WDXS31 PGTW 250900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 
030//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.8S 119.0E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 152 NM NORTH OF PORT HEDLAND, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY
INTENSIFYING TROPICAL CYCLONE (TC) 27P (NARELLE) AS IT TRANSITS
SOUTHWESTWARD UNDER THE INFLUENCE OF A STR CENTERED OVER AUSTRALIA.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A
WARMING, RUGGED EYE FEATURE DEVELOPING OVER THE LOW-LEVEL CIRCULATION 
CENTER (LLCC). HIGHLY FAVORABLE ENVIRONMENTAL CONDITIONS ARE ALLOWING 
THE SPIRAL BANDS OF DEEP CONVECTION TO TIGHTLY WRAP INTO THE LLCC. 
SUPPORTING THE RAPID INTENSIFICATION (RI) ARE WARM (29-30 C) SEA 
SURFACE TEMPERATURES (SST), STRONG RADIAL OUTFLOW AND LOW (5-10 KTS) 
VERTICAL WIND SHEAR (VWS). THE INITIAL INTENSITY OF 70 KTS IS ASSESSED 
WITH MEDIUM CONFIDENCE BASED ON THE COMBINATION OF AGENCY DVORAK AND 
OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: 250423Z OCEANSAT-3 OSCAT PASS

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   CIMSS SATCON: 78 KTS AT 250600Z
   CIMSS ADT: 99 KTS AT 250600Z
   CIMSS AIDT: 82 KTS AT 250600Z
   CIMSS D-MINT: 75 KTS AT 250600Z
   CIMSS D-PRINT: 71 KTS AT 250600Z

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: 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 IS FORECAST TO TRACK SOUTHWESTWARD AND
TOWARDS THE NORTH WEST CAPE, WESTERN AUSTRALIA. LANDFALL NEAR THE
PENINSULA IS EXPECTED SHORTLY AFTER TAU 36 AND THE TRACK OF THE
SYSTEM IS LAID SLIGHTLY TO THE WEST OF TOWNS OF EXMOUTH AND
LEARMONTH, WITH THE 64 KT WIND RADII LIKELY FULLY ENCOMPASSING THE
AREA. RAPID INTENSIFICATION IS EXPECTED TO CONTINUE DUE TO
CONTINUOUSLY FAVORABLE ENVIRONMENT AND THE SYSTEM IS EXPECTED TO
REACH PEAK INTENSITY OF 100-110 KTS BETWEEN TAUS 24 AND 36. AFTER
LANDFALL, TC NARELLE WILL BEGIN TO ROUND THE AXIS OF THE STEERING
RIDGE START TRACKING SOUTHEASTWARD THROUGHOUT THE REMAINDER OF THE
FORECAST. WEAKENING IS EXPECTED UNTIL TAU 96, DUE TO INCREASING
SHEAR, DRY AIR ENTRAINMENT, FRICTIONAL EFFECTS OF LAND INTERACTION
AND COOLER (26-27 C) SSTS TO THE SOUTH OF THE NORTH WEST CAPE
IMPACTING THE WESTERN PORTION OF THE CIRCULATION THAT REMAINS OVER
WATER. BY TAU 96 TC 27P WILL COMPLETE ITS EXTRATROPICAL TRANSITION
(ETT), WHICH IS EXPECTED TO BEGIN AROUND TAU 72. THE SYSTEM IS
EXPECTED TO REEMERGE OVER WATERS JUST SOUTH OF WESTERN AUSTRALIA,
WITH INTENSITY OF 35-40 KTS.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT IN THE SHORT TERM WITH JUST 40 NM CROSS-TRACK SPREAD AT
LANDFALL AND DETERMINISTIC ECMWF BEING THE MOST WESTERN OUTLIER,
KEEPING THE TRACK OFFSHORE UNTIL TAU 48. THE REMAINDER OF THE
GUIDANCE ENVELOPE, AS WELL AS THE AI MODELS INDICATE LANDFALL OVER
THE NORTH WEST CAPE, FOLLOWED BY A TURN INLAND. TRACK FORECAST
UNCERTAINTY INCREASES AROUND TAU 72, WITH THE GUIDANCE ENVELOPE
EXPANDING TO 180 NM. IN REGARD TO INTENSITY, OVERALL CONFIDENCE IN
THE OFFICIAL JTWC PREDICTION IS ASSESSED AS MEDIUM. ALL AVAILABLE
MULTI-MODEL CONSENSUS MEMBERS AGREE ON THE TIMELINE OF
INTENSIFICATION AND SUBSEQUENT WEAKENING, HOWEVER BETWEEN NUMEROUS
RI-AIDS TRIGGERING AND MORE CONSERVATIVE DETERMINISTIC MODEL
GUIDANCE, THE PEAK INTENSITY IS STILL SPREAD BETWEEN 90 AND 120
KTS. JTWC FORECAST IS LAID SLIGHTLY ABOVE, BUT CLOSE TO THE
MULTI-MODEL CONSENSUS THROUGHOUT THE FORECAST PERIOD.

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