WDXS31 PGTW 071500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (MITCHELL) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.0S 116.7E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 201 NM NORTHEAST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 33 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 20S (MITCHELL) HAS CONTINUED A RAPID 
INTENSIFICATION (RI) TREND AS IT TRACKS SOUTHWESTWARD PARALLEL TO THE 
COAST OF AUSTRALIA NORTH OF DAMPIER. ANALYSIS OF ANIMATED ENHANCED 
INFRARED (EIR) SATELLITE IMAGERY INDICATES THAT WHILE THE SYSTEM HAS 
STEADILY INTENSIFIED OVER THE PAST SIX HOURS, IT HAS STRUGGLED TO 
MANIFEST A PERSISTENT EYE FEATURE IN THE EIR AND THE LOW-LEVEL 
CIRCULATION CENTER (LLCC) REMAINS OBSCURED BY A CONSOLIDATED CENTRAL 
DENSE OVERCAST (CDO). HOWEVER, MICROWAVE DATA, SUCH AS THE 071009Z 
WSF-M SUITE, REVEALS A WELL-DEFINED MICROWAVE EYE BENEATH THE CDO. 
THE EYEWALL STRUCTURE IS ASYMMETRIC, WITH MICROWAVE IMAGERY 
REFLECTING AN EROSION IN THE EASTERN, UPSHEAR SECTOR. ANIMATED RADAR 
DATA FROM KARRATHA STATION DEPICTS THE EYE WITH HIGH FIDELITY, 
TRANSITING NORTH OF DAMPIER AS OF 1200Z. SURFACE OBSERVATIONS FROM 
LEGENDRE ISLAND RECORDED A PEAK WIND OF 69G88KTS AT 1051Z WITH A 
MINIMUM SEA LEVEL PRESSURE (MSLP) OF 978.2MB WITHIN THE SOUTHERN 
EYEWALL. WINDS HAVE CONTINUED TO BACK AND PRESSURES ARE RISING AT 
LEGENDRE ISLAND AS THE CORE PASSES TO THE WEST. THE INITIAL POSITION 
IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE RADAR IMAGERY AND 
SURFACE OBSERVATIONAL DATA. THE INITIAL INTENSITY IS ASSESSED WITH 
MEDIUM CONFIDENCE, BASED ON A CONSENSUS OF SUBJECTIVE AND OBJECTIVE 
INTENSITY ESTIMATES. ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE; 
HOWEVER, MODERATE MID-LEVEL SHEAR HAS INCREASED BASED ON BOTH MODEL 
AND CIMSS ANALYSES, HINDERING THE DEVELOPMENT OF A PERSISTENT IR EYE 
FEATURE. OTHERWISE, STRONG POLEWARD OUTFLOW ALOFT AND ANOMALOUSLY 
WARM SSTS WITH HIGH OCEAN HEAT CONTENT (OHC) SUPPORT FURTHER MARGINAL 
INTENSIFICATION.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   DEMS: T4.0 - 65 KTS
   APRF: T4.5 - 77 KTS
   CIMSS SATCON: 81 KTS AT 070810Z
   CIMSS ADT: 79 KTS AT 071200Z
   CIMSS AIDT: 77 KTS AT 071130Z
   CIMSS D-MINT: 69 KTS AT 071009Z
   CIMSS D-PRINT: 77 KTS AT 071200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY LOWER-LEVEL AIR BEGINNING TO INTRUDE ALONG
THE NORTHERN FLANK OF THE INNER-CORE. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 20S CONTINUES TO TRACK SOUTHWESTWARD AT A
