WDXS31 PGTW 270300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 037//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.4S 113.6E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 28 NM WEST-SOUTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A NEARLY
CLOUD-FILLED, 30 NM EYE EMBEDDED WITHIN AN INCREASINGLY RAGGED,
ASYMMETRIC CENTRAL DENSE OVERCAST. COINCIDENT PASSES FROM
SENTINEL-1A AND RCM-1 AT 262200Z PROVIDED VALUABLE SAR DATA ON THE
EXTENT OF STORM- AND HURRICANE-FORCE WINDS. THE DOUBLE EYEWALL
FEATURE PREVIOUSLY OBSERVED IN SAR AND MICROWAVE PASSES ARE NO
LONGER APPARENT, SUGGESTING THAT THE DETERIORATION OF TC 27P HAS
DISRUPTED THE EYEWALL REPLACEMENT CYCLE. THE SAR DATA ALSO SUPPORTS
THE MSI IN DEPICTING THE EROSION OF THE INNER CORE AT THE NORTHWEST
QUADRANT. THE CENTER OF THE EYE IS MOVING SOUTHWARD AND SKIRTING
THE WESTERN COAST OF THE EXMOUTH PENINSULA, PASSING VERY NEAR POINT
CLOATES. THE SYSTEM REMAINS LARGE, AND IMPACTS EXTEND FAR AWAY FROM
THE CENTER. A MAXIMUM SUSTAINED WIND OF 80 KTS AND A GUST OF 104
KTS, WITH MINIMUM SEA LEVEL PRESSURE OF 965 MB, OCCURRED AT
LEARMONTH DURING THE CLOSEST POINT OF APPROACH BETWEEN 262200Z AND
262300Z. THE INITIAL POSITION WAS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE LARGE EYE OBSERVED IN THE MSI. THE INITIAL INTENSITY
IS SET AT 100 KTS WITH HIGH CONFIDENCE BASED ON THE WIND SPEED DATA
FROM THE DUAL SAR PASSES, SUPPORTED BY THE DROPPING FINAL T-NUMBERS
OF T5.0 FROM PGTW AND APRF.

INITIAL WIND RADII BASIS: SAR DATA AND SURFACE OBSERVATIONS

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
ANTICYCLONE OVER WEST-CENTRAL AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   APRF: T5.5 - 102 KTS
   CIMSS ADT: 112 KTS AT 262300Z
   CIMSS AIDT: 105 KTS AT 262300Z
   CIMSS D-MINT: 107 KTS AT 262136Z
   CIMSS D-PRINT: 96 KTS AT 270030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: INTERACTION WITH LAND

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: HAVING CROSSED THE SUBTROPICAL RIDGE AXIS, TC
27P WILL ACCELERATE TOWARDS THE SOUTH-SOUTHEAST ON THE WESTERN
PERIPHERY OF A LARGE ANTICYCLONE POSITIONED OVER CENTRAL AUSTRALIA,
PASSING INLAND OF SHARK BAY AT TAU 12. THE MID-LATITUDE WESTERLIES
WILL EXERT INCREASING INFLUENCE OVER THE STORM AND SHIFT ITS
DIRECTION OF MOTION MORE EAST OF SOUTH AT TAU 24 AND TAU 36. TC 27P
WILL COMMENCE RAPID SUBTROPICAL TRANSITION CLOSE TO TAU 24 AND
BECOME A HYBRID WARM-CORE SYSTEM BY TAU 36. RAPID WEAKENING IS
FORECAST AS THE SYSTEM INTERACTS WITH LAND AND WESTERLY VERTICAL
WIND SHEAR INCREASES CLOSE TO 40 KTS AFTER TAU 12. THESE FACTORS
AND A BOUNTIFUL AMOUNT OF DRY AIR WILL ERODE THE WESTERN HALF OF
THE INNER CORE BY TAU 24. THE SYSTEM SHOULD BROADEN OUT AND BECOME
FULLY SUBTROPICAL AT TAU 36.

MODEL DISCUSSION: THE TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH
THE FORECAST PERIOD, SHOWING A SOUTH-SOUTHEASTWARD MOTION FROM TAU
12 TO TAU 36 UNTIL THE SYSTEM REACHES THE GREAT AUSTRALIAN BIGHT.
THE MULTI-MODEL CONSENSUS WAS USED TO SET THE FORECAST TRACK WITH
HIGH CONFIDENCE. RAPID WEAKENING IS INDICATED BY THE ENTIRE MODEL
SUITE. THE INTENSITY FORECAST IS HEDGED TOWARDS THE HIGHER END OF
THE GUIDANCE, CLOSE TO HAFS-A, THROUGH TAU 24 AND IS THEN SET
CLOSER TO THE CONSENSUS AT TAU 36 WITH MEDIUM CONFIDENCE, GIVEN THE
UNCERTAINTY ASSOCIATED WITH RATE OF DECAY OVER LAND.

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

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