WDXS31 PGTW 080900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (MITCHELL) WARNING 
NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.3S 114.6E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 66 NM NORTH-NORTHEAST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AFTER REACHING PEAK INTENSITY APPROXIMATELY 18 HOURS AGO, TROPICAL
CYCLONE (TC) 20S (MITCHELL) HAS STEADILY WEAKENED AS IT HAS
TRAVERSED SOUTHWESTWARD PARALLEL TO THE NORTHWESTERN AUSTRALIAN
COASTLINE. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
REDEVELOPING CENTRAL DENSE OVERCAST (CDO) FEATURE, WITH DEEP
CONVECTION WRAPPING UPSHEAR AND ONCE AGAIN OBSCURING THE LOW LEVEL
CIRCULATION CENTER (LLCC). ANIMATED RADAR IMAGERY FROM LEARMONTH 
DEPICTS A RELATIVELY BROAD AND ILL-DEFINED EYE FEATURE WHICH REMAINS 
OPEN ON THE EASTERN, UPSHEAR QUADRANT. DRY LOW-LEVEL AIR ADVECTING 
OFFSHORE IS ALSO PENETRATING THE INNER-CORE FROM THE EAST, 
CONTRIBUTING TO THE ERODED EYEWALL STRUCTURE ON THE EASTERN FLANK OF 
THE SYSTEM. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE 
BASED ON GROUND-BASED RADAR IMAGERY. THE INITIAL INTENSITY IS 
ASSESSED WITH MEDIUM CONFIDENCE BASED ON A CONSENSUS OF THE 
SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED BELOW. 
ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE. WHILE VERTICAL 
WIND SHEAR (VWS) REMAINS IN THE LOW RANGE (10-15 KNOTS), MID-LEVEL 
SHEAR, AS ESTIMATED FROM HIGH-RESOLUTION MODELS AND EXTRAPOLATED FROM 
THE BROOME UPPER-AIR DATA, IS IN THE MODERATE TO HIGH RANGE (25-30 
KNOTS). THEREFORE, WHILE SSTS REMAIN CONDUCIVE AND OUTFLOW ALOFT IS 
STRONGLY DIVERGENT, THE SYSTEM IS STRUGGLING TO MAINTAIN A VERTICALLY 
ALIGNED AND AXISYMMETRIC VORTEX.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) OVER CENTRAL AUSTRALIA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   DEMS: T4.5 - 77 KTS
   APRF: T4.0 - 65 KTS
   CIMSS SATCON: 72 KTS AT 080530Z
   CIMSS ADT: 69 KTS AT 080530Z
   CIMSS AIDT: 72 KTS AT 080530Z
   CIMSS D-MINT: 72 KTS AT 080607Z
   CIMSS D-PRINT: 60 KTS AT 080600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY LOW- TO MID-LEVEL AIR ALONG THE EASTERN AND
NORTHERN FLANKS. MODERATE MID-LEVEL NORTHEASTERLY SHEAR. 

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 20S HAS TRACKED SOUTHWESTWARD THROUGHOUT
THE DAY, PASSING OVER OR JUST NORTH OF BARROW ISLAND SHORTLY AFTER
THE 0000Z HOUR AND CONTINUING TOWARDS THE EXMOUTH PENINSULA. THE
STEERING RIDGE TO THE EAST HAS EXTENDED FURTHER WEST THAN ORIGINALLY
ANTICIPATED, RESULTING IN A TRACK WHICH REACHES FURTHER WEST BEFORE
RECURVING SOUTHWARD. THE CURRENT FORECAST ESTIMATES LANDFALL
OCCURRING WITHIN THE NEXT FEW HOURS ALONG THE NORTHWEST CAPE AREA,
WITH THE VORTEX CENTER TRANSITING DOWN THE WESTERN COAST OF THE 
EXMOUTH PENINSULA AND BRIEFLY RE-EMERGING OVER WATER TO THE WEST OF 
CORAL BAY. THE SYSTEM WILL DECELERATE SLIGHTLY OVER THE NEXT 12 HOURS 
AS IT APPROACHES THE RIDGE AXIS. THE SYSTEM ROUNDS THE RIDGE BY TAU 
24, THEN ACCELERATES SOUTHEASTWARD ALONG THE GRADIENT BETWEEN THE STR 
OVER AUSTRALIA AND AN APPROACHING UPPER-LEVEL TROUGH MOVING IN FROM 
THE SOUTHWEST. REGARDING INTENSITY, TC 20S IS SLOWLY BUT STEADILY
WEAKENING UNDER MARGINAL CONDITIONS AS IT APPROACHES LANDFALL. HE 
RECENT PULSATION OF DEEP CONVECTION, WHICH IS WRAPPING UPSHEAR, 
SUGGESTS THAT THE SYSTEM LIKELY WILL MAINTAIN STEADY-STATE INTENSITY 
THROUGH LANDFALL, BEFORE THE ONSET OF MORE RAPID CYCLOLYSIS AS IT 
TURNS SOUTHWARD. WHILE THE LLCC MAY TEMPORARILY MOVE BACK OVER WATER, 
ITS PROXIMITY TO LAND, INCREASING VWS, AND ENHANCED DRY AIR 
ENTRAINMENT OFF THE CONTINENT WILL INHIBIT RE-INTENSIFICATION, AND 
THE SYSTEM WILL RAPIDLY WEAKEN AFTER TAU 12. AS THE SYSTEM MOVES 
INLAND PERMANENTLY AFTER TAU 24, IT WILL CONTINUE TO RAPIDLY WEAKEN 
DUE TO SURFACE FRICTION, DRY AIR ENTRAINMENT, AND DRAMATICALLY HIGHER 
SHEAR VALUES, DISSIPATING OVER WESTERN AUSTRALIA BY TAU 48.

MODEL DISCUSSION: DETERMINISTIC, ENSEMBLE, AND ARTIFICIAL
INTELLIGENCE (AI) MODELS ARE IN TIGHT AGREEMENT ON THE OVERALL
TRACK SCENARIO, WITH MINIMAL CROSS- OR ALONG-TRACK SPREAD. THE 
WESTERNMOST OF THE TRACKERS (EGRR) TAKES THE SYSTEM APPROXIMATELY 
12NM OFF THE WESTERN COAST, WHILE THE EASTERNMOST TRACKER (ECMWF) 
KEEPS THE SYSTEM APPROXIMATELY 10NM INLAND AS IT ROUNDS THE RIDGE 
AXIS; ALL MODEL TRACKERS KEEP THE SYSTEM EAST OF SHARK BAY. THE JTWC 
FORECAST IS POSITIONED CONSISTENT WITH THE AI CONSENSUS MEAN, 
COINCIDENT WITH THE CENTER OF THE GUIDANCE ENVELOPE, WITH HIGH 
CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN TIGHT AGREEMENT, WITH ALL 
AVAILABLE MODELS INDICATING STEADY TO RAPID WEAKENING AB INITIO, 
CONTINUING THROUGH DISSIPATION. THE JTWC FORECAST IS ALIGNED WITH THE 
HAFS-A MODEL TREND LINE WITH HIGH CONFIDENCE. 

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