WDXS31 PGTW 170900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 29S (ERROL) WARNING NR 
023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.2S 119.4E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 228 NM NORTHWEST OF BROOME, AUSTRALIA
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 29S (ERROL) WITH A RAPIDLY DETERIORATING STRUCTURE AND A
FILLED EYE. CENTRAL CONVECTION REMAINS VIGOROUS BUT IS CERTAINLY
FEELING PRESSURE FROM THE NORTHWESTERLY VERTICAL WIND SHEAR. THE
170108Z METOP-C ASCAT IMAGE REVEALED THAT THE WIND FIELD IS
BECOMING INCREASINGLY ASYMMETRIC, ESPECIALLY WITH REGARDS TO THE
35-KNOT WIND RADII IN THE NORTHWESTERN QUADRANT. ENVIRONMENTAL
ANALYSIS INDICATES THAT 29S IS IN AN UNFAVORABLE ENVIRONMENT
CHARACTERIZED BY STRONG POLEWARD OUTFLOW AND WARM (29-30 C) SEA
SURFACE TEMPERATURES GREATLY OFFSET BY INCREASING VERTICAL WIND
SHEAR AND DRY AIR ENTRAINMENT. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON A 170533Z NOAA-21 ATMS MICROWAVE IMAGE
SHOWING THE DEFINED LOW-LEVEL STRUCTURE. THE INITIAL INTENSITY OF
105 KTS IS ASSESSED WITH LOW CONFIDENCE BASED ON THE RAPIDLY
WEAKENING APPEARANCE AND FALLING AGENCY DVORAK FIXES.

INITIAL WIND RADII BASIS: PERSISTENCE FROM THE 170108Z METOP-C
SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: EASTWARD STEERING PATTERN INFLUENCED BY
THE LONGWAVE TROUGH TO THE SOUTH OF THE SYSTEM.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   KNES: T6.0 - 115 KTS
   DEMS: T6.0 - 115 KTS
   APRF: T5.0 - 90 KTS
   CIMSS SATCON: 81 KTS AT 170535Z
   CIMSS ADT: 99 KTS AT 170600Z
   CIMSS AIDT: 92 KTS AT 170600Z
   CIMSS DPRINT: 100 KTS AT 170600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: BEGINNING OF DRY AIR ENTRAINMENT ALONG THE
WESTERN PERIPHERY OF THE SYSTEM

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: A QUICKER WEAKENING TREND THAN
PREVIOUSLY FORECASTED

FORECAST DISCUSSION: TC 29S IS FORECAST TO TRACK EAST-SOUTHEASTWARD
THROUGHOUT THE FORECAST PERIOD WITH INITIAL LANDFALL OCCURRING JUST
AFTER TAU 24 NEAR THE DAMPIER PENINSULA BEFORE AN ENTRANCE INTO THE
KING SOUND. REGARDING INTENSITY, TC 29S IS FORECAST TO RAPIDLY
WEAKEN OVER THE NEXT 24 HOURS TO AROUND 45 KTS DUE TO SHEAR
EXPECTED TO REACH VALUES UPWARDS OF 35-40 KTS AT TAU 24. DRY AIR
ENTRAINMENT FROM THE WEST IS ALSO EXPECTED TO QUICKLY INCREASE OVER
THE NEXT 24 HOURS, AIDING IN THE EROSION OF THE VORTEX. 29S IS THEN
FORECAST TO CONTINUE WEAKENING AS IT TRACKS INLAND WITH DISSIPATION
OCCURRING NO LATER THAN TAU 48 AS TERRAIN INTERACTION FURTHER
DIMINISHES THE SYSTEM.  

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH AN 80 NM CROSS-TRACK SPREAD AT TAU 24, NEAR THE TIME
OF LANDFALL. AFTER TAU 24, ALONG-TRACK SPREAD INCREASES SLIGHTLY,
BUT REMAINS IN OVERALL CONCURRENCE ON THE EAST-SOUTHEASTWARD TRACK.
AS A RESULT, THE JTWC TRACK FORECAST IS PLACED WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE AGREES ON A RAPID WEAKENING TREND,
THOUGH SOME MODELS (GFS AND COAMPS-TC) SUGGEST A DROP TO BELOW 35
KTS AS SOON AS TAU 30. THE JTWC INTENSITY FORECAST IS PLACED IN
LINE WITH MODEL CONSENSUS WITH MEDIUM CONFIDENCE DUE TO THE
POSSIBILITY FOR A QUICKER DISSIPATION TIMELINE.

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