WDXS31 PGTW 060900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (TWENTY) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.8S 120.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 92 NM SOUTHWEST OF BROOME, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 20S WITH A PARTIALLY OBSCURED LOW-LEVEL CIRCULATION
CENTER (LLCC) AS FLARING AND WIDESPREAD CONVECTION HAS CONTINUED
THROUGHOUT THE SYSTEMS NORTHERN AND WESTERN QUADRANTS. LOW-LEVEL
CURVED CLOUD LINES CAN BE OBSERVED ON ANIMATED MSI WRAPPING JUST
BENEATH THE PRIMARY CONVECTIVE STRUCTURE IN CLOSE PROXIMITY TO THE
LLCC, SOUTHWEST OF BROOME. THE ENVIRONMENT REMAINS LARGELY
FAVORABLE FOR CONTINUED INTENSIFICATION, WITH VERY WARM SEA SURFACE
TEMPERATURES BETWEEN 30-31 C, MINIMAL VERTICAL WIND SHEAR (VWS) OF
LESS THAN 5 KTS, AND ROBUST POLEWARD AND EQUATORWARD OUTFLOW ALOFT.
THE INITIAL POSITION HAS BEEN PLACED WITH MEDIUM CONFIDENCE BASED
ON ANIMATED MSI. THE INITIAL INTENSITY HAS BEEN ASSESSED WITH
MEDIUM CONFIDENCE BASED ON SUBJECTIVE AGENCY INTENSITY ESTIMATES
AND CIMSS OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: COMPETING STEERING FLOWS BETWEEN A
SUBTROPICAL RIDGE CENTERED IN EASTERN AUSTRALIA AND AN ADDITIONAL
SUBTROPICAL RIDGE LOCATED TO THE SOUTHWEST IN THE SOUTHEASTERN
INDIAN OCEAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   APRF: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 060530Z
   CIMSS AIDT: 30 KTS AT 060530Z
   CIMSS D-MINT: 35 KTS AT 060555Z
   CIMSS D-PRINT: 41 KTS AT 060610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: A SOUTHWESTWARD TRACK OVER THE LAST
FEW HOURS HAS CHANGED THE FORECAST TRACK TO REMAIN RELATIVELY
CLOSER TO AUSTRALIA’S NORTHWEST COASTLINE, MAKING LANDFALL NEAR TAU
36 SOUTHWEST OF DAMPIER. 

FORECAST DISCUSSION: TC 20S IS FORECASTED TO CONTINUE TRACKING
SOUTHWESTWARD THROUGH TAU 36, ALONG THE WESTERN PERIPHERY OF A
WEAKENING SUBTROPICAL RIDGE CENTERED OVER EASTERN AUSTRALIA. NEAR
TAU 36, TC 20S WILL BEGIN TO ROUND THE SUBTROPICAL RIDGE AXIS WHILE
A SEGMENT OF THE DEEP-LAYER STEERING RIDGE MEANDERS TO THE
SOUTHEAST OF THE CYCLONE. AS THE SUBTROPICAL RIDGE RETREATS TO THE
EAST AND SOUTHEAST DURING THE SAME WINDOW, TC 20S IS FORECASTED TO
TRACK SOUTHWARD UNTIL JUST AFTER TAU 48. FOLLOWING TAU 48, TC 20S IS 
FORECASTED TO CONTINUE ROUNDING THE WESTERN MOST EXTENT
OF THE RIDGE AXIS, GAINING A SOUTH-SOUTHEASTWARD TRACK UNTIL
COMPLETE DISSIPATION OVER LAND AT TAU 72. REGARDING INTENSITY, LOW
VERTICAL WIND SHEAR OF LESS THAN 10 KTS, ROBUST POLEWARD OUTFLOW,
AND WARM COASTAL WATERS BETWEEN 29-30 C WILL ALLOW FOR QUICK
INTENSIFICATION TOWARD 75 KTS BY TAU 36, JUST BEFORE LANDFALL.
FOLLOWING TAU 36, TOPOGRAPHICAL INTERACTION, STEADILY INCREASING
VERTICAL WIND SHEAR TO NEAR 20 KTS, AND DRY-AIR ENTRAINMENT
WRAPPING AROUND THE SYSTEMS NORTHERN SEMICIRCLE INTO TAU 72 WILL
ERODE THE SURFACE VORTEX. TC 20S IS FORECASTED TO GRADUALLY WEAKEN
BETWEEN TAU 36 AND TAU 72, DECAYING TO 35 KTS NEAR KENNEDY RANGE
NATIONAL PARK BY THE END OF THE FORECAST PERIOD.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE AND ARTIFICIAL
INTELLIGENCE (AI) SOLUTIONS ARE IN TIGHT AGREEMENT THROUGH THE NEXT
36 HOURS INTO LANDFALL, WITH A 39 NM CROSS-TRACK. FOLLOWING TAU 36, 
JTWC TRACK CONSENSUS MEMBERS BEGIN TO ILLUSTRATE A PICTURE OF SLIGHT 
DIVERGENCE, WITH AN INCREASING CROSS-TRACK SPREAD TO 62 NM BY TAU 48. 
BY TAU 72, THE CROSS-TRACK SPREAD CONTINUES TO INCREASE TOWARD 127 NM, 
WITH NAVGEM CHARACTERIZING THE WESTERN-MOST TRACK TOWARD LAKE MACLEOD, 
HOWEVER, ALL CURRENT JTWC TRACK CONSENSUS MEMBERS SHOW THE ROUNDING OF 
THE STR AXIS NEAR TAU 48 EAST OF LEARMONTH AND OVER LAND. THE JTWC 
TRACK FORECAST HAS BEEN PLACED WITH MEDIUM CONFIDENCE, AND ALIGNED 
CLOSELY TO THE JTWC MULTI-MODEL CONSENSUS, RELIABLE DETERMINISTIC 
MEMBERS, AND AI SOLUTIONS. REGARDING INTENSITY, ALL JTWC INTENSITY 
CONSENSUS MEMBERS ILLUSTRATE A SHARP INTENSIFICATION PHASE THROUGH TAU 
24, STEADY INTENSITIES BETWEEN TAU 24 AND TAU 36, AND A RAPID 
WEAKENING PHASE THEREAFTER DUE TO LAND INTERACTION. THE JTWC INTENSITY 
FORECAST HAS BEEN ASSESSED WITH MEDIUM CONFIDENCE AND PLACED JUST 
ABOVE THE MULTI-MODEL CONSENSUS UNTIL TAU 36, THEN ALIGNED WITH THE 
MULTI-MODEL CONSENSUS THROUGH THE TERMINAL WEAKENING PHASE UNTIL TAU 
72. 

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