WDXS31 PGTW 252100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 032//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.3S 117.2E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 297 NM NORTHEAST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 36 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LARGE,
RAPIDLY CONSOLIDATING TROPICAL CYCLONE WITH DEEP CONVECTION
BUILDING AND WRAPPING AROUND A RAGGED 40 NM EYE. A TIMELY 251835Z GMI
PASS REVEALS A WELL-DEFINED INNER CORE WITH ROBUST CONVECTIVE BANDS
WRAPPING INTO THE CENTER, WITH A NOTEWORTHY POLEWARD SHIFT IN THE
TRACK. CONTINUED INTENSIFICATION IS EVIDENCED BY THE ENLARGING
CENTRAL DENSE OVERCAST, WARMING EYE, AND EXPANDING UPPER-LEVEL
OUTFLOW. HAVING INTENSIFIED 55 KTS IN THE LAST 24 HOURS, TC 27P
SHOWS NO INDICATION OF SLOWING DOWN WITHIN A HIGHLY FAVORABLE
ENVIRONMENT CHARACTERIZED BY VERY WARM SEA SURFACE TEMPERATURES OF
30 DEGREES CELSIUS AND VERY LOW VERTICAL WIND SHEAR OF 5 KTS. THE
INITIAL INTENSITY IS SET WITH MEDIUM CONFIDENCE SLIGHTLY HIGHER THAN 
THE DVORAK ESTIMATE OF T5.5 FROM PGTW, GIVEN THAT THE EYE TEMPERATURE 
HAS WARMED SINCE THE FIX. THE INITIAL POSITION IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE AFOREMENTIONED GMI PASS.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE POSITIONED
OVER CENTRAL AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   APRF: T5.0 - 90 KTS
   CIMSS SATCON: 105 KTS AT 251830Z
   CIMSS ADT: 122 KTS AT 251830Z
   CIMSS AIDT: 106 KTS AT 251830Z
   CIMSS D-MINT: 96 KTS AT 251726Z
   CIMSS D-PRINT: 97 KTS AT 251830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECASTED PEAK INTENSITY HAS BEEN 
INCREASED TO 125 KTS BASED ON THE HIGHER INITIAL INTENSITY.

FORECAST DISCUSSION: TC 27P IS NOW APPROACHING A WEAKNESS IN THE
SUBTROPICAL RIDGE AND BEGINNING TO ROUND THE NORTHWESTERN PERIPHERY
OF A STRONG ANTICYCLONE POSITIONED OVER CENTRAL AUSTRALIA. THE
FORECAST BRINGS THE SYSTEM TO A VERY CLOSE APPROACH TO THE EXMOUTH
PENINSULA, OVER WHICH THE MOST INTENSE SECTOR OF THE STORM WILL PASS. 
THE SYSTEM WILL CONTINUE TO TURN POLEWARD THROUGH TAU 36 AND THEN TURN
EASTWARD AS THE MID-LATITUDE WESTERLIES EXERT A STRONGER INFLUENCE.
TC WILL UNDERGO SUBTROPICAL TRANSITION AS IT PASSES EAST OF GERALDTON 
NEAR TAU 72 AND BECOME FULLY SUBTROPICAL BY TAU 96. THE IMMEDIATE 
CHALLENGE IS IN PREDICTING THE PEAK INTENSITY. WITH DEEP-LAYER SHEAR 
OF 5 KTS OR LESS, 30 DEGREE CELSIUS SEA SURFACE TEMPERATURES, AND 
SUFFICIENT MID-LEVEL MOISTURE, THE ENVIRONMENTAL CONDITIONS APPEAR TO 
BE HIGHLY CONDUCIVE FOR ADDITIONAL RAPID INTENSIFICATION (RI). GIVEN 
THAT TC 27P HAS HAD A HISTORY OF OVERPERFORMING EVEN THE HIGHEST 
ESTIMATES IN THE MODEL GUIDANCE, THE FORECAST CALLS FOR A PEAK OF 125 
KT BETWEEN 260600Z AND 261200Z. THE SYSTEM WILL INITIATE WEAKENING BY 
TAU 24 AS IT ENCOUNTERS DECREASING OCEAN HEAT CONTENT BUT WILL STILL 
BRING POTENTIALLY HISTORIC IMPACTS TO LEARMONTH. RAPID WEAKENING IS
PREDICTED AFTER TAU 24 DUE TO INCREASING VERTICAL WIND SHEAR AND
THE DRYING EFFECTS OF LAND. TOWARDS TAU 72, THE SYSTEM WILL BECOME
EMBEDDED WITHIN THE WESTERLIES AND GAIN SUBTROPICAL CHARACTERISTICS.

MODEL DISCUSSION: THE TRACK GUIDANCE IS IN TIGHT AGREEMENT THROUGH
TAU 24 WITH A 60 NM CROSS-TRACK SPREAD. THE AI MODELS FAVOR A
SHARPER TURN, WHILE THE PHYSICS-BASED MODELS ARE ON THE WESTERN
SIDE OF THE GUIDANCE ENVELOPE. NONETHELESS, ALL MODELS PREDICT AN
EXTREMELY CLOSE APPROACH TO OR A DIRECT LANDFALL ON LEARMONTH JUST
AFTER TAU 24. THE TRACK IS LAID WITH HIGH CONFIDENCE ON TOP OF THE
CONSENSUS (TES1) FOR THE FIRST 24 HOURS AND THEN HEDGED EAST OF THE
CONSENSUS AND CLOSER TO THE AI MODELS AFTER TAU 24. THE AVAILABLE 
GUIDANCE SHOWS CONTINUED INTENSIFICATION THROUGH TAU 24, AND SHIPS 
DEPICTS A NEARLY 60 PERCENT PROBABILITY OF A 20 KT INCREASE IN THE 
NEXT 12 HOURS. THE FORECAST PEAK IS SET ABOVE ALL OF THE MODEL 
GUIDANCE AND CLOSER TO THE RIDE RI MODEL. MODELS COMMENCE GRADUAL 
WEAKENING AT TAU 36, WITH MORE RAPID WEAKENING AS THE SYSTEM 
ACCELERATES POLEWARD OVER LAND. THE INTENSIFY FORECAST AFTER TAU 24 
IS CLOSE TO THE MULTI-MODEL CONSENSUS.

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