WDXS31 PGTW 120900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 29S (TWENTYNINE) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.5S 126.6E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 461 NM NORTHEAST OF BROOME, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 29S WITH A SLIGHTLY DEGRADED APPEARANCE COMPARED TO 6-12
HOURS AGO. THE NORTHERN PORTION OF THE CIRCULATION HAS BECOME
EXPOSED AND IS A BIT RAGGED, WITH THE LOW-LEVEL CLOUD LINES LOOSELY
WRAPPING INTO THE CENTER. THE CONVECTION IS NOW DISPLACED TO THE
SOUTHEAST OF THE LOW-LEVEL CIRCULATION CENTER (LLCC) BUT CONTINUES
TO BE VIGOROUS WITH VERY COLD CLOUD TOPS (NEAR -90 C).
ENVIRONMENTAL ANALYSIS INDICATES THAT 29S IS IN A MARGINALLY
FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD OUTFLOW
ALOFT, LOW (10-15 KTS) DEEP LAYER SHEAR, AND WARM (29-30 C) SEA
SURFACE TEMPERATURES. HOWEVER, MODELS ARE PICKING UP ON ELEVATED
(20-25 KTS) EASTERLY VERTICAL WIND SHEAR, WHICH IS APPARENT IN THE
ANIMATED MSI. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON THE SLIGHTLY RAGGED, PARTIALLY EXPOSED LLCC. THE INITIAL
INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
PERSISTENCE FROM EARLIER ASCAT IMAGERY AND THE DROPPING FINAL-T
ESTIMATES FROM ALL FIXING AGENCIES TO A T2.5 VALUE.

INITIAL WIND RADII BASIS: PERSISTENCE FROM 120017Z METOP-B ASCAT
IMAGERY.

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF SUBTROPICAL
RIDGE (STR) POSITIONED TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   APRF: T3.0 - 45 KTS
   CIMSS ADT: 51 KTS AT 120600Z
   CIMSS AIDT: 40 KTS AT 120600Z
   CIMSS DPRINT: 33 KTS AT 120640Z

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

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

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 TRACKING
WEST-SOUTHWESTWARD, ALONG THE SOUTHWESTERN PERIPHERY OF THE STR TO
THE SOUTHEAST THROUGH TAU 36. NEAR TAU 48, THE STEERING MECHANISM
SHIFTS TO AN EXTENSION OF A STR OFF TO THE WEST-SOUTHWEST. THIS
WILL CAUSE 29S TO TRACK 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. REGARDING INTENSITY, TC 29S IS
FORECAST TO GRADUALLY INTENSIFY THROUGH TAU 36 TO AROUND 50 KTS DUE
TO THE PRESENCE OF THE OF THE MID-LEVEL SHEAR. AFTER TAU 36, THE
MID-LEVEL SHEAR IS EXPECTED TO LESSEN, ALLOWING FOR FURTHER
INTENSIFICATION, TO A PEAK OF AROUND 90 KTS AT TAU 96. NEAR TAU 96,
WESTERLY SHEAR AND DRY AIR ENTRAINMENT ARE EXPECTED TO QUICKLY RISE
IN RESPONSE TO THE INCOMING LONG WAVE TROUGH. THIS WILL CAUSE 29S
TO 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
REGARDING THE TRACK OF 29S THROUGH TAU 72 WITH A CROSS-TRACK SPREAD
OF 200 NM. AFTER TAU 72, MODELS BEGIN TO DIVERGE, WITH SOME MODELS
PREDICTING A MUCH SHARPER POLEWARD TURN. THE ECMWF TURNS THE SYSTEM
SHARPLY POLEWARD WHILE GFS TAKES THE VORTEX FURTHER WESTWARD WITH A
SHALLOWER TURN. NAVGEM IS AN OUTLIER AT THIS POINT, KEEPING THE
VORTEX MUCH CLOSER TO THE COAST THAN THE REMAINDER OF GUIDANCE. THE
JTWC TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE THROUGH TAU 72
AND LOW CONFIDENCE THEREAFTER. INTENSITY GUIDANCE IS IN POOR
AGREEMENT. PARTICULARLY AFTER TAU 60. HAFS-A SUGGESTS A PEAK
INTENSITY OF NEAR 150 KTS AT TAU 96 WHILE GFS SUGGESTS A PEAK OF 95
KTS. COAMPS-TC IS ERRONEOUSLY LOW, SUGGESTING A PEAK OF AROUND 45
KTS AT TAU 36 AND WEAKENING AFTERWARDS. THE JTWC INTENSITY FORECAST
IS MORE IN LINE WITH THE GFS 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//
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