KTS, AND STATISTICAL-
DYNAMICAL MODELS ON THE LOWER END OF THE SPECTRUM, WITH ESTIMATES 
AROUND 55-60 KTS. JTWC FORECAST IS PLACED ON THE HIGHER END OF THE 
CONSENSUS, LEANING CLOSER TO THE GUIDANCE OF THE GFS, HWRF AND HAFS.

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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