WDPS31 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.3S 139.6E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 511 NM EAST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 27P RECONSOLIDATING, WITH EXPANDING DEEP CONVECTION
ALONG THE NORTHERN SEMICIRCLE AND BANDING DEEP CONVECTION BEGINNING
TO REWRAP AROUND THE WESTERN SEMICIRCLE. A 201616Z AMSR2 WINDSPEED
IMAGE REVEALS THE HIGHEST WINDS ARE CONFINED TO THE NORTHERN
SEMICIRCLE, DISPLAYING 55-65KTS OUTSIDE THE RAIN CONTAMINATED
REGION. A 201837Z GMI PASS REVEALS THE LOW LEVEL CIRCULATION CENTER
(LLCC) REMAINS BROAD AND ELONGATED WITH A SLIGHT VERTICAL TILT TO
THE WEST. ENVIRONMENTAL ANALYSIS INDICATES A MARGINALLY FAVORABLE
ENVIRONMENT, CHARACTERIZED BY WARM (29-30 C) SEA SURFACE
TEMPERATURES AND A STRONG EQUATORWARD OUTFLOW CHANNEL, OFFSET BY
LOW TO MODERATE (15-20 KTS) EASTERLY VERTICAL WIND SHEAR (VWS). THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
AFOREMENTIONED 201837Z GMI IMAGE. THE INITIAL INTENSITY OF 65 KTS IS
ASSESSED WITH LOW CONFIDENCE BASED ON THE LARGE SPREAD IN
INTENSITIES REPRESENTED BY THE CIMSS ESTIMATES AND AGENCY OBJECTIVE
DVORAK FIXES LISTED BELOW, AND THE ASMR2 WINDSPEED DATA FROM
201616Z.

INITIAL WIND RADII BASIS: A 201616Z AMSR2 WINDSPEED IMAGE

CURRENT STEERING MECHANISM: THE NORTHEASTERN PERIPHERY OF A
SUBTROPICAL RIDGE CENTERED OVER WESTERN AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T4.0 - 65 KTS
   ABRF: T3.0 - 45 KTS
   CIMSS SATCON: 67 KTS AT 201730Z
   CIMSS ADT: 72 KTS AT 201900Z
   CIMSS AIDT: 63 KTS AT 201900Z
   CIMSS D-MINT: 50 KTS AT 201618Z
   CIMSS D-PRINT: 43 KTS AT 201900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: LOW
   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 (NARELLE) IS FORECAST TO MAINTAIN ITS
WESTWARD TRACK FOR THE NEXT 24 HOURS AS IT REMAINS ON THE
NORTHEASTERN PERIPHERY OF THE STEERING STR CENTERED OVER WESTERN
AUSTRALIA. BEGINNING AROUND TAU 24, THE RIDGE IS EXPECTED TO SHIFT
EASTWARD AND INDUCE A WEST-SOUTHWESTWARD TRACK FROM TAU 24-72.
AROUND TAU 72, 27P IS FORECAST TO TURN SOUTHWESTWARD INTO A
WEAKNESS IN THE STR NOW CENTERED OVER CENTRAL AUSTRALIA, RESULTING
IN A SOUTHWESTWARD TRACK FROM TAU 72 UNTIL THE END OF THE FORECAST
PERIOD. REGARDING INTENSITY, 27P IS FORECAST TO INTENSIFY SLIGHTLY
WITHIN THE GULF OF CARPENTARIA, INHIBITED BY MID-LEVEL VWS AND
NARELLE'S INTERNAL STRUCTURE. LANDFALL IS ANTICIPATED TO OCCUR JUST
PRIOR TO TAU 24, CAUSING 27P TO WEAKEN STEADILY AS IT SPENDS THE
NEXT 48 HOURS OVER LAND. NARELLE IS FORECAST TO REEMERGE BRIEFLY
OVER WATER WITHIN THE JOSEPH BONAPARTE GULF BETWEEN TAU 48-72, BUT
IS NOT EXPECTED TO SIGNIFICANTLY INTENSIFY DURING THIS TIME. THE
STORM IS ANTICIPATED TO EMERGE OVER THE TIMOR SEA NEAR TAU 72,
ALLOWING REINTENSIFICATION THROUGH THE END OF THE FORECAST. THE
LIMITING FACTOR FOR INTENSIFICATION IN THE TIMOR SEA IS MID-LEVEL
VWS IN AN OTHERWISE FAVORABLE ENVIRONMENT, INDICATING THE
POSSIBILITY OF HIGHER INTENSITIES AT THE END OF THE FORECAST PERIOD
SHOULD THE VWS BE LOWER THAN FORECAST.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE REMAINS IS
GOOD AGREEMENT THROUGH TAU 72, WITH MINOR DISCREPANCIES IN BOTH
CROSS-TRACK AND ALONG-TRACK SPREAD. AROUND TAU 72, THE AI TRACK
MODELS DIVERGE FROM THE TRADITIONAL GLOBAL AND MESOSCALE MODELS AND
ASSUME A SOUTHWESTWARD TRACK, WHILE THE REMAINING MODELS CONTINUE
ON A WEST-SOUTHWESTWARD TRACK, RESULTING IN A CROSS-TRACK SPREAD OF
ROUGHLY 200NM AT TAU 120. THE JTWC FORECAST TRACK IN PLACED CLOSE
TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE THROUGH TAU 72
AND MEDIUM CONFIDENCE FROM TAU 72 THROUGH THE END OF THE FORECAST
PERIOD. REGARDING INTENSITY, RELIABLE INTENSITY AIDS ARE IN GOOD
AGREEMENT IN INTENSIFICATION WHILE 27P IS WITHIN THE GULF OF
CARPENTARIA, FOLLOWED BY SIGNIFICANT WEAKENING AFTER LANDFALL JUST
BEFORE TAU 24 UNTIL 27P REEMERGES OVER THE TIMOR SEA. THERE IS A
SLIGHT DISCREPANCY IN THE RATE OF INTENSIFICATION ONCE 27P IS BACK
OVER WATER IN THE TIMOR SEA, INJECTING UNCERTAINTY INTO THE JTWC
INTENSITY FORECAST AT THE END OF THE FORECAST PERIOD. AS A RESULT,
THE JTWC INTENSITY FORECAST IS ASSESSED WITH HIGH CONFIDENCE FROM
TAU 0-72 AND MEDIUM CONFIDENCE FROM TAU 72-120, AND IS ALIGNED
SLIGHTLY HIGHER THAN THE MULTI-MODEL CONSENSUS.

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