WDXS31 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (MITCHELL) WARNING 
NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.5S 113.4E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 138 NM SOUTH-SOUTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI), SURFACE OBSERVATIONS, 
AND METEOROLOGICAL RADAR IMAGERY INDICATE THAT TROPICAL CYCLONE (TC) 
20S IS TRANSITING ALONG THE LITTORAL REGION OF WESTERN AUSTRALIA, 
NORTH OF CARNARVON. RECENT RADAR DATA SUGGESTS THE SYSTEM HAS TURNED 
SOUTHEASTWARD AND THAT IT IS GENERALLY PARALLELING THE COAST TOWARDS 
SHARK BAY. SURFACE WINDS AT CARNARVON REMAIN EASTERLY, CONSTRAINING 
THE LOW-LEVEL CIRCULATION CENTER (LLCC) TO THE NORTH OF THE STATION. 
HOWEVER, A RAPID SHIFT SHOULD BEGIN SHORTLY AS THE LLCC PASSES VERY 
CLOSE TO THE STATION IN THE NEXT HOUR. THE INITIAL INTENSITY IS 
ASSESSED WITH MEDIUM CONFIDENCE, WEIGHTED TOWARDS THE UPPER QUARTILE 
OF OBJECTIVE INTENSITY ESTIMATES. ENVIRONMENTAL CONDITIONS ARE 
DEGRADED AS THE SYSTEM ACCELERATES SOUTHEASTWARD. SEA SURFACE 
TEMPERATURES (SSTS) ARE NOW SUB-26C, AND LAND MASS PROXIMITY IS 
INDUCING FRICTIONAL ATTENUATION AND ENTRAINMENT OF ADIABATICALLY DRY 
CONTINENTAL AIR FROM THE EAST, WHILE VERTICAL WIND SHEAR (VWS) IS 
RAPIDLY INCREASING.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: GRADIENT BETWEEN A MID-LEVEL
SUBTROPICAL RIDGE (STR) OVER CENTRAL AUSTRALIA AND A MID- TO
UPPER-LEVEL TROUGH TO THE SOUTHWEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   DEMS: T3.0 - 45 KTS
   APRF: T3.0 - 45 KTS
   CIMSS SATCON: 54 KTS AT 090548Z
   CIMSS ADT: 51 KTS AT 090630Z
   CIMSS AIDT: 43 KTS AT 090630Z
   CIMSS D-MINT: 45 KTS AT 090548Z
   CIMSS D-PRINT: 52 KTS AT 090600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: TERRAIN INTERACTION, ENTRAINMENT OF DRY MID-LEVEL
CONTINENTAL AIR INTO THE CORE FROM THE EAST. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST IS TRUNCATED TO 24
HOURS. 

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 20S (MITCHELL) HAS 
RECURVED AROUND THE STR AXIS AND IS NOW ACCELERATING SOUTHEASTWARD 
ALONG THE STEEPENING PRESSURE GRADIENT BETWEEN THE STR OVER CENTRAL 
AUSTRALIA AND AN APPROACHING BAROCLINIC UPPER-LEVEL TROUGH TO THE 
SOUTHWEST. THE SYSTEM IS FORECAST TO TRACK ALONG THE EASTERN 
PERIPHERY OF SHARK BAY, WITH LANDFALL ANTICIPATED AT THE SOUTHERN 
TERMINUS OF THE BAY WITHIN THE NEXT 12 HOURS. THE SYSTEM WILL 
SUBSEQUENTLY TRAVERSE FURTHER INLAND THROUGH THE REMAINDER OF THE 
FORECAST PERIOD. REGARDING INTENSITY, THE SYSTEM WILL CONTINUE TO 
WEAKEN AS IT TRAVERSES SHARK BAY DUE TO ENHANCED SHEAR, DRY AIR 
ENTRAINMENT, AND TERRAIN INTERACTION. UPON LANDFALL, THE SYSTEM WILL 
UNDERGO RAPID CYCLOLYSIS DUE TO INCREASED FRICTIONAL DRAG AND 
THERMODYNAMIC DECOUPLING OF THE VORTEX.

MODEL DISCUSSION: NUMERICAL WEATHER PREDICTION (NWP) CONSENSUS 
EXHIBITS HIGH CORRELATION THROUGH THE SHORT FORECAST PERIOD, 
DEPICTING MINIMAL CROSS- OR ALONG-TRACK SPREAD. THE JTWC FORECAST IS 
ALIGNED WITH THE MULTI-MODEL MEAN WITH HIGH CONFIDENCE. INTENSITY 
GUIDANCE IS ALSO CONGRUENT, WITH ALL DYNAMICAL MEMBERS DEPICTING 
RAPID WEAKENING CONCLUDING IN DISSIPATION WITHIN 24 HOURS, LENDING 
HIGH CONFIDENCE TO THE JTWC FORECAST.

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