WDXS31 PGTW 250300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 029//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.4S 120.0E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 129 NM WEST-NORTHWEST OF BROOME, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 27P (NARELLE) HAS CONTINUED TO CONSOLIDATE
OVER THE PAST SIX HOURS WITH DEEP CONVECTIVE BANDING COMPLETELY
SURROUNDING THE CENTER AS DEPICTED ON ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI). CLOUD TOP TEMPERATURES CONTINUE TO COOL
AND THE ENVIRONMENT REMAINS HIGHLY FAVORABLE FOR CONTINUED
DEVELOPMENT WITH HIGH SEA SURFACE TEMPERATURES (29 C TO 30 C), LOW
VERTICAL WIND SHEAR (5-10 KTS), AND STRONG RADIAL OUTFLOW. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON ANIMATED
MSI OF THE LOW-LEVEL CIRCULATION CENTER (LLCC), CONSISTENT WITH
EARLIER 242236Z F16 SSMIS DATA AND SOUTHERLY WIND OBSERVATIONS FROM
ROWLEY SHOALS AT 240000Z. THE INITIAL INTENSITY OF 55 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON A PARTIAL 242140Z RCM-1
SAR PASS DEPICTING A MEAN VALUE OF 56 KTS.

INITIAL WIND RADII BASIS: 242140Z RCM-1 SAR DATA

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   CIMSS SATCON: 61 KTS AT 250100Z
   CIMSS ADT: 61 KTS AT 250100Z
   CIMSS AIDT: 54 KTS AT 250100Z
   CIMSS D-MINT: 55 KTS AT 242236Z
   CIMSS D-PRINT: 55 KTS AT 250100Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 WILL CONTINUE WEST-SOUTHWESTWARD UNDER
THE INFLUENCE OF THE DEEP LAYER SUBTROPICAL RIDGE (STR) POSITIONED
OVER CENTRAL AUSTRALIA UNTIL TAU 24. THE TRACK WILL THEN TURN
SOUTHWARD AS THE SYSTEM ROUNDS THE STR AXIS, RESULTING IN AN
EXPECTED LANDFALL FOR THE SYSTEM OVER NEAR EXMOUTH BETWEEN TAU 36
AND TAU 48. BETWEEN TAU 48 AND TAU 72, CONTINUED DRY AIR
ENTRAINMENT ENHANCED BY INTERACTION WITH THE SUBTROPICAL JET WILL
INITIATE EXTRATROPICAL TRANSITION OF THE SYSTEM, WITH THE
TRANSITION FORECASTED TO BE COMPLETE BY TAU 96. TC 27P IS EXPECTED
TO CONTINUE RAPIDLY INTENSIFYING OVER THE NEXT 36 HOURS. PEAK
INTENSITY IS FORECASTED TO BE 100 KTS AT TAU 36. AFTERWARDS, A
STEADY INCREASE IN VERTICAL WIND SHEAR, DRY AIR ENTRAINMENT, AND
COOLER SEA SURFACE TEMPERATURES (26 C TO 27 C) AROUND THE NORTH
WEST CAPE WILL START TO SLOWLY DECAY THE SYSTEM JUST BEFORE
LANDFALL. THE SYSTEM IS FORECAST TO MAKE LANDFALL WITH AN INTENSITY
OF 95 KTS, THEN QUICKLY DECAY FROM 85 KTS TO 50 KTS BETWEEN TAU 48
AND TAU 72 AS THE SYSTEM UNDERGOES ITS EXTRATROPICAL TRANSITION
WHILE TRANSITING THROUGH SOUTHWESTERN WESTERN AUSTRALIA. TC 27P IS
EXPECTED TO REEMERGE OFF THE SOUTHERN COAST OF WESTERN AUSTRALIA
INTO THE SOUTHERN OCEAN, AND WILL BE COMPLETELY EXTRATROPICAL BY
TAU 96 WITH 40 KTS INTENSITIES. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE AGREEMENT HAS
DEGRADED THIS RUN WITH CROSS-TRACK SPREAD INCREASING UP TO 100 NM
AROUND TAU 60 BEFORE DECREASING TO 50 NM AT TAU 72, SHOWING
INCREASING UNCERTAINTY REGARDING HOW FAR WESTWARD THE CENTER WILL
MOVE AROUND THE STR AXIS. AT THE END OF THE FORECAST PERIOD,
CROSS-TRACK SPREAD INCREASES TO 130 NM THROUGH EXTRATROPICAL
TRANSITION. THE JTWC FORECASTED TRACK IS PLACED CLOSE TO THE
MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE UNTIL TAU 72 AND LOW
CONFIDENCE AFTERWARD DUE TO UNCERTAINTIES REGARDING THE EFFECTS OF
EXTRATROPICAL TRANSITION, ESPECIALLY WITH THE INCREASED INFLUENCE
FROM THE STJ NEAR TAU 72. INTENSITY GUIDANCE IS IN GOOD AGREEMENT
ON RAPID INTENSIFICATION BEFORE TAU 24 WITH COAMPS-TC RAPID
INTENSITY PROBABILITIES SHOOTING UP TO 78 PERCENT IN THE LATEST
RUN. THERE IS A SPREAD BETWEEN 75 KTS AND 125 KTS ON PEAK
INTENSITIES. THE OFFICIAL JTWC INTENSITY FORECAST IS PLACED
SLIGHTLY ABOVE THE MULTI-MODEL CONSENSUS, BUT STILL BELOW THE MORE
AGGRESSIVE RAPID INTENSIFICATION MODELS WITH MEDIUM CONFIDENCE. 

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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