WDXS31 PGTW 242100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0S 121.5E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 67 NM NORTHWEST OF BROOME, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 27P (NARELLE) CONTINUES TO CONSOLIDATE OVER
WATER WEST OF THE DAMPIER PENINSULA AS DEPICTED BY ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY. DEEP CONVECTION PERSISTS
AND THE CIRCULATION HAS BEEN ABLE TO STRENGTHEN CONVECTIVE BANDING
SOUTH OF THE CENTER. OVER THE PAST SIX HOURS, CLOUD TOP
TEMPERATURES HAVE CONTINUED TO COOL AS 27P INTENSIFIES.
ENVIRONMENTAL CONDITIONS REMAIN HIGHLY FAVORABLE FOR CONTINUED
DEVELOPMENT WITH WARM SEA SURFACE TEMPERATURES BETWEEN 29 C AND 30
C, LOW VERTICAL WIND SHEAR (5-10 KTS), AND MODERATE RADIAL OUTFLOW.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON RADAR
DATA FROM BROOME, AUSTRALIA. THE INITIAL INTENSITY OF 50 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON A COMBINATION OF 241547Z
OSCAT SCATTEROMETER DATA, IMPROVED PRESENTATION NOTED VIA EIR
IMAGERY, AND AN UPTREND AMONGST SUBJECTIVE AND CIMSS OBJECTIVE
INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: 241547Z OSCAT SCATTEROMETER DATA

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 ADT: 59 KTS AT 241900Z
   CIMSS AIDT: 50 KTS AT 241730Z
   CIMSS D-MINT: 47 KTS AT 241409Z
   CIMSS D-PRINT: 41 KTS AT 241900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE 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: TROPICAL CYCLONE 27P WILL CONTINUE TO TRACK
SOUTHWESTWARD UNDER THE INFLUENCE OF THE SUBTROPICAL RIDGE (STR)
POSITIONED OVER CENTRAL AUSTRALIA UNTIL TAU 36. AFTERWARDS, THE
TRACK WILL TURN SOUTHWARD AS THE SYSTEM ROUNDS THE STR AXIS
CULMINATING IN THE FIFTH LANDFALL FOR THE SYSTEM OVER THE NORTH
WEST CAPE JUST AFTER TAU 48. AROUND TAU 72, CONTINUED DRY AIR
ENTRAINMENT ENHANCED BY INTERACTION WITH THE SUBTROPICAL JET WILL
INITIATE SUBTROPICAL TRANSITION OF THE SYSTEM. THE VORTEX MAY
RETAIN SOME TROPICAL CHARACTERISTICS UNTIL JUST AFTER TAU 72,
THOUGH THE TRANSITION IS FORECASTED TO BE COMPLETED BY TAU 96. TC
27P IS EXPECTED TO CONTINUE INTENSIFYING OVER THE NEXT 24 HOURS.
RAPID INTENSIFICATION REMAINS IN THE FORECAST, THOUGH THE EXPECTED
PERIOD FOR RAPID INTENSIFICATION HAS SHIFTED BACK TO BETWEEN TAU 24
AND TAU 36. THE PEAK INTENSITY IS FORECASTED TO BE 100 KTS AT TAU
36. AFTERWARDS, A STEADY INCREASE IN VERTICAL WIND SHEAR AND DRY
AIR ENTRAINMENT WILL START TO SLOWLY DECAY THE SYSTEM JUST BEFORE
LANDFALL. THE SYSTEM IS EXPECTED TO MAKE LANDFALL WITH AN INTENSITY
OF 95 KTS, THEN QUICKLY FALL TO 75 KTS AT AROUND TAU 72, AND
FINALLY COMPLETE SUBTROPICAL TRANSITION AROUND TAU 96 WITH 45 KTS
INTENSITIES. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE REMAINS IN GOOD
AGREEMENT WITH A CROSS-TRACK SPREAD UNDER 70 NM UNTIL TAU 72,
INCREASING TO 190 NM BY THE END OF THE FORECAST PERIOD. THE JTWC
FORECASTED TRACK IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH
HIGH CONFIDENCE UNTIL TAU 72 AND MEDIUM CONFIDENCE AFTERWARD DUE TO
UNCERTAINTIES REGARDING THE SHARPNESS OF THE SOUTHWARD TURN AROUND
THE STR AXIS AND THE EFFECTS OF SUBTROPICAL TRANSITION, ESPECIALLY
WITH THE INCREASED INFLUENCE FROM THE STJ NEAR TAU 72. INTENSITY
GUIDANCE IS ALSO IN GOOD AGREEMENT ON RAPID INTENSIFICATION BEFORE
TAU 36, THOUGH THERE IS A SPREAD BETWEEN 75 KTS AND 120 KTS ON PEAK
INTENSITIES. THE OFFICIAL JTWC INTENSITY FORECAST IS PLACED
SLIGHTLY ABOVE THE MULTI-MODEL CONSENSUS, BUT BELOW THE MORE
AGGRESSIVE RAPID INTENSIFICATION MODELS 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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