WDXS31 PGTW 260300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 033//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.9S 116.3E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 238 NM NORTH-NORTHEAST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LARGE
TROPICAL CYCLONE WITH DEEP CONVECTION WRAPPING AROUND THE RAGGED,
60 NM EYE. THE SYSTEM HAS MAINTAINED A SYMMETRIC CENTRAL DENSE
OVERCAST WITH MODERATE RADIAL OUTFLOW, THOUGH IT SEEMED TO HAVE
INGESTED SOME DRY AIR FROM ITS WEST. THIS LIKELY STALLED ITS RAPID
RATE OF INTENSIFICATION OVER THE PAST SIX HOURS. THE CLOUD TOPS HAVE 
COOLED SINCE THEN, WITH A RING OF WHITE AND COLD-MEDIUM-GRAY SHADES 
WRAPPING COMPLETELY AROUND THE EYE. RADAR RETURNS FROM THE KARRATHA 
RADAR NOW ENCIRCLE THE WELL-DEFINED INNER CORE. THIS SUGGESTS 
RESUMPTION OF INTENSIFICATION. A 252149Z RCM-1 SAR PASS DEPICTING A 
LARGE WIND FIELD WITH NEAR 100 KT WINDS IN THE SOUTHEAST QUADRANT AND 
THE T5.5 FROM PGTW WERE USED TO SET THE INITIAL INTENSITY OF 105 KTS 
WITH HIGH CONFIDENCE. THE INITIAL POSITION WAS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE CLEAR-CUT EYE FEATURE IN THE MSI IMAGERY.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE POSITIONED
OVER CENTRAL AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   APRF: T5.0 - 90 KTS
   CIMSS SATCON: 102 KTS AT 2520000Z
   CIMSS ADT: 122 KTS AT 260030Z
   CIMSS AIDT: 110 KTS AT 260030Z
   CIMSS D-PRINT: 100 KTS AT 260030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: DRY AIR TO THE SOUTHWEST

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 27P IS BEING STEERED TO THE SOUTHWEST BY A
LARGE ANTICYCLONE POSITIONED OVER CENTRAL AUSTRALIA AND IS
APPROACHING A WEAKNESS IN THE SUBTROPICAL RIDGE. THE TRAJECTORY OF
TC 27P WILL BECOME INCREASINGLY POLEWARD FROM TAU 12 TO TAU 24 AS
IT ACCELERATES DOWN THE WESTERN SIDE OF THE ANTICYCLONE. BY TAU 36,
IT WILL TURN SOUTH-SOUTHEASTWARD AS THE MID-LATITUDE WESTERLIES
BEGIN TO EXERT A STRONGER STEERING INFLUENCE. AS IT BECOMES
EMBEDDED IN THE MID-LATITUDINAL FLOW, IT WILL GAIN SUBTROPICAL
CHARACTERISTICS BY TAU 48 AND BECOME FULLY SUBTROPICAL BY TAU 72
WHEN IT EMERGES OVER THE GREAT AUSTRALIAN BIGHT. THE ENVIRONMENT
REMAINS HIGHLY CONDUCIVE FOR FURTHER INTENSIFICATION, CHARACTERIZED
BY VERY LOW VERTICAL WIND SHEAR AND VERY WARM SEA SURFACE
TEMPERATURES OF 30 DEGREES CELSIUS. THE SYSTEM HAS ABOUT 12 HOURS
TO INTENSIFY BEFORE IT ENCOUNTERS MORE HOSTILE CONDITIONS OF
INCREASING DEEP-LAYER SHEAR AND LAND INTERACTION. ALTHOUGH TC 27P
WILL PEAK CLOSE TO 261200Z AND WEAKEN PRIOR TO A LANDFALL ON
NORTHWESTERN AUSTRALIA, IT WILL MAKE A DEVASTATINGLY CLOSE APPROACH
TO LEARMONTH INSIDE 18 HOURS, WITH THE MOST POTENT QUADRANT TAKING
AIM AND INFLICTING POTENTIALLY HISTORIC IMPACTS ON THE EXMOUTH
PENINSULA. THE SYSTEM'S SHEER SIZE, DIRECTION OF TRAVEL, AND
LANDFALL POINT WILL EXACERBATE THE EFFECTS. AS IT ROUNDS THE RIDGE
AND TRAVELS TOWARDS GERALDTON, THESE CONDITIONS WILL LEAD TO RAPID
WEAKENING.

MODEL DISCUSSION: MODELS ARE IN TIGHT AGREEMENT ON BRINGING TC 27P
OVER THE EXMOUTH PENINSULA WITH A CROSS-TRACK SPREAD OF 30 NM.
AFTER TAU 36, THE AI MODELS REMAIN FIRM IN A MORE EASTWARD, INLAND
TRACK, WHILE THE GFS, ECMWF, AND THE MESOSCALE MODELS ARE FURTHER
TO THE WEST. THE FORECAST TRACK IS LAID WITH HIGH CONFIDENCE
THROUGH TAU 24 ON THE MULTI-MODEL CONSENSUS, THEN WITH LOWER 
CONFIDENCE FROM TAU 36 TO TAU 72. THE TRACK IS THEN HEDGED SLIGHTLY 
EAST OF THE CONSENSUS AND TOWARDS THE AI CLUSTER. THE INTENSITY 
GUIDANCE IS SPLIT AT TAU 12. HWRF PEAKS THE STORM AT 115 KTS, WHILE 
COAMPS-TC AND HAFS-A SUGGEST THAT STORM IS ALREADY PEAKING. THE 
FORECAST PEAK INTENSITY OF 120 KTS IS ABOVE MOST OF THE GUIDANCE AND 
CLOSEST TO THE RI AIDS AND HWRF. THE FORECAST RAPID WEAKENING PHASE 
AT TAU 36 IS CLOSER TO THE MULTI-MODEL CONSENSUS. THE INTENSITY 
FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE, GIVEN THE UNCERTAINTY 
ASSOCIATED WITH RATE OF DECAY OVER LAND.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM//

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