WDXS31 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 29S (TWENTYNINE) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.7S 126.4E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 445 NM NORTHEAST OF BROOME, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 29S WITH A RAGGED, PARTIALLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) THAT IS DISPLACED TO THE NORTH OF FLARING CONVECTION.
THE OVERALL STRUCTURE OF THE SYSTEM HAS CONTINUED TO FAIL TO
ORGANIZE OVER THE PAST 6 HOURS, LIKELY DUE TO THE PERSISTENT
MID-LEVEL SHEAR APPLYING PRESSURE ON THE VORTEX. ENVIRONMENTAL
ANALYSIS INDICATES THAT 29S IS IN A MARGINALLY FAVORABLE
ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD OUTFLOW ALOFT, THE
ELEVATED MID-LEVEL SHEAR, AND WARM (29-30 C) SEA SURFACE
TEMPERATURES. DETERMINISTIC MODEL AND CIMSS SHEAR ESTIMATES
CONTINUE TO SHOW LOW (5-10 KTS) DEEP-LAYER VERTICAL WIND SHEAR,
WHICH IS SOMEWHAT CONFLICTING WITH WHAT IS SEEN IN THE ANIMATED
SATELLITE IMAGERY. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC IN THE EIR IMAGERY.
THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH LOW CONFIDENCE
BASED ON THE DROPPING AGENCY DVORAK FIXES AND OBJECTIVE INTENSITY
ESTIMATES THAT ARE LISTED BELOW. BASED ON THE APPEARANCE OF THE
SYSTEM ALONE, IT COULD LIKELY BE BELOW TROPICAL STORM STRENGTH AT
THIS TIME.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: COMBINED INFLUENCE OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE NORTHEAST AND A STR POSITIONED TO THE
SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   APRF: T2.5 - 35 KTS
   CIMSS ADT: 47 KTS AT 121210Z
   CIMSS AIDT: 38 KTS AT 121210Z
   CIMSS DPRINT: 26 KTS AT 121210Z
   CIMSS DMINT: 26 KTS AT 121113Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: ELEVATED MID-LEVEL SHEAR

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: LOW
   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 CONTINUE ON A
WEST-SOUTHWESTWARD TRACK THROUGH TAU 24. TRACK SPEEDS ARE EXPECTED
TO INCREASE FOR TC 29S AS THE VORTEX REALIGNS. AN APPARENT JUMP IN THE 
TRACK COULD OCCUR IN RESPONSE TO THIS REALIGNMENT. AFTER TAU 24, THE
STEERING MECHANISM WILL SHIFT TO THE STR OVER WESTERN AUSTRALIA,
WHICH WILL DRIVE THE SYSTEM MORE WESTWARD THROUGH TAU 96. NEAR TAU
96, AN INCOMING LONG WAVE TROUGH IS EXPECTED TO BREAK DOWN THE
RIDGE AND CAUSE A SLOW POLEWARD TRACK MOTION THROUGH THE REMAINDER
OF THE FORECAST PERIOD. REGARDING INTENSITY, TC 29S IS FORECAST TO 
GRADUALLY INTENSIFY THROUGH TAU 48 TO AROUND 55 KTS CAPPED BY THE 
PRESENCE OF THE OF THE MID-LEVEL SHEAR. AFTER TAU 48, THE MID-LEVEL 
SHEAR IS EXPECTED TO LESSEN AND OUTFLOW IMPROVE, ALLOWING FOR FURTHER 
INTENSIFICATION, TO A PEAK OF AROUND 90 KTS AT TAU 84-96. NEAR TAU 84, 
WESTERLY SHEAR AND DRY AIR ENTRAINMENT ARE EXPECTED TO QUICKLY RISE IN 
RESPONSE TO THE INCOMING LONG WAVE TROUGH. THIS WILL CAUSE 29S TO 
RAPIDLY WEAKEN THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD AS THE 
SYSTEM BECOMES DECAPITATED AND SHEARED APART.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN MODERATE AGREEMENT
THROUGH TAU 72, WITH THE EXCEPTION OF NAVGEM, WHICH TRACKS THE
VORTEX MUCH FURTHER SOUTHWARD THAN THE REMAINDER OF GUIDANCE.
DISCOUNTING NAVGEM, THERE IS A 120 NM CROSS-TRACK SPREAD AT TAU 72.
AFTER TAU 72, MODELS BEGIN TO DIVERGE. GFS AND ITS ENSEMBLE MEAN
TRACK THE SYSTEM FURTHER WESTWARD WHILE ECMWF HAS THE VORTEX MAKING
A VERY SHARP POLEWARD TURN AT TAU 96. THE JTWC TRACK FORECAST IS
PLACED CLOSER TO THE ECMWF AND ITS ENSEMBLE MEAN TRACKERS NEAR THE
END OF THE FORECAST. THERE IS MEDIUM CONFIDENCE IN THE JTWC TRACK
THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER AS A RESULT. INTENSITY
GUIDANCE CONTINUES TO BE IN EXTREMELY POOR AGREEMENT. AT TAU 96
THERE IS A 105 KNOT SPREAD BETWEEN HAFS-A (155 KTS) AND HWRF (50
KTS). HAFS-A REMAINS THE PRIMARY OUTLIER THOUGH, WITH NO OTHER
MODEL SUGGESTING A RISE ABOVE 95 KTS. THE JTWC INTENSITY FORECAST
IS PLACED MORE IN LINE WITH THE GFS AND CLOSE TO THE MULTI-MODEL 
CONSENSUS WITH OVERALL LOW CONFIDENCE.

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