WDPS31 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.4S 155.3E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 614 NM EAST-NORTHEAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A LARGE
CENTRAL DENSE OVERCAST (CDO) FEATURE DEVELOPING OVER THE LOW-LEVEL
CIRCULATION CENTER (LLCC). CLOUD TOP TEMPERATURES ARE MEASURING
COLDER THAN -90 C IN MULTIPLE AREAS IN CLOSE PROXIMITY TO THE
ASSESSED CENTER. TC NARELLE HAS BECOME MORE VERTICALLY ALIGNED WITH
A MUCH MORE SYMMETRIC APPEARANCE OVER THE PAST 12 HOURS.  A 171113Z
METOP-B ASCAT IMAGE REVEALED A COMPACT INNER CORE WITH 50 KTS WIND
VECTORS TO THE SOUTH OF THE LLCC. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE TIMELY ASCAT PASS. THE INITIAL
INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AFOREMENTIONED ASCAT PASS ALONG WITH THE AGENCY DVORAK FIXES AND
CIMSS INTENSITY ESTIMATES LISTED BELOW. CURRENT ENVIRONMENTAL
CONDITIONS ARE ANALYZED TO BE FAVORABLE, CHARACTERIZED BY LOW (5-10
KTS) DEEP-LAYER VERTICAL WIND SHEAR (VWS), WARM SEA SURFACE
TEMPERATURES (29-30 C), AND MODERATE OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: 171113Z METOP-B ASCAT SCATTEROMETER DATA.


CURRENT STEERING MECHANISM: NORTHEASTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED OVER EASTERN AUSTRALIA.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T4.0 - 65 KTS
   ABRF: T3.5 - 55 KTS
   CIMSS ADT: 57 KTS AT 171200Z
   CIMSS AIDT: 44 KTS AT 171200Z
   CIMSS D-PRINT: 44 KTS AT 171200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: PEAK INTENSITY HAS NOTABLY INCREASED
FROM THE PREVIOUS FORECAST. THE SYSTEM IS NOW FORECAST TO HAVE A
PEAK INTENSITY OF 115 KTS JUST PRIOR TO MAKING LANDFALL.

FORECAST DISCUSSION: TC NARELLE IS FORECAST TO TRACK WESTWARD
TOWARD THE CAPE YORK PENINSULA UNDER THE STEERING INFLUENCE OF A
STR CENTERED OVER EASTERN AUSTRALIA. A BRIEF WEST-SOUTHWESTWARD
MOTION IS EXPECTED BETWEEN TAU 12-36 AS A SHORTWAVE TROUGH WEAKENS
THE STR. AFTER TAU 36 THE SYSTEM IS FORECAST TO TRACK WITH A NEARLY
STRAIGHT WESTWARD TRAJECTORY AS A SECOND STR CENTERED OVER WESTERN
AUSTRALIA BECOMES THE PRIMARY STEERING MECHANISM. AN INITIAL
LANDFALL IS FORECAST TO OCCUR NEAR TAU 60 TO THE EAST OF COEN,
AUSTRALIA. TC NARELLE WILL EMERGE OVER THE GULF OF CARPENTARIA NEAR
TAU 72 AND CONTINUE TRACKING WESTWARD WITH A SECOND LANDFALL
FORECAST TO OCCUR NEAR TAU 96 IN THE VICINITY OF GROOTE EYLANDT.
AFTER TAU 96 THE SYSTEM WILL TRACK INLAND WITHIN THE TOP END AREA,
SOUTH OF DARWIN, THROUGH THE REMAINDER OF THE FORECAST PERIOD. IN
TERMS OF INTENSITY, TC NARELLE IS FORECAST TO UNDERGO RAPID
INTENSIFICATION (RI) OVER THE NEXT 48 HOURS TO A PEAK INTENSITY OF
AROUND 115 KTS IN RESPONSE TO THE FAVORABLE ENVIRONMENTAL
CONDITIONS. THE SYSTEM WILL THEN RAPIDLY WEAKEN OVER THE CAPE YORK
PENINSULA DUE TO TERRAIN INTERACTION. ONCE THE SYSTEM EMERGES IN
THE GULF OF CARPENTARIA WARM SEA SURFACE TEMPERATURES AND LOW VWS
WILL ALLOW FOR A PERIOD OF REINTENSIFICATION BEFORE MAKING ITS
SECOND LANDFALL. TC NARELLE WILL THEN WEAKEN AGAIN DUE TO TERRAIN
INTERACTION THROUGH TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN VERY GOOD
AGREEMENT THROUGH TAU 60 WITH THE EXCEPTION OF NAVGEM, WHICH TRACKS
THE SYSTEM SIGNIFICANTLY FARTHER SOUTH THAN THE REST OF THE
GUIDANCE. DISCOUNTING NAVGEM, THERE IS A 50 NM CROSS-TRACK SPREAD
AND 60 NM ALONG-TRACK SPREAD AT TAU 60. AFTER TAU 60, ALONG-TRACK
SPREAD BEGINS TO INCREASE WITH GFS BEING CONSIDERABLY SLOWER THAN
OTHER MODELS. THOUGH CROSS-TRACK SPREAD REMAINS LOW, ALONG-TRACK
SPREAD INCREASES TO AROUND 200 NM AT TAU 120. THE JTWC TRACK
FORECAST IS PLACED NEAR THE CONSENSUS AND GOOGLE DEEPMIND ENSEMBLE
MEAN, WITH HIGH CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE
THEREAFTER. INTENSITY GUIDANCE GENERALLY AGREES ON A RAPID OR
NEAR-RAPID INTENSIFICATION RATE THROUGH TAU 48. NEARLY EVERY
AVAILABLE RI AID HAS TRIGGERED THIS MODEL RUN. PEAK INTENSITIES
BETWEEN MESOSCALE MODELS ALL CONVERGE AROUND 115-125 KTS. THE JTWC
INTENSITY FORECAST IS IN LINE WITH THE MESOSCALE MODELS, CALLING
FOR A PEAK INTENSITY OF 115 KTS. AFTER TAU 48, MODELS AGREE ON
WEAKENING THROUGH TAU 72 FOLLOWED BY SLIGHT REINTENSIFICATION
THROUGH TAU 96 AND WEAKENING THROUGH TAU 120. THE JTWC INTENSITY
FORECAST IS PLACED WITH MEDIUM CONFIDENCE THROUGH TAU 72 AND LOW
CONFIDENCE THEREAFTER DUE TO INHERENT UNCERTAINTY IN THE REACTION
OF THE SYSTEM TO TERRAIN INFLUENCES. 

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