WDXS31 PGTW 062100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (MITCHELL) WARNING NR 004// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.9S 119.0E INITIAL INTENSITY: 50 KTS GEOGRAPHIC REFERENCE: 87 NM NORTH-NORTHEAST OF PORT HEDLAND, AUSTRALIA MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 18 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL CYCLONE 20S (MITCHELL) WITH IMPROVING CURVED DEEP CONVECTION WRAPPING INTO THE CENTER. A 061720Z AMSR2 36 GHZ MICROWAVE IMAGE REVEALED THAT THE SYSTEM NOW HAS A DEFINED MICROWAVE EYE FEATURE. THE 89 GHZ VERSION OF THE SAME PASS SHOWS TIGHTLY CURVED CONVECTIVE BANDING SURROUNDING THE ASSESSED CENTER FROