WDXS31 PGTW 241500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 
027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.4S 122.4E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 91 NM NORTH OF BROOME, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY REVEALS SPIRAL
BANDING OF DEEP CONVECTION UNDERGOING CONTINUOUS DEVELOPMENT AS THE
LOW-LEVEL CIRCULATION CENTER (LLCC) OF TROPICAL CYCLONE (TC) 27P
(NARELLE) IS TRANSITING OVER THE WARM (29-30 C) WATERS OF THE
INDIAN OCEAN, NORTHWEST OF THE DAMPIER PENINSULA, AUSTRALIA. CLOUD
TOPS HAVE BEEN COOLING, WHILE THE SIZE OF CONVECTIVE CANOPY IS
INCREASING AND FULLY OBSCURING THE LLCC. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED RADAR IMAGERY
FROM BROOME, AUSTRALIA AND EXTRAPOLATION FROM A 241123Z F16 SSMIS
37GHZ MICROWAVE PASS. THE INITIAL INTENSITY OF 45 KTS IS ALSO
ASSESSED WITH MEDIUM CONFIDENCE, BASED ON THE AVAILABLE OBJECTIVE
AND SUBJECTIVE INTENSITY ESTIMATES LISTED BELOW. ADDITIONAL 
ENVIRONMENTAL ANALYSIS REVEALS MODERATE, PRIMARILY WESTWARD AND 
POLEWARD OUTFLOW, LOW (10-15 KTS) VERTICAL WIND SHEAR (VWS) AND A DEEP 
MOISTURE LAYER PRESENT THROUGHOUT THE TROPOSPHERIC COLUMN.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   ADRM: T2.5 - 35 KTS
   CIMSS SATCON: 49 KTS AT 241124Z
   CIMSS ADT: 45 KTS AT 241130Z
   CIMSS AIDT: 39 KTS AT 241230Z
   CIMSS D-MINT: 49 KTS AT 241125Z
   CIMSS D-PRINT: 41 KTS AT 241230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE DUAL-CHANNEL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 IS FORECAST TO CONTINUE ITS TRAJECTORY
ALONG THE NORTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR)
CENTERED OVER AUSTRALIA, WHILE CONCURRENTLY UNDERGOING RAPID
INTENSIFICATION. A PEAK INTENSITY OF 100 KTS IS ANTICIPATED AROUND
TAU 48, JUST PRIOR TO THE SYSTEM ROUNDING THE RIDGE AXIS AND 
APPROACHING NORTH WEST CAPE, AUSTRALIA. A PERIOD OF RAPID 
INTENSIFICATION IS EXPECTED GIVEN THE HIGHLY CONDUCIVE ENVIRONMENTAL 
CONDITIONS FORECAST THROUGH TAU 48. MOST RECENT GUIDANCE VERY NARROWLY 
SHIFTS THE TRACK WESTWARD, WITH REMAINING POSSIBILITY FOR LANDFALL 
OVER WESTERN PORTION OF THE NORTH WEST CAPE, OR JUST TO THE SOUTH OF 
THE PENINSULA, CLOSER TO NINGALOO. AS THE SYSTEM ROUNDS THE RIDGE AXIS 
IT WILL BEGIN TRACKING SOUTHEASTWARD. SUBSEQUENTLY, THE SYSTEM IS 
EXPECTED TO WEAKEN DUE TO TERRAIN-INDUCED FRICTIONAL EFFECTS, 
INCREASING MID-LEVEL DRY AIR ENTRAINMENT, AND RAPIDLY INCREASING VWS 
ASSOCIATED WITH INTERACTION WITH THE SUBTROPICAL JET. AROUND TAU 96, 
SUBTROPICAL TRANSITION (STT) IS EXPECTED TO COMMENCE, WITH COMPLETION 
ANTICIPATED BY OR BEFORE TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN VERY GOOD
AGREEMENT FOR THE INITIAL 72 HOURS. THE CROSS-TRACK SPREAD AT TAU
72 IS 35 NM AND INCREASES TO 165 NM BY THE TIME TC NARELLE BEGINS ITS 
STT NEAR THE SOUTHWESTERN COAST OF AUSTRALIA. SIGNIFICANT IMPACTS TO
THE NORTH WEST CAPE REGION ARE STILL ANTICIPATED DESPITE THE SUBTLE
WESTWARD SHIFT IN THE TRACK FORECAST. REGARDING INTENSITY GUIDANCE, 
ALL MODELS REMAIN IN GOOD AGREEMENT ON THE TIMELINE FOR 
INTENSIFICATION, LANDFALL, AND SUBSEQUENT DECAY; HOWEVER, THE OFFICIAL 
JTWC INTENSITY FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE DUE TO A 35 
KT SPREAD IN PEAK INTENSITY GUIDANCE. THE MULTI-MODEL CONSENSUS 
INDICATES A PEAK INTENSITY OF 90 KTS. MULTIPLE RAPID INTENSIFICATION 
(RI) AIDS ARE TRIGGERED INDICATING HIGH CONFIDENCE IN RI POTENTIAL 
OVER THE NEXT 36 HOURS. NON-RI GUIDANCE (GFS, HAFS, COAMPS-TC AND 
STATISTICAL-DYNAMICAL MODELS) IS SLIGHTLY MORE CONSERVATIVE EXPECTING 
MAXIMUM WINDS NEAR 85-90 KTS. THE JTWC OFFICIAL FORECAST IS THEREFORE 
POSITIONED JUST ABOVE THE MULTI-MODEL CONSENSUS, ACCOUNTING FOR THE 
STRONG RI SIGNAL, WITH MEDIUM CONFIDENCE.

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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