WDXS31 PGTW 061500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (TWENTY) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.5S 119.8E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 128 NM NORTH-NORTHEAST OF PORT HEDLAND, AUSTRALIA MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 21 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL CYCLONE (TC) 20S WITH BURSTING CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC). ALONG THE SOUTHERN PERIPHERY OF THE SYSTEM, LOW-LEVEL CURVED CLOUD LINES HAVE BEEN OBSERVED QUICKLY WRAPPING BENEATH SUPPORTIVE CONVECTIVE STRUCTURES IN CLOSE PROXIMITY TO THE LLCC. ALOFT, STRONG UPPER-LEVEL OUTFLOW HAS CONTINUED WITH POLEWARD AND EQUATORWARD CHANNELS, INDICATED BY VISIBLE CIRRIFORM STRIATIONS ON ANIMATED ENHANCED WATER VAPOR IMAGERY. THE ENVIRONMENT HAS REMAINED LARGELY FAVORABLE SINCE THE PREVIOUS WARNING SIX HOURS AGO, WITH WARM SEA SURFACE TEMPERATURES OF 29-30 C, MINIMAL VERTICAL WIND SHEAR (VWS) OF LESS THAN 5 KTS, AND ROBUST OUTFLOW ALOFT. THE INITIAL POSITION HAS BEEN PLACED WITH MEDIUM CONFIDENCE BASED ON ANIMATED EIR IMAGERY AND ANIMATED COMPOSITE RADAR CENTERED IN BROOME. THE INITIAL INTENSITY HAS BEEN ASSESSED WITH MEDIUM CONFIDENCE BASED ON OBJECTIVE CIMSS INTENSITY ESTIMATES AND SUBJECTIVE AGENCY DVORAK INTENSITY ESTIMATES LISTED BELOW. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: THE NORTHWESTERN EXTENT OF A SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST, OVER EASTERN AUSTRALIA AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS CIMSS ADT: 45 KTS AT 061130Z CIMSS AIDT: 38 KTS AT 061130Z CIMSS D-MINT: 34 KTS AT 061029Z CIMSS D-PRINT: 42 KTS AT 061200Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 0-5 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THE FORECASTED TRACK REMAINS OVER WATER FOR AN ADDITIONAL 12 HOURS, ALLOWING FOR INTENSIFICATION TO 80 KTS BY TAU 36. FORECAST DISCUSSION: TC 20S IS FORECASTED TO CONTINUE SOUTHWESTWARD OVER THE NEXT 48 HOURS, ALONG THE WESTERN EXTENT OF A DEEP-LAYER STR CENTERED TO THE EAST OVER AUSTRALIAS QUEENSLAND TERRITORY. BETWEEN TAU 48 AND TAU 72, AN EXTENSION OF THE STR IN SOUTHERN WESTERN AUSTRALIA IS FORECASTED TO BEGIN RETREATING EASTWARD, ALLOWING THE TRACK FOR TC 20S TO BECOME SOUTHWARD INTO TAU 72. IMMEDIATELY FOLLOWING TAU 48, TC 20S IS EXPECTED TO MAKE LANDFALL APPROXIMATELY 20 NM SOUTH-SOUTHEAST OF LEARMONTH, AUSTRALIA, ALONG THE SOUTHERN COAST OF EXMOUTH GULF. BETWEEN TAU 48 AND TAU 72, THE CYCLONE IS FORECASTED TO CONTINUE SOUTH-SOUTHEASTWARD OVER LAND INTO SOUTHWEST WESTERN AUSTRALIA. REGARDING INTENSITY, TC 20S IS FORECASTED TO GRADUALLY INTENSIFY TO 55 KTS OVER THE NEXT 12 HOURS THROUGH THE GENERALLY SUPPORTIVE ENVIRONMENTAL ELEMENTS. FOLLOWING TAU 12, THE CYCLONE IS FORECASTED TO CONTINUE QUICKLY INTENSIFYING TOWARD 80 KTS BY TAU 36 WITH MINIMAL VWS OF LESS THAN 15 KTS, WARM SEA SURFACE TEMPERATURES BETWEEN 28-29 C, AND SUPPORTIVE POLEWARD OUTFLOW. FOLLOWING TAU 36, SEA SURFACE TEMPERATURES BEGIN DECREASING TO 26-27 C AS THE EASTERN SEMICIRCLE OF THE CYCLONES WIND FIELD EXPERIENCES TOPOGRAPHICAL FRICTION AGAINST AUSTRALIAS WEST COAST, WEAKENING SURFACE INTENSITIES TO 70 KTS BY TAU 48. ADDITIONALLY, DRY AIR BEGINS WRAPPING AROUND THE CYCLONES NORTHERN SEMICIRCLE INTO LANDFALL NEAR TAU 48, RESTRICTING FURTHER INTENSIFICATION BY LANDFALL. FOLLOWING LANDFALL IN EXMOUTH GULF, THE TERMINAL DECAY PHASE IS EXPECTED DUE TO PERSISTENT INTERACTION WITH WESTERN AUSTRALIAS RUGGED TERRAIN IN TAU 72. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE AND ARTIFICIAL INTELLIGENCE (AI) SOLUTIONS REMAIN IN TIGHT AGREEMENT INTO LANDFALL BY TAU 48, WITH A CROSS-TRACK SPREAD OF JUST 55 NM. FOLLOWING TAU 48, THE CROSS-TRACK SPREAD BEGINS TO WIDEN DUE TO UNCERTAINTIES WITH DISSIPATION OVER LAND, HOWEVER, ALL JTWC TRACK CONSENSUS SOLUTIONS ILLUSTRATE THE EXPECTED ROUNDING OF THE STR AXIS BY TAU 72 WITH A CROSS-TRACK SPREAD OF 99 NM INTO THE TERMINAL WEAKENING PHASE. THEREFORE, THE JTWC TRACK FORECAST HAS BEEN PLACED WITH HIGH CONFIDENCE AND ALIGNED NEAR THE MULTI-MODEL CONSENSUS. REGARDING INTENSITY, ALL JTWC INTENSITY CONSENSUS MEMBERS CHARACTERIZE AN INTENSIFICATION PHASE OVER THE NEXT 36 HOURS, WITH COAMPS-TC MAINTAINING LOWER INTENSITIES AT 55 KTS AND THE DETERMINISTIC GFS SOLUTION INCREASING TO 80 KTS BY THE SAME TIMEFRAME. FOLLOWING TAU 36, ALL CONSENSUS SOLUTIONS LEVEL OUT AND REMAIN STEADY UNTIL TAU 48. FOLLOWING TAU 48, ALL JTWC INTENSITY CONSENSUS MEMBERS BEGIN ILLUSTRATING A WEAKENING PHASE IN VARYING DEGREES DUE TO TOPOGRAPHICAL INTERACTION. THE JTWC INTENSITY FORECAST HAS BEEN ASSESSED WITH MEDIUM CONFIDENCE THROUGHOUT THE FORECAST PERIOD DUE TO THE QUICK INTENSIFICATION PHASE INTO TAU 36 AND THE EXPECTED WEAKENING PHASE AFTER LANDFALL AT TAU 48. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH INTENSITY 00-72 HR: MEDIUM// NNNN