WDXS31 PGTW 261500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 035//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.4S 114.6E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 117 NM NORTH-NORTHEAST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 38 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A VERY
LARGE (40-45 NM) EYE FEATURE SURROUNDED BY NEARLY SYMMETRIC BANDS
OF DEEP CONVECTION. A 261021Z F17 SSMIS 91 GHZ MICROWAVE IMAGE
SHOWS THAT THE VORTEX HAS RETAINED ITS OVERALL STRUCTURE OVER THE
PAST 6 HOURS, WITH A LARGE AND SYMMETRIC MICROWAVE EYE FEATURE. THE
37 GHZ VERSION OF THE SAME MICROWAVE IMAGE REVEALED THAT THE
OUTER-EYEWALL THAT WAS PRESENT IN EARLIER MICROWAVE IMAGERY HAS
BECOME THE PRIMARY STRUCTURE, SUGGESTING THAT THE EYEWALL
REPLACEMENT CYCLE (ERC) HAS COMPLETED OR IS CLOSE TO COMPLETION. THE
ERC IS LIKELY THE REASON FOR THE CURRENT BROAD NATURE OF THE EYE.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
ANIMATED RADAR IMAGERY FROM LEARMONTH AND ANIMATED EIR IMAGERY
SHOWING THE CENTER POSITION OF THE BROAD EYE. THE INITIAL INTENSITY
OF 115 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY
DVORAK FIXES AND CIMSS OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.
THE CURRENT ENVIRONMENT IS CHARACTERIZED AS FAVORABLE DUE TO LOW
VERTICAL WIND SHEAR (VWS), WARM (28-29 C) SEA SURFACE TEMPERATURES,
AND STRONG POLEWARD OUTFLOW.

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

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE POSITIONED OVER WESTERN AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   APRF: T5.0 - 90 KTS
   CIMSS SATCON: 117 KTS AT 261021Z
   CIMSS ADT: 119 KTS AT 261200Z
   CIMSS AIDT: 113 KTS AT 261200Z
   CIMSS D-MINT: 114 KTS AT 261020Z
   CIMSS D-PRINT: 111 KTS AT 261200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   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 CONTINUED ON ITS
SOUTHWESTWARD TRAJECTORY OVER THE PAST 6 HOURS UNDER THE STEERING
INFLUENCE OF THE STR TO THE SOUTHEAST. LANDFALL ALONG THE EXMOUTH
PENINSULA IS EXPECTED JUST AFTER TAU 6, RESULTING IN A NEAR-DIRECT
HIT OF LEARMONTH BY THE MOST INTENSE LEFT-FRONT QUADRANT. THE
SYSTEM IS FORECAST TO ROUND THE STR AXIS AROUND TAU 12, THEN TURN
TO A SOUTHWARD TRACK THAT BECOMES SOUTH-SOUTHEASTWARD BY TAU 24.
AFTER TAU 24, TC NARELLE WILL ACCELERATE INLAND, EAST OF GERALDTON
AND PERTH, BEFORE EMERGING BACK OVER WATER SOUTH OF WESTERN
AUSTRALIA NEAR TAU 48. THE SYSTEM IS AT OR NEAR ITS PEAK INTENSITY,
WITH ONLY AROUND 6 HOURS UNTIL LAND INTERACTION AND COOLING SEA
SURFACE TEMPERATURES WILL INITIATE THE RAPID WEAKENING PHASE.
FURTHER WEAKENING WILL BE PROMOTED BY INCREASING WESTERLY VWS FROM
TAU 24 ONWARD. SUBTROPICAL TRANSITION IS FORECAST TO BEGIN AROUND
TAU 36 AND COMPLETE BY TAU 48 AS THE SYSTEM TRACKS SOUTHEAST OF
PERTH.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT
THROUGHOUT THE FORECAST PERIOD WITH A CROSS-TRACK SPREAD OF 40 NM
AT TAU 24 WHICH OPENS UP TO 120 NM AT TAU 48 AND ALONG-TRACK SPREAD
REMAINS MINIMAL. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE
TES1 MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE. MODEL INTENSITY
GUIDANCE AGREES ON WEAKENING THROUGH THE ENTIRE FORECAST PERIOD.
THE JTWC INTENSITY FORECAST IS PLACED NEAR THE CONSENSUS WITH
MEDIUM CONFIDENCE AS A RESULT OF INHERENT UNCERTAINTY IN THE RATE
OF DECAY OVER LAND.

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