WDXS31 PGTW 262100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 036//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.1S 114.0E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 72 NM NORTH OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LARGE, 30
NM EYE EMBEDDED WITHIN A NEARLY SYMMETRIC CENTRAL DENSE OVERCAST
(CDO). WHILE THE EYE REMAINS WARM AND CIRCULAR, THE NORTHWEST
QUADRANT OF THE CDO IS ERODING, AND THE UPPER-LEVEL OUTFLOW IS
BECOMING INCREASINGLY RESTRICTED IN THE EASTERN SEMICIRCLE. THE
LEARMONTH AIRPORT RADAR REVEALS TWO CLOSED RAINBANDS SEPARATED BY A
MOAT, WITH NORTHERN SIDE OF THE PRIMARY EYEWALL OPENING UP. A
261722Z AMSR2 PASS ALSO SHOWS THESE FEATURES AND INDICATES AN ONGOING
EYEWALL REPLACEMENT CYCLE (ERC) THAT IS UNLIKELY TO COMPLETE BEFORE
THE SYSTEM MAKES LANDFALL. THE ERC LIKELY HALTED THE RAPID RATE OF
INTENSIFICATION OBSERVED UP UNTIL 260000Z, AFTER WHICH TIME THE TC 
PLATEAUED AT AROUND 110 KTS. THE SYSTEM IS MOVING INTO A MORE HOSTILE
ENVIRONMENT CHARACTERIZED BY INCREASING VERTICAL WIND SHEAR, COOLER
SEA SURFACE TEMPERATURES, AND LAND EFFECTS. UNFORTUNATELY, THESE
INITIAL SIGNS OF WEAKENING ARE COMING TOO LATE FOR LEARMONTH, WHERE 
DESTRUCTIVE SUSTAINED WINDS OF 75 KTS AND GUSTS OF 95-100 KTS ARE
ALREADY OCCURRING. THE RIGHT-FRONT QUADRANT IS ASSESSED TO BE OVER
THE EXMOUTH GULF, WHERE THE LARGE FETCH OF NORTHEASTERLY WINDS IS
PRODUCING HISTORIC COASTAL IMPACTS. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE LEARMONTH AIRPORT RADAR. THE
INITIAL INTENSITY IS SET AT 110 KTS WITH MEDIUM CONFIDENCE BASED ON
THE ONGOING ERC, THE T5.5 FROM APRF AND T6.0 FROM PGTW, AND THE
MAJORITY OF THE OBJECTIVE ESTIMATES FROM CIMSS RANGING FROM 107 KTS
TO 116 KTS.

INITIAL WIND RADII BASIS: PERSISTENCE AND SURFACE OBSERVATIONS

CURRENT STEERING MECHANISM: DEEP-LAYER ANTICYCLONE CENTERED OVER
WEST-CENTRAL AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   APRF: T5.5 - 102 KTS
   CIMSS SATCON: 116 KTS AT 261756Z
   CIMSS ADT: 112 KTS AT 261730Z
   CIMSS AIDT: 107 KTS AT 261730Z
   CIMSS D-MINT: 110 KTS AT 261757Z
   CIMSS D-PRINT: 107 KTS AT 261830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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: PUSHING INTO A WEAKNESS IN THE SUBTROPICAL
RIDGE, TC 27P IS ROUNDING THE NORTHWEST PERIPHERY OF A STRONG
ANTICYCLONE POSITIONED OVER WEST-CENTRAL AUSTRALIA. THE STORM
MOTION HAS SHIFTED SOUTH-SOUTHWEST, PRIMING TC 27P FOR AN IMMINENT
LANDFALL ON THE WESTERN COAST OF THE EXMOUTH PENINSULA. AFTER MAKING 
LANDFALL, THE SYSTEM WILL TURN TOWARDS THE SOUTH-SOUTHEAST AS IT 
INTERACTS WITH THE MID-LATITUDE WESTERLIES AND RAPIDLY UNDERGOES 
SUBTROPICALTRANSITION. IT WILL BECOME COMPLETELY SUBTROPICAL BY TAU 
48 OR EARLIER. THROUGH TAU 12, THE EFFECTS OF LAND INTERACTION AND
INCREASING VERTICAL WIND SHEAR WILL TAKE A TOLL ON THE INTENSITY OF
THE STORM. BY TAU 24, DEEP-LAYER, WESTERLY SHEAR SHOULD REACH 40
KTS. THE SYSTEM WILL BROADEN OUT AS IT TRACKS EAST OF PERTH AND
BAROCLINIC FORCING BECOMES A STRONGER DETERMINANT OF INTENSITY.

MODEL DISCUSSION: MODEL GUIDANCE IS IN TIGHT AGREEMENT THROUGH TAU
24. CROSS-TRACK SPREAD INCREASES TO 90 NM BY TAU 36, WITH THE ECMWF
AND EXPERIMENTAL AI MODELS ON THE EASTERN HALF OF THE SPREAD, AND
THE GFS AND MESOSCALE MODELS ON THE WESTERN HALF. THE FORECAST
TRACK IS LAID ON TOP OF THE CONSENSUS THROUGH TAU 48 WITH HIGH
CONFIDENCE. ALL MODELS DEPICT RAPID WEAKENING UNTIL THE SYSTEM
COMPLETES SUBTROPICAL TRANSITION. THE FORECAST INTENSITY IS SET
WITH MEDIUM CONFIDENCE ON THE HIGH END OF THE GUIDANCE SUITE
THROUGH TAU 12 AND HEDGED CLOSER TO THE CONSENSUS THEREAFTER.

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

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