WDXS31 PGTW 250300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (TWENTYSEVEN) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.7S 110.0E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 408 NM NORTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS FRAGMENTED
SPIRAL CONVECTIVE BANDING WRAPPING INTO AN EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) OF TROPICAL CYCLONE (TC) 27S. THE
ASSOCIATED DEEP CONVECTION IS CONTAINED WITHIN THE WESTERN
SEMICIRCLE OF THE SYSTEM, DUE TO STRONG (20-25 KTS) AND PERSISTENT
NORTHEASTERLY VERTICAL WIND SHEAR (VWS). ENVIRONMENTAL CONDITIONS
REMAIN MARGINALLY FAVORABLE FOR TC INTENSIFICATION, WITH WARM
(29-30 C) SEA SURFACE TEMPERATURES (SST) AND STRONG POLEWARD
OUTFLOW CHANNEL, OFFSET ONLY BY THE AFOREMENTIONED VWS. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE ANIMATED HIGH
RESOLUTION VISIBLE IMAGERY. THE INITIAL INTENSITY OF 35 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND
OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) OVER
SOUTHWESTERN AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 38 KTS AT 242245Z
   CIMSS ADT: 35 KTS AT 242330Z
   CIMSS AIDT: 34 KTS AT 242330Z
   CIMSS D-MINT: 33 KTS AT 242243Z
   CIMSS D-PRINT: 33 KTS AT 250100Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 27S IS FORECAST TO REMAIN TRANSITING
WESTWARD ALONG THE NORTHWESTERN PERIPHERY OF THE STR CENTERED OVER
SOUTHWESTERN AUSTRALIA THROUGH TAU 36. AFTERWARDS, AN UPPER LEVEL
TROUGH PASSING TO THE SOUTH OF THE SYSTEM WILL BRIEFLY AND SLIGHTLY
WEAKEN THE STEERING. SHORTLY AFTER HOWEVER, ANOTHER UPPER-LEVEL
RIDGE WILL BUILD TO THE SOUTHWEST OF THE SYSTEM, PUSHING IT ON A WEST-
NORTHWESTWARD TRACK. AS TC 27S ROUNDS THE AXIS OF THE STR, IT WILL 
ONCE AGAIN TRACK WEST-SOUTHWESTWARD, THROUGHOUT THE REMAINDER OF THE 
FORECAST PERIOD. AS THE SYSTEM REMAINS IN RELATIVELY FAVORABLE 
ENVIRONMENT, IT IS FORECAST TO REACH 40 KTS WITHIN THE NEXT 12 HOURS 
AND MAINTAIN THIS INTENSITY THROUGH TAU 72, AS IT BALANCES BETWEEN 
WARM SST, GOOD OUTFLOW AND MODERATE TO STRONG VWS. WITHIN THE NEXT 24 
HOURS, TC 27S WILL BEGIN APPROACHING A REGION OF DRY AIR, WHICH WILL 
ALSO HINDER ANY SIGNIFICANT INTENSIFICATION. ADDITIONALLY, NEWEST 
TRACK GUIDANCE IS SLIGHTLY FURTHER NORTH THAN PREVIOUSLY FORECAST AND 
WITHIN A REGION OF MODERATE TO STRONG VWS. AS THE SYSTEM TURNS WEST-
SOUTHWESTWARD AROUND TAU 96, THE VWS WILL SUBSIDE, LEADING TO 
POTENTIAL FOR SLIGHT INTENSIFICATION. AT THE SAME TIME, THE IMPACTS OF 
DRY AIR ENTRAINMENT WILL BECOME MORE SIGNIFICANT, PUTTING A 50-55 KT 
CAP ON PEAK INTENSITY BETWEEN TAU 96 AND 120.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN FAIR
AGREEMENT IN REGARD TO THE TRACK, AS INDICATED BY A 100 NM
CROSS-TRACK SPREAD AT TAU 72, INCREASING TO 220 NM BY THE END OF
THE FORECAST PERIOD. JTWC TRACK FORECAST IS LAID WITH MEDIUM
CONFIDENCE, AND CLOSE TO THE MULTI-MODEL CONSENSUS, WHICH REFLECTS
THE PREVIOUSLY MENTIONED STEERING PATTERN INDICATED BY ALL OF THE 
CONSENSUS MEMBERS. IN REGARD TO INTENSITY, JTWC FORECAST IS ALSO 
ASSESSED WITH MEDIUM CONFIDENCE THROUGH TAU 120, AND CLOSE THE MULTI-
MODEL CONSENSUS, AS THE GUIDANCE FROM ALL MEMBERS HAS TIGHTENED. 
CURRENT INTENSITY SPREAD RANGES FROM 10 KTS AT TAU 24, TO 15 KTS AT 
TAU 120. GFS DETERMINISTIC GUIDANCE IS THE MOST CONSERVATIVE, WITH A 
PEAK INTENSITY OF 40 KTS REACHED AT TAU 108, WHILE HWRF IS THE MOST 
AGGRESSIVE, INDICATING HIGHEST WIND SPEEDS OF 55 KTS BETWEEN TAU 96 
AND 120.

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