WDXS32 PGTW 251500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 15S (FIFTEEN) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.8S 127.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 182 NM WEST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TC 15S HAS CONSOLIDATED AND INTENSIFIED OVER THE PAST TWELVE HOURS
WHILE REMAINING BASICALLY QUASI-STATIONARY IN THE JOSEPH BONAPARTE
GULF. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
AN OBSCURED LOW LEVEL CIRCULATION (LLC) WITH A REGION OF DEEP, COLD
CONVECTION WITH A TAIL SHEARING OFF TOWARDS THE WEST UNDER MODERATE
EASTERLY SHEAR. THE INITIAL POSITION WAS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON ANALYSIS OF THE WYNDHAM RADAR WHICH SHOWED A
WEAK LIKELY MID-LEVEL ROTATION WITH A WELL DEFINED BAND OF
CYCLONICALLY CURVED CONVECTION STRETCHING ACROSS THE JOSEPH
BONAPARTE GULF. THE INITIAL INTENSITY OF 35 KNOTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE MULTI-AGENCY DVORAK CURRENT
INTENSITY ESTIMATES OF T2.5 FROM PGTW, KNES AND ADRM. THE SYSTEM IS
DRIFTING RATHER AIMLESSLY IN A WEAK STEERING PATTERN, TRAPPED
BETWEEN A DEEP SUBTROPICAL RIDGE TO THE SOUTH AND NEAR-EQUATORIAL
RIDGE (NER) TO THE NORTH. ENVIRONMENTAL ANALYSIS REVEALS MARGINALLY
FAVORABLE CONDITIONS OF VERY WARM SSTS AND GOOD POLEWARD OUTFLOW
OFFSET BY MODERATE EASTERLY SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   ADRM: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: PROXIMITY TO LAND. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 15S HAS STEADILY CONSOLIDATED AND
INTENSIFIED OVER THE PAST DAY WHILE REMAINING QUASI-STATIONARY IN
THE JOSEPH BONAPARTE GULF UNDER THE INFLUENCE OF A WEAK STEERING
PATTERN. THE SYSTEM IS EXPECTED TO DRIFT GENERALLY SOUTHWESTWARD
OVER THE NEXT 48 HOURS THOUGH THE EXACT TRACK IS UNCERTAIN AS THE
STEERING REGIME IS EXPECTED TO REMAIN WEAK FOR THE NEXT COUPLE OF
DAYS. AFTER TAU 48 THE SUBTROPICAL RIDGE (STR) TO THE SOUTH IS
FORECAST TO BUILD, WHICH WILL ALLOW FOR TC 15S TO MOVE OUT TOWARDS
THE SOUTHWEST, STRADDLING THE KIMBERLY COAST THROUGH THE REMAINDER
OF THE FORECAST PERIOD. THE EASTERLY SHEAR, CURRENTLY RUNNING
AROUND 10-15 KNOTS IS EXPECTED TO RELAX SLIGHTLY, THOUGH TC 15S
WILL CONTINUE TO STRUGGLE TO OVERCOME THIS SHEAR, LEADING TO SLOW
BUT STEADY INTENSIFICATION TO A PEAK OF 50 KNOTS PRIOR TO LANDFALL
NEAR CAPE LONDONDERRY. INCREASING SHEAR AND DISRUPTION OF THE LOW
LEVEL CORE DUE TO LAND INTERACTION WITH WEAKEN THE SYSTEM AS IT
TRANSITS ALONG THE COASTLINE THROUGH THE REMAINDER OF THE FORECAST.
WHILE THE MAJORITY OF THE GUIDANCE SUPPORTS THE JTWC FORECAST, THE
GFS AND GFS ENSEMBLE MEAN SUGGEST A WESTWARD TRACK OVER OPEN WATERS
UNDER THE INFLUENCE OF A STRONGER STR TO THE SOUTH. THIS ALTERNATE
SCENARIO WOULD ALLOW FOR A LONGER PERIOD OVER VERY WARM WATERS,
WITH A HIGHER PEAK INTENSITY. 

MODEL DISCUSSION: TRACK GUIDANCE SHOWS A HIGH DEGREE OF
UNCERTAINTY, WITH SOME MODELS SUGGESTING A LOOPING TRACK BACK TO
THE NORTH (GFS ENSEMBLE), SOME INDICATING AN EASTWARD TRACK (NVGM)
AND OTHERS INDICATING A WESTWARD TRACK (GFS). THE REMAINDER OF THE
PACKAGE IS GROUPED NEAR THE TES1 CONSENSUS MEAN AND SUPPORTS THE
JTWC TRACK. HOWEVER, IN LIGHT OF THE HIGH VARIANCE IN THE GUIDANCE
AND THE POTENTIAL FOR AN ALTERNATE SCENARIO AS DISCUSSED ABOVE,
THERE IS LOW CONFIDENCE IN THE JTWC FORECAST. INTENSITY GUIDANCE IS
A BIT BETTER BEHAVED, WITH ALL MEMBERS INDICATING INTENSIFICATION
TO A PEAK BETWEEN 40-50 KNOTS WITH THE EXCEPTION OF DECAY SHIPS
WHICH PREDICTS A PEAK NEAR 60 KNOTS. OF NOTE THE RIPA AID HAS BEEN
TRIGGERED, PREDICTING A PEAK OF 60 KNOTS BY TAU 24, BUT THIS IS
UNLIKELY IN THE FACE OF THE MODERATE SHEAR AND PROXIMITY TO LAND.
THE JTWC FORECAST LIES WITHIN THE TIGHT MODEL CLUSTER PEAKING AT 50
KNOTS WITH MEDIUM CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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