WDXS31 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.1S 126.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 285 NM SOUTHWEST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: OVER LAND

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
CONVECTION CONFINED TO THE NORTHERN AND WESTERN PERIPHERIES ALONG
THE KIMBERLEY COASTLINE. THE LOW-LEVEL CIRCULATION CENTER IS
ANALYZED TO BE DISPLACED SLIGHTLY TO THE SOUTHEAST OF THE BULK OF
CONVECTION. A 231229Z METOP-B ASCAT PASS REVEALED 25-30 KT WINDS TO
THE NORTHWEST OF THE CENTER NEAR THE COAST. THE INITIAL POSITION IS
PLACED WITH LOW CONFIDENCE BASED ON THE ANIMATED EIR, DUE TO A LACK
OF MICROWAVE AND RADAR IMAGERY. THE INITIAL INTENSITY OF 35 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE OVERALL STRUCTURE AND
THE AFOREMENTIONED ASCAT PASS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   CIMSS D-PRINT: 43 KTS AT 231200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 10-15 KTS
   SST: OVER LAND
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: TERRAIN INTERACTION

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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 (NARELLE) CONTINUES ON A
WEST-SOUTHWESTWARD TRACK UNDER THE STEERING INFLUENCE OF THE STR TO
THE SOUTH. IT IS FORECAST TO CONTINUE WEST-SOUTHWESTWARD ALONG THE
KIMBERLEY COAST THROUGH TAU 12 WHERE IT WILL REEMERGE OVER THE
SOUTHERN INDIAN OCEAN, SOUTHEAST OF ADELE ISLAND. THE
WEST-SOUTHWESTWARD TRAJECTORY CONTINUES THROUGH TAU 72, THEN THE
SYSTEM BEGINS TO ROUND THE RIDGE AXIS INITIATING A POLEWARD TURN.
TC NARELLE IS FORECAST TO SKIRT THE WESTERN AUSTRALIA COASTLINE,
TRACKING JUST WEST OF THE EXMOUTH PENINSULA AND LEARMONTH AROUND
TAU 84. AFTER THE TAU 86 INFLECTION POINT THE SYSTEM WILL TRACK
SOUTHWARD AND ACCELERATE TOWARD GERALDTON ON A SOUTH-SOUTHEASTWARD
THROUGH TAU 120. A FINAL LANDFALL IS FORECAST TO OCCUR IN THE
VICINITY OF SHARK BAY AROUND TAU 96. IN TERMS OF INTENSITY, TC
NARELLE IS FORECAST TO MARGINALLY INTENSIFY OVER THE NEXT 24 HOURS
AS IT CONTINUES TO SKIRT THE COAST. ONCE THE SYSTEM HAS SUFFICIENT
DISTANCE FROM LAND, THE ENVIRONMENT WILL QUICKLY IMPROVE AND
SUPPORT REDEVELOPMENT. A STEADY RATE OF INTENSIFICATION WILL OCCUR
BETWEEN TAUS 24 AND 48, THEN A RAPID RATE OF INTENSIFICATION IS
FORECAST TO OCCUR THROUGH TAU 72 IN RESPONSE TO VERY LOW VERTICAL
WIND SHEAR (VWS) AND STRONG POLEWARD OUTFLOW. A PEAK INTENSITY OF
100-105 KTS IS LIKELY TO OCCUR SHORTLY AFTER TAU 72, WHICH IS NOT 
DIRECTLY CAPTURED BY THE CURRENT WARNING. AFTERWARD, COOLING SEA 
SURFACE TEMPERATURES, INCREASING WESTERLY VERTICAL WIND SHEAR, AND DRY 
AIR ENTRAINMENT, AND EVENTUAL LANDFALL WILL CAUSE THE SYSTEM TO WEAKEN 
THROUGH THE REMAINDER OF THE FORECAST PERIOD. TC NARELLE IS FORECAST 
TO BEGIN SUBTROPICAL TRANSITION AT TAU 96, WHERE IT BEGINS TO INTERACT 
WITH MIDLATITUDE WESTERLY WINDS AND CROSSES THE 26 C SST ISOTHERM. 
SUBTROPICAL TRANSITION IS FORECAST TO BE COMPLETE BY TAU 120 AS THE 
SYSTEM ACCELERATES SOUTHEASTWARD.

MODEL DISCUSSION: MODEL TRACK GUIDANCE REMAINS IN GOOD AGREEMENT
THROUGH TAU 48 WITH A CROSS-TRACK SPREAD OF 90 NM AND MINIMAL
ALONG-TRACK SPREAD. MODELS BEGIN TO DIVERGE AFTER TAU 48 WITH
CROSS-TRACK SPREAD INCREASING TO 190 NM AT TAU 72. THE CROSS-TRACK
SPREAD RAPIDLY WIDENS AFTER TAU 72 WITH AI MODELS MAINTAINING A
SHARPER TURN AROUND THE RIDGE AXIS WHILE THE PHYSICS-BASED MODELS
DEPICT A WIDER TURN. THE ECMWF DETERMINISTIC MODEL IS THE WESTERNMOST 
SOLUTION AND THE EC-AIFS COMPRISES THE EASTERNMOST. AFTER TAU 96 THE 
MODELS ARE IN VERY POOR AGREEMENT REGARDING TRACK SPEED, WITH THE EC-
AIFS AND GOOGLE DEEPMIND ENSEMBLE MEAN ACCELERATING THE VORTEX WELL TO 
THE SOUTHEAST OF PERTH AT TAU 120. ON THE OTHER HAND, THE GFS AND 
ECMWF ENSEMBLE MEANS ARE SOME 300 NM NORTH OF PERTH, CREATING AN 
ALONG-TRACK SPREAD OF 670 NM. THE JTWC TRACK FORECAST CLOSELY FOLLOWS 
THE TES1 CONSENSUS (WHICH ACCOUNTS FOR THE AI MODELS) THROUGH TAU 96. 
THE TAU 120 POSITION IS PLACED WITH EXTREMELY LOW CONFIDENCE - 
SLIGHTLY FASTER THAN THE GFS AND ECMWF ENSEMBLE MEANS. MODEL INTENSITY 
GUIDANCE CONTINUED TO IMPROVE IN AGREEMENT WITH THE LATEST RUN. THE 
MODELS AGREE ON GRADUAL INTENSIFICATION THROUGH TAU 24 FOLLOWED BY 
RAPID REDEVELOPMENT THROUGH TAU 72. PEAK INTENSITIES RANGE FROM 80-105 
KTS WITH COAMPS-TC (GFS BASED) BEING THE MOST AGGRESSIVE. MODELS ALSO 
AGREE ON STEADY WEAKENING AFTER TAU 72. THE JTWC INTENSITY FORECAST IS 
PLACED NEAR THE MULTI-MODEL CONSENSUS THROUGH TAU 48 THEN CLOSER TO 
THE COAMPS-TC SOLUTION THROUGH THE REMAINDER OF THE FORECAST PERIOD.

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