WDPS31 PGTW 200900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (NARELLE) WARNING 
NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.4S 142.0E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 304 NM NORTHWEST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 27P (NARELLE) QUICKLY TRACKING WESTWARD ACROSS
NORTHERN QUEENSLAND, AUSTRALIA WITH A RAPIDLY DISSIPATING
CONVECTIVE STRUCTURE FULLY OBSCURING THE LOW-LEVEL CIRCULATION
CENTER (LLCC). THE ENVIRONMENTAL ANALYSIS CHARACTERIZES A
SHORT-TERM UNFAVORABLE PHASE DRIVEN PRIMARILY FROM PERSISTENT LAND
INTERACTION AND UNFAVORABLE VERTICAL WIND SHEAR (VWS) OVER 25 KTS.
THE INITIAL POSITION HAS BEEN PLACED WITH HIGH CONFIDENCE BASED ON
ANIMATED MSI AND WEIPA, AUSTRALIA RADAR IMAGERY. THE INITIAL
INTENSITY HAS BEEN ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
ONGOING AND EXPECTED RAPID WEAKENING PHASE DUE TO INCREASED VWS AND
LAND INTERACTION. OVER THE NEXT FEW HOURS, TC 27P WILL REEMERGE
OVER THE EASTERN GULF OF CARPENTARIA, INTRODUCING AN IMPROVED
ENVIRONMENT WITH WARM SEA SURFACE TEMPERATURES OF 29-30 C AND
SUPPORTIVE OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: PERSISTENCE OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: NORTHEASTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE CENTERED TO THE SOUTHWEST, OVER WESTERN AUSTRALIA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   CIMSS ADT: 87 KTS AT 200530Z
   CIMSS AIDT: 87 KTS AT 200530Z
   CIMSS D-MINT: 93 KTS AT 200429Z
   CIMSS D-PRINT: 72 KTS AT 200600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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: TC 27P IS FORECASTED TO CONTINUE TRACKING
WESTWARD ALONG THE NORTHERN PERIPHERY OF THE DEEP-LAYER STR
CENTERED OVER WESTERN AUSTRALIA UNTIL TAU 48. FOLLOWING TAU 48, A
WESTWARD EXTENSION OF THE STR TO THE SOUTHWEST IS EXPECTED TO
WEAKEN AND RETREAT SLIGHTLY EASTWARD, ALLOWING TC NARELLE TO BEGIN
A MOSTLY WEST-SOUTHWESTWARD TRACK THROUGHOUT THE REMAINDER OF THE
FORECAST PERIOD. REGARDING INTENSITY, TC 27P IS EXPECTED TO
REEMERGE OVER WARM SEA SURFACE TEMPERATURES IN THE EASTERN GULF OF
CARPENTARIA OVER THE NEXT FEW HOURS, SLOWING THE RAPID WEAKENING
PHASE. AT THIS TIME, THE LLCC IS EXPECTED TO REMAIN RELATIVELY
BROAD WHILE SURFACE INTENSITIES GRADUALLY DECAY TOWARD 85 KTS BY
TAU 24 DUE TO UNFAVORABLE VWS EXCEEDING 25 KTS. AS TC 27P TRACKS
WESTWARD, A SECONDARY LANDFALL ALONG THE EAST COAST OF THE NORTHERN
TERRITORY IS FORECASTED, ERODING THE SURFACE VORTEX TO 75 KTS BY
TAU 36. AS TC NARELLE TRACKS WESTWARD ACROSS THE NORTHERN
TERRITORY, FURTHER WEAKENING IS EXPECTED, DECAYING INTENSITIES TO
55-60 KTS BEFORE REEMERGING OVER THE JOSEPH BONAPARTE GULF BETWEEN
TAU 48 AND TAU 72. AFTER THE BRIEF TRANSIT OVER OPEN WATER, A THIRD
LANDFALL IS FORECASTED IN THE NORTHERN EXTENT OF WESTERN AUSTRALIA,
FURTHER WEAKENING SURFACE INTENSITIES TO 50-55 KTS BETWEEN TAU 72
AND TAU 96. PRIOR TO TAU 96, THE SYSTEM WILL ONCE AGAIN REEMERGE
OVER OPEN WATER, IN THE TIMOR SEA, AND START TO GRADUALLY INTENSIFY
TOWARD 70 KTS BY THE END OF THE FORECAST PERIOD AS ENVIRONMENTAL
CONDITIONS BECOME MOSTLY FAVORABLE. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE CONTINUES TO BE IN
VERY STRONG AGREEMENT THROUGHOUT THE ENTIRETY OF THE FORECAST
PERIOD, EXHIBITING A CROSS-TRACK SPREAD OF 43 NM BY TAU 72,
GRADUALLY INCREASING TO 128 NM BY TAU 120. THE ALONG-TRACK SPREAD
BEGINS TO INCREASE DURING THE LATER TAUS IN THE FORECAST DUE TO
INTERMITTENT LAND INTERACTION THROUGHOUT THE SYSTEMS WESTWARD
TRACK; HOWEVER, ALL GUIDANCE REMAINS WITHIN A 200 NM ENVELOPE.
THEREFORE, THE JTWC TRACK FORECAST HAS BEEN PLACED WITH HIGH
CONFIDENCE THROUGHOUT THE INITIAL 72 HOURS, AND MEDIUM CONFIDENCE
THEREAFTER. REGARDING INTENSITY, THE JTWC INTENSITY FORECAST HAS
BEEN ALIGNED CLOSELY TO THE JTWC MULTI-MODEL CONSENSUS THROUGHOUT
THE FORECAST PERIOD WITH MEDIUM CONFIDENCE. NOTABLY, THE GFS
DETERMINISTIC SOLUTION CONTINUES TO ILLUSTRATE A RAPID WEAKENING
PHASE THROUGHOUT THE NEXT 12 HOURS, WITH STEADY INTENSITIES NEAR 45
KTS THEREAFTER, CONTINUING AS THE ONLY OUTLIER. 

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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