WDXS31 PGTW 260900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 034//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.6S 115.4E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 178 NM NORTH-NORTHEAST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LARGE 30
NM EYE WITH SYMMETRIC BANDS OF DEEP CONVECTION SURROUNDING THE
CENTER. A 260627Z AMSR2 89 GHZ MICROWAVE IMAGE REVEALS THAT THE
VORTEX HAS MAINTAINED ITS STRUCTURE, WITH A WELL-DEFINED INNER CORE
AND COLD CLOUD TOPS ENTIRELY SURROUNDING THE LOW-LEVEL CIRCULATION
CENTER (LLCC). THE 36 GHZ VERSION OF THE SAME MICROWAVE IMAGE
REVEALS THE SYSTEM IS UNDERGOING AN EYEWALL REPLACEMENT CYCLE, WITH
A DISTINCT MOAT FEATURE SEPARATING THE INNER AND OUTER EYEWALLS.
THE INITIAL INTENSITY OF 110 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
AND IS DERIVED FROM THE AGENCY DVORAK FIXES AND CIMSS OBJECTIVE
INTENSITY ESTIMATES LISTED BELOW. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON ANIMATED RADAR IMAGERY FROM KARRATHA,
THE AFOREMENTIONED AMSR2 IMAGE, AND ANIMATED MSI. THE CURRENT
ENVIRONMENT IS CHARACTERIZED AS FAVORABLE DUE TO LOW VERTICAL WIND
SHEAR (VWS), WARM (29-30 C) SEA SURFACE TEMPERATURES, AND RADIAL
OUTFLOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   APRF: T5.5 - 102 KTS
   CIMSS SATCON: 118 KTS AT 260600Z
   CIMSS ADT: 124 KTS AT 260600Z
   CIMSS AIDT: 113 KTS AT 260600Z
   CIMSS D-MINT: 116 KTS AT 260557Z
   CIMSS D-PRINT: 114 KTS AT 260600Z

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 27P (NARELLE) HAS TRACKED SOUTHWESTWARD
OVER THE PAST 6 HOURS ALONG THE NORTHWESTERN PERIPHERY OF THE
DEEP-LAYER STR OVER WESTER AUSTRALIA.  IT IS FORECAST TO CONTINUE
ROUNDING THE RIDGE AXIS THROUGH TAU 24 ON AN INCREASINGLY SOUTHWARD
TRAJECTORY. A FINAL LANDFALL WILL OCCUR ALONG THE EXMOUTH PENINSULA
JUST AFTER TAU 12, WITH THE LEFT-FRONT QUADRANT BRINGING LIKELY
DEVASTATING IMPACTS TO LEARMONTH AND SURROUNDING AREAS.  AFTER TAU
24 TC NARELLE IS FORECAST TO ACCELERATE SOUTH-SOUTHEASTWARD AROUND
THE SOUTHWESTERN PERIPHERY OF THE STR THROUGH THE REMAINDER OF THE
FORECAST PERIOD. THE SYSTEM IS EXPECTED TO REMAIN INLAND, EAST OF
GERALDTON AND PERTH. THE CURRENT INTENSITY OF 110 KTS AND A
FAVORABLE ENVIRONMENT FOR FURTHER INTENSIFICATION WILL RESULT IN A
PEAK INTENSITY OF 115-120 KTS LIKELY OCCURRING AROUND 261200Z.
INCREASING LAND INTERACTION FROM TAU 12 ONWARD WILL CAUSE RAPID
WEAKENING AS TC NARELLE PUSHES INLAND OVER WESTERN AUSTRALIA.
ADDITIONALLY, WESTERLY VWS (35-40 KTS) WILL QUICKLY INCREASE NEAR
TAU 36 AS THE SYSTEM INTERACTS WITH MID-LATITUDE WESTERLIES.
SUBTROPICAL TRANSITION IS FORECAST TO BEGIN AT TAU 36 AND COMPLETE
NEAR TAU 48 AS THE SYSTEM TRACKS SOUTHEAST OF PERTH.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN VERY GOOD AGREEMENT AT
TAU 12 WITH A CROSS-TRACK SPREAD OF 15 NM AND 20 NM OF ALONG-TRACK
SPREAD JUST BEFORE THE EXPECTED LANDFALL. AFTER TAU 12 NAVGEM
BECOMES AN OUTLIER, TRACKING THE SYSTEM ALONG THE AUSTRALIAN COAST
RATHER THAN INLAND AS DEPICTED BY THE REMAINDER OF GUIDANCE.
DISCOUNTING NAVGEM, THE CROSS-TRACK SPREAD STEADILY INCREASES TO
AROUND 70 NM AT TAU 48, WITH AN ALONG-TRACK SPREAD OF 115 NM. THE
AI AND PHYSICS-BASED MODELS HAVE COME INTO CLOSER AGREEMENT ON THE
TRACK COMPARED TO THE PREVIOUS MODEL RUN, LENDING HIGH CONFIDENCE
TO THE JTWC TRACK FORECAST WHICH IS PLACED NEAR THE TES1
MULTI-MODEL CONSENSUS. IN TERMS OF INTENSITY, GUIDANCE SUGGESTS
WEAKENING THROUGH TAU 12, HOWEVER, CONDITIONS ARE EXPECTED TO ALLOW
FOR EITHER A STEADY INTENSITY OR A BRIEF CONTINUATION OF
INTENSIFICATION DURING THIS PERIOD. FOLLOWING LANDFALL JUST AFTER
TAU 12, MODELS ARE IN VERY GOOD AGREEMENT ON RAPID WEAKENING. THE
JTWC INTENSITY FORECAST IS PLACED SLIGHTLY HIGHER THAN THE
CONSENSUS THROUGH TAU 12, THEN FOLLOWS CLOSE TO THE CONSENSUS
THROUGH THE REMAINDER OF THE FORECAST PERIOD. 

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