WDXS31 PGTW 251500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 
031//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.9S 117.9E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 149 NM NORTH-NORTHWEST OF PORT HEDLAND,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 27P (NARELLE) AS IT PROPAGATES SOUTHWESTWARD UNDER THE
STEERING INFLUENCE OF A SUBTROPICAL RIDGE (STR) CENTERED OVER 
AUSTRALIA. THE SYSTEM HAS BEEN RAPIDLY INTENSIFYING AS WITNESSED BY
A 45 KTS MAXIMUM WIND SPEEDS OVER THE LAST 24 HOURS, WITH SIGNIFICANT 
IMPROVEMENT IN THE SIZE AND STRUCTURE OF THE CONVECTION, AS WELL AS 
DEVELOPMENT OF A BANDING EYE FEATURE. THE INITIAL POSITION AND 
INTENSITY ARE ASSESSED WITH HIGH CONFIDENCE BASED ON A 251039Z RCM-2 
SAR PASS SHOWING A 30-35 NM DIAMETER EYE, WITH PEAK INTENSITY OF 87-92 
KTS. A HIGHLY CONDUCIVE ENVIRONMENT IS FACILITATING THE TIGHT WRAPPING 
OF DEEP CONVECTIVE BANDS AROUND THE LOW-LEVEL CIRCULATION CENTER 
(LLCC). RAPID INTENSIFICATION (RI) IS SUPPORTED BY WARM (29-30 C) SEA 
SURFACE TEMPERATURES (SST), ROBUST RADIAL OUTFLOW, AND LOW (5-10 KTS) 
VERTICAL WIND SHEAR (VWS).

INITIAL WIND RADII BASIS: A 251039Z RCM-2 SAR PASS

CURRENT STEERING MECHANISM: DEEP LAYER SUBTROPICAL RIDGE (STR)
POSITIONED OVER CENTRAL AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   APRF: T4.0 - 65 KTS
   CIMSS ADT: 107 KTS AT 251140Z
   CIMSS AIDT: 100 KTS AT 251140Z
   CIMSS D-PRINT: 82 KTS AT 251300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

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 NARELLE IS FORECAST TO PROPAGATE
SOUTHWESTWARD TOWARDS THE NORTH WEST CAPE, WESTERN AUSTRALIA.
LANDFALL IN THE VICINITY OF THE PENINSULA IS ANTICIPATED AFTER TAU
24 AND JUST BEFORE TAU 36. FURTHER RAPID INTENSIFICATION IS
EXPECTED DUE TO A PERSISTENTLY CONDUCIVE ENVIRONMENT, AND THE
SYSTEM IS FORECAST TO REACH A PEAK INTENSITY OF 115-120 KTS BETWEEN
TAUS 24 AND 36. THE FORECAST TRACK IS POSITIONED SLIGHTLY WEST OF
THE TOWNS OF EXMOUTH AND LEARMONTH, WITH THE 64 KT WIND RADII STILL
FULLY ENCOMPASSING THE AREA. POST-LANDFALL, TC 27P WILL BEGIN TO
ROUND THE AXIS OF THE STEERING RIDGE AND TRACK SOUTHEASTWARD, OVER
LAND, THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD. A WEAKENING
TREND IS EXPECTED THROUGH TAU 96 DUE TO INCREASING VWS, DRY AIR
ENTRAINMENT AND TERRAIN-INDUCED FRICTION. BY TAU 96, TC 27P WILL
COMPLETE ITS EXTRATROPICAL TRANSITION (ETT), WHICH IS EXPECTED TO
COMMENCE AROUND TAU 72. THE SYSTEM IS FORECAST TO RE-EMERGE OVER
WATERS JUST SOUTH OF WESTERN AUSTRALIA WITH AN INTENSITY OF AROUND
45 KTS.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE HAS FURTHER
IMPROVED SINCE LAST WARNING AND IS NOW IN GOOD AGREEMENT THROUGHOUT
THE FORECAST PERIOD. THE CROSS-TRACK SPREAD AT LANDFALL IS
CURRENTLY AROUND 35 NM, EXPANDING TO 60 NM BY THE TIME TC 27P
REEMERGES OVER WATER SOUTH OF AUSTRALIA. MAJORITY OF THE GUIDANCE
ENSEMBLE MEMBERS INDICATE TRACK OVER WATER, CLOSELY ADJACENT TO THE
NORTH WEST CAPE, WITH MULTI-MODEL CONSENSUS AND AI CONSENSUS
TRACKERS PROJECTING LANDFALL SOUTHWEST OF LEARMONTH, AUSTRALIA.
JTWC OFFICIAL TRACK IS LAID VERY CLOSE TO THOSE TWO SOLUTIONS WITH
HIGH CONFIDENCE. REGARDING INTENSITY, THE OFFICIAL JTWC PREDICTION
IS ASSESSED WITH MEDIUM CONFIDENCE. ALL AVAILABLE MULTI-MODEL
CONSENSUS MEMBERS AGREE ON THE TIMELINE OF INTENSIFICATION AND
SUBSEQUENT DECAY; HOWEVER, WITH NUMEROUS RI-AIDS TRIGGERING AMIDST
MORE CONSERVATIVE DETERMINISTIC MODEL GUIDANCE, THE PEAK INTENSITY
SPREAD REMAINS WIDE, RANGING FROM 90 TO 130 KTS. THE JTWC FORECAST
IS LAID IN CLOSE PROXIMITY TO THE CONSENSUS THROUGHOUT THE FORECAST
PERIOD.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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