WDPS31 PGTW 170300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27P (TWENTYSEVEN) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.3S 156.6E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 685 NM EAST-NORTHEAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A 
CONSOLIDATING LOW LEVEL CIRCULATION CENTER (LLCC) WITH PERSISTENT 
DEEP CONVECTION IN THE NORTHEASTERN QUADRANT. THE LLCC WAS FULLY 
EXPOSED EARLIER IN THE DAY DUE TO MODERATE SOUTHWESTERLY SHEAR, BUT 
SUBSEQUENTLY TUCKED UNDER REDEVELOPING CONVECTION IN THE HOURS PRIOR 
TO 0000Z. A 162315Z ASCAT-C BULLSEYE REVEALED A WELL-DEFINED LLCC WITH 
A BAND OF 35-40KT WINDS WRAPPING AROUND THE EASTERN SEMI-CIRCLE AND
PROVIDING HIGH CONFIDENCE TO BOTH THE INITIAL POSITION AND
INTENSITY. ENVIRONMENTAL CONDITIONS ARE FAVORABLE FOR FURTHER 
INTENSIFICATION, CHARACTERIZED BY LOW DEEP-LAYER VERTICAL WIND SHEAR 
(VWS), WARM SSTS, MODERATE OHC AND ROBUST POLEWARD OUTFLOW INTO A 
DEEP
UPPER-LEVEL TROUGH PASSING TO THE SOUTH.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   ABRF: T2.0 - 30 KTS
   CIMSS D-PRINT: 29 KTS AT 170000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 27P IS FORECAST TO TRACK
WEST-SOUTHWESTWARD THROUGH THE DURATION OF THE PERIOD, ALONG THE 
NORTHERN PERIPHERY OF A SERIES OF SUBTROPICAL RIDGES (STR) SITUATED 
OVER AUSTRALIA. AS THE DEEP-LAYER TROUGH CURRENTLY SOUTH OF THE 
SYSTEM PROPAGATES OFF TO THE EAST; THE STEERING GRADIENT WILL 
TIGHTEN, ALLOWING TC 27P TO ACCELERATE AFTER TAU 12. BY TAU 48, A 
SECOND TROUGH WILL TRANSIT THE EASTERN COAST OF AUSTRALIA,
WEAKENING THE STR AXIS AND INDUCING A DECELERATION AS TC 27P
APPROACHES LANDFALL ALONG THE CAPE YORK PENINSULA, WHICH IS
EXPECTED TO OCCUR NEAR TAU 72. AS THE SYSTEM CROSSES THE CAPE YORK
PENINSULA, THE UPPER-LEVEL TROUGH EJECTS EASTWARD, AND A SECOND
STR DEVELOPS OVER CENTRAL AUSTRALIA IN ITS WAKE. TC 27P IS FORECAST 
TO ACCELERATE WESTWARD INTO THE GULF OF CARPENTARIA AFTER TAU 72, 
MAKING A SECOND LANDFALL ALONG THE WESTERN COAST OF THE GULF PRIOR TO 
TAU 96, THEN CONTINUING INLAND TO A POSITION SOUTHEAST OF DARWIN BY 
THE END OF THE FORECAST. THERE ARE SIGNIFICANT DISCREPANCIES IN TRACK 
SPEED AMONG THE MODEL GUIDANCE, WHICH WILL HAVE CORRESPONDING IMPACTS 
ON THE INTENSITY FORECAST. IN THE SHORT-TERM, THE SYSTEM IS CURRENTLY 
UNDERGOING VORTEX ALIGNMENT AND WILL EXHIBIT A MODEST INTENSIFICATION 
RATE OVER THE NEXT 12 TO 24 HOURS, GENERALLY FOLLOWING THE STANDARD 
T-NUMBER DEVELOPMENTAL CLIMATOLOGY. AFTER TAU 24, ONCE THE VORTEX 
ALIGNS, TC 27P WILL INTENSIFY AT A RAPID RATE BETWEEN TAU 24 AND 48 
AS SHEAR LESSENS AND THE SYSTEM PASSES OVER THE HIGH OCEAN HEAT 
CONTENT OF THE CORAL SEA. PEAK INTENSITY OF 90 KNOTS IS EXPECTED TO 
OCCUR COINCIDENT WITH LANDFALL. THE SYSTEM WILL WEAKEN SIGNIFICANTLY 
AS IT TRANSITS CAPE YORK, BUT UNDERGO RE-INTENSIFICATION IN THE GULF 
OF CARPENTARIA, ALTHOUGH MODERATE EASTERLY SHEAR WILL LIMIT THE 
MAGNITUDE OF RE-DEVELOPMENT. AFTER THE SECOND LANDFALL, TC 27P WILL 
RAPIDLY WEAKEN DUE TO LAND INTERACTION AND DRY AIR ENTRAINMENT. THE 
ULTIMATE INTENSITY OF TC 27P WILL BE HIGHLY DEPENDENT UPON THE TRACK 
SPEED, WITH A SLOWER SPEED EQUATING TO A HIGHER PEAK INTENSITY. 
LANDFALL TIMING REMAINS HIGHLY UNCERTAIN, WITH THE FORECAST HEDGED ON 
THE EARLIER SIDE CURRENTLY. 

MODEL DISCUSSION: DETERMINISTIC, ENSEMBLE AND ARTIFICIAL
INTELLIGENCE (AI) TRACK GUIDANCE IS IN STRONG AGREEMENT WITH THE
OVERALL TRACK DIRECTION, WITH CROSS-TRACK SPREAD INCREASING TO
APPROXIMATELY 150NM BY TAU 120. THE GALWEM AND EGRR ARE NORTHERN 
OUTLIERS FROM THE REMAINDER OF THE GUIDANCE PACKAGE, WITH THE SYSTEM
TRACKING TOWARD THE LATITUDE OF WEIPA. THE REMAINDER OF THE GUIDANCE 
PACKAGE IS TIGHTLY CONFINED NEAR THE CONSENSUS MEAN. HOWEVER, ALONG-
TRACK SPREAD IS MUCH HIGHER, EMERGING AS EARLY AS TAU 36, INCREASING 
TO 215NM AT TAU 72 BETWEEN THE FAST-BIASED ECMWF AND SLOW-BIASED GFS. 
ALONG-TRACK UNCERTAINTY CONTINUES TO INCREASE TO 400NM BETWEEN THE 
OUTLIERS BY THE END OF THE FORECAST PERIOD. THE JTWC FORECAST IS 
HEDGED TOWARDS THE FASTER SIDE OF THE GUIDANCE, CLOSE TO THE MULTI-
MODEL CONSENSUS MEAN, WITH MEDIUM CONFIDENCE TRENDING TO LOW 
CONFIDENCE IN THE EXTENDED FORECAST. INTENSITY GUIDANCE IS ALSO 
HIGHLY UNCERTAIN, BOTH IN THE TIMING AND MAGNITUDE OF THE PEAK 
INTENSITY. THE FASTER MODELS SUCH AS ECMWF AND HWRF SHOW A LOWER PEAK 
INTENSITY AT LANDFALL BUT HIGHER POTENTIAL IN THE GULF OF 
CARPENTARIA. THE SLOWER MODELS SUCH AS GFS DEPICT A STRONGER SYSTEM 
AT LANDFALL AND A WEAKER ONE IN THE GULF. THE JTWC FORECAST IS 
ROUGHLY CONSISTENT WITH THE CONSENSUS, HEDGED TOWARDS THE HIGHER END 
OF THE GUIDANCE THROUGH THE FORECAST PERIOD.  

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