STEADY 10 KNOTS OVER THE PAST SIX HOURS, ALONG THE NORTHWESTERN
SIDE OF A LARGE STR POSITIONED OVER EASTERN AUSTRALIA. THE SYSTEM 
WILL CONTINUE THIS TRAJECTORY OVER THE NEXT 24 HOURS, BUT FORWARD 
SPEED WILL DIMINISH AS IT APPROACHES THE RIDGE AXIS. LANDFALL IS 
FORECAST ALONG THE NORTHEASTERN COAST OF THE EXMOUTH GULF, SOUTHWEST 
OF ONSLOW AROUND TAU 24. THE SYSTEM WILL THEN BEGIN A GRADUAL 
SOUTHEASTWARD RECURVATURE, MOVING DOWN THE EASTERN MARGIN OF THE 
EXMOUTH GULF. BY TAU 36, TC 20S WILL REACH THE RIDGE AXIS AND BEGIN A 
GRADUAL TURN TOWARDS THE SOUTHEAST, ACCELERATING FURTHER INLAND 
THROUGH THE REMAINDER OF THE FORECAST PERIOD. THE CURRENT TRACK CALLS 
FOR TC 20S TO SKIRT THE EASTERN COAST OF THE EXMOUTH GULF AFTER TAU 
24; HOWEVER, BASED ON A CONTINUED WESTWARD TREND IN THE GUIDANCE 
PACKAGE, THERE IS INCREASING POTENTIAL THE CENTER WILL TRAVERSE THE 
CENTER OR WESTERN SIDE OF THE GULF REMAINING OVER WATER FOR A LONGER 
PERIOD OF TIME. REGARDING INTENSITY, DESPITE MODERATE MID-LEVEL SHEAR 
AND DRY AIR ENTRAINMENT, THE SYSTEM IS EXPECTED TO MAINTAIN OR 
SLIGHTLY INCREASE INTENSITY DURING ITS SHORT REMAINING TIME OVER 
WATER. SHEAR IS FORECAST TO DECREASE SLIGHTLY WHILE AN UPPER-LEVEL 
TROUGH APPROACHING FROM THE SOUTHWEST WILL ENHANCE POLEWARD OUTFLOW. 
THE PRIMARY UNCERTAINTY IS WHETHER TC 20S CAN RESIST DISRUPTION LONG 
ENOUGH TO LEVERAGE THIS IMPROVED OUTFLOW. THE FORECAST SAYS YES; IT 
REMAINS TO BE SEEN WHAT NATURE HAS TO SAY. ONCE THE SYSTEM MAKES 
LANDFALL AND CURVES INLAND, IT WILL RAPIDLY WEAKEN DUE TO FRICTIONAL 
EFFECTS, INCREASING SHEAR AND DRY AIR ENTRAINMENT, DISSIPATING NO 
LATER THAN TAU 72. 

MODEL DISCUSSION: NUMERICAL WEATHER PREDICTION (NWP) GUIDANCE HAS 
STEADILY SHIFTED WESTWARD; CONSEQUENTLY, THE BULK OF THE CONSENSUS 
MEMBERS HAVE SHIFTED INTO THE EXMOUTH GULF. ALL MEMBERS OF THE MULTI-
MODEL PACKAGE ARE NOW CONCENTRATED WITHIN THE GULF, WITH THE 
EXCEPTION OF THE GEFS AND NAVGEM. THE JTWC FORECAST IS POSITIONED ON 
THE EASTERN PERIPHERY OF THE GUIDANCE ENVELOPE, WITH MEDIUM 
CONFIDENCE. A WESTWARD CROSS-TRACK SHIFT TOWARD LEARMONTH REMAINS A 
VIABLE ALTERNATE SCENARIO. INTENSITY GUIDANCE EXHIBITS LOWER 
CONVICTION, WITH MESOSCALE MODELS INDICATING THE SYSTEM HAS REACHED 
PEAK INTENSITY. THE ONLY AIDS INDICATING ADDITIONAL INTENSIFICATION 
ARE SHIPS (NAVGEM/GFS), WHICH PROJECT A PEAK INTENSITY NEAR 85 KNOTS 
PRIOR TO LANDFALL. THE JTWC FORECAST IS ALIGNED WITH SHIPS GUIDANCE 
WITH MEDIUM CONFIDENCE.

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