WDPS31 PGTW 211500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.1S 136.8E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 347 NM EAST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 27P (NARELLE) WITH A FILLED EYE AND VIGOROUS BURSTS OF DEEP
CONVECTION NEAR THE CENTER. THE SYSTEM APPEARS TO HAVE MADE
LANDFALL ABOUT 50 NM SOUTH OF GOVE AIRPORT, NEAR CAPE SHIELD, AT
AROUND 211400Z. A TIMELY 211131Z METOP-B ASCAT PASS REVEALED THAT
THE STRONGEST WINDS REMAIN CONFINED TO THE EASTERN SEMICIRCLE OF
THE SYSTEM. THE INITIAL POSITION AND WIND RADII ARE BOTH PLACED
WITH HIGH CONFIDENCE BASED ON THE ASCAT DATA. THE INITIAL INTENSITY
OF 80 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY
DVORAK FIXES AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.
ENVIRONMENTAL ANALYSIS INDICATES THAT TC 27P IS NOW IN A MARGINAL
ENVIRONMENT CHARACTERIZED BY STRONG EQUATORWARD OUTFLOW ALOFT AND
WARM (29-30 C) SEA SURFACE TEMPERATURES GREATLY OFFSET BY TERRAIN
INTERACTION AND MODERATE (15-20 KTS) EASTERLY VERTICAL WIND SHEAR.

INITIAL WIND RADII BASIS: 211131Z METOP-B ASCAT SCATTEROMETER DATA

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED OVER CENTRAL AUSTRALIA. 


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   ABRF: T4.0 - 65 KTS
   CIMSS ADT: 79 KTS AT 211230Z
   CIMSS AIDT: 78 KTS AT 211230Z
   CIMSS D-PRINT: 80 KTS AT 211230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: TERRAIN INTERACTION

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC NARELLE IS FORECAST TO TRACK
WEST-SOUTHWESTWARD, ALONG THE NORTHERN PERIPHERY OF A STR TO THE
SOUTH THROUGH TAU 96. THE SYSTEM WILL TRACK ACROSS THE TOP END
THROUGH TAU 36, WHERE IT WILL EMERGE BACK OVER WATER WITHIN THE
SOUTHERN BONAPARTE GULF. A SECOND LANDFALL IS FORECAST TO OCCUR
NORTH OF WYNDHAM AROUND TAU 42. TC NARELLE IS ONCE AGAIN EXPECTED
TO EMERGE BACK OVER WATER, EAST OF ADELE ISLAND, NEAR TAU 60. THE
SYSTEM WILL THEN CONTINUE ON A WEST-SOUTHWESTWARD TRAJECTORY
THROUGH TAU 96 AS IT NEARS THE NORTHWESTERN EXTENT OF THE STR.
AFTER TAU 96, TC NARELLE WILL TURN MORE SOUTHWESTWARD AS IT
INITIATES A POLEWARD TRACK AROUND THE RIDGE AXIS. REGARDING
INTENSITY, NARELLE IS FORECAST TO RAPIDLY WEAKEN THROUGH TAU 24 AS
IT TRACK ACROSS THE TOP END. AN INTENSITY OF 35-40 KTS IS THEN
EXPECTED TO PERSIST THROUGH TAU 48 AS THE SYSTEM CONTINUES TO FEEL
THE EFFECTS OF TERRAIN INTERACTION AS IT TRACKS ALONG THE KIMBERLEY
COASTLINE. ONCE THE SYSTEM EMERGES BACK OVER WATER AROUND TAU 60,
THE ENVIRONMENT WILL QUICKLY IMPROVE. A COMBINATION OF WARM SEA
SURFACE TEMPERATURES, LOW SHEAR, AND STRONG OUTFLOW ALOFT, WILL
ALLOW FOR TC NARELLE TO REDEVELOP WITH A RAPID RATE OF
INTENSIFICATION AS IT APPROACHES THE EXMOUTH PENINSULA THROUGH TAU
120.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH TAU 72 WITH A CROSS-TRACK SPREAD OF 75 NM AND AN
ALONG-TRACK SPREAD OF 140 NM AT TAU 72. THE GFS ENSEMBLE MEAN
CONTINUES TO BE THE SLOWEST MODEL WHILE THE ECMWF DETERMINISTIC IS
THE FASTEST. AFTER TAU 72, MODELS BEGIN TO DIVERGE WITH TWO DISTINCT
GROUPINGS OF AI MODELS AND NON-AI MODELS. THE NON-AI MODELS TRACK
THE VORTEX FURTHER NORTH OF THE EXMOUTH PENINSULA BEFORE TURNING
POLEWARD. THIS SCENARIO APPEARS TO OCCUR DUE TO AN EXTENSION OF THE
STR OVER WESTERN AUSTRALIA EXTENDING WESTWARD, PREVENTING AN
EARLIER POLEWARD TURN. ON THE OTHER HAND, THE AI MODELS TRACK THE
VORTEX WITH A SHARPER TURN AROUND THE STR. THE EC-AIFS HAS THE
SHARPEST TURN AND DEPICTS THE SYSTEM MAKING LANDFALL WEST OF PORT
HEDLAND AROUND TAU 108. THE GOOGLE DEEPMIND ENSEMBLE MEAN IS
FURTHER WEST AND HAS THE SYSTEM ENTERING THE EXMOUTH GULF AT TAU
120. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL
CONSENSUS THROUGH TAU 72 AND THEN CLOSER TO THE GOOGLE DEEPMIND
ENSEMBLE MEAN THROUGH TAU 120 DUE TO ITS STRONG PERFORMANCE.
INTENSITY GUIDANCE GENERALLY AGREES ON RAPID WEAKENING THROUGH TAU
24, FOLLOWED BY A STEADY INTENSITY THROUGH TAU 48, AND QUICK
REDEVELOPMENT THROUGH TAU 120. INTENSITIES AT TAU 120 RANGE FROM 80
KTS (GFS) TO 115 KTS (HWRF). THE JTWC INTENSITY FORECAST IS PLACED
CLOSE TO THE CONSENSUS THROUGH TAU 72 AND THEN CLOSER TO HWRF AND
HAFS-A THROUGH TAU 120 DUE TO THE EXPECTED HIGHLY FAVORABLE
ENVIRONMENT AT THAT TIME.

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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