WDXS31 PGTW 270900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 038//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.6S 113.7E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 81 NM SOUTH-SOUTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: OVER LAND

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
CLOUD-FILLED EYE WITH DEEP CONVECTION SURROUNDING THE LOW-LEVEL
CIRCULATION CENTER (LLCC). THE FULL DIAMETER OF THE EYE MADE
LANDFALL SHORTLY BEFORE 270600Z IN THE VICINITY OF CORAL BAY. THE
ANIMATED MSI ALSO SHOWS STABLE STRATIFORM CLOUDS BEING ENTRAINED
FROM THE WEST INTO THE CORE OF THE VORTEX. THERE HAS BEEN A LACK OF
MICROWAVE IMAGERY AND WIND SPEED DATA FOLLOWING THE EARLIER 262200Z
SENTINEL-1A AND RCM-1 PASSES. HOWEVER, THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE ANIMATED MSI AND ANIMATED
RADAR IMAGERY FROM THE CARNARVON RADAR SITE. THE INITIAL INTENSITY
OF 85 KTS IS ASSESSED WITH LOW CONFIDENCE GIVEN THE LACK OF
SATELLITE DERIVED ESTIMATES OR NEARBY SURFACE OBSERVATIONS. THE
CURRENT ENVIRONMENT IS CHARACTERIZED AS HIGHLY UNFAVORABLE DUE TO
INCREASING (15-20 KTS) VERTICAL WIND SHEAR (VWS), DRY AIR
ENTRAINMENT FROM THE WEST, AND TERRAIN INTERACTION.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK AND NEARBY SURFACE
OBSERVATIONS

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   APRF: T5.0 - 90 KTS
   CIMSS D-PRINT: 80 KTS AT 270630Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 15-20 KTS
   SST: OVER LAND
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: TERRAIN INTERACTION AND DRY AIR ENTRAINMENT FROM
THE WEST

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 27P (NARELLE) HAS BEGUN ITS TURN TOWARD THE
SOUTH-SOUTHEAST AS IT TRANSITS OVER THE WESTERN COAST OF AUSTRALIA.
THE RATE OF ADVANCE IS FORECAST TO ACCELERATE AS THE SYSTEM MOVES
INLAND ALONG A SOUTH-SOUTHEASTWARD TRACK, EAST OF GERALDTON AND
PERTH, THROUGH TAU 24. NOW THAT LANDFALL HAS OCCURRED, LAND
INTERACTION, INCREASING WESTERLY VWS (UP TO 35-40 KTS), AND FURTHER
DRY AIR ENTRAINMENT FROM THE WEST WILL RESULT IN RAPID WEAKENING.
AN INTENSITY OF 45 KTS IS FORECAST AT TAU 24 AS THE SYSTEM PASSES
ABOUT 110 NM EAST OF PERTH WITH GALE-FORCE WINDS EXPECTED TO BE
CONFINED TO THE EASTERN SEMICIRCLE. A RAPID SUBTROPICAL TRANSITION
IS FORECAST TO BEGIN AROUND TAU 12 AND COMPLETE BY TAU 24 AS TC
NARELLE BECOMES A HYBRID WARM-CORE CYCLONE. 

MODEL DISCUSSION: THE TRACK GUIDANCE IS IN GOOD AGREEMENT ON A
SOUTH-SOUTHEASTWARD MOTION THROUGH THE ENTIRE FORECAST PERIOD WITH
A CROSS-TRACK SPREAD OF 50 NM AT TAU 24. THE MULTI-MODEL CONSENSUS
WAS USED TO SET THE JTWC FORECAST TRACK WITH HIGH CONFIDENCE. RAPID
WEAKENING IS INDICATED BY THE ENTIRE INTENSITY MODEL GUIDANCE
SUITE. THE JTWC INTENSITY FORECAST CLOSELY FOLLOWS THE MULTI-MODEL
CONSENSUS 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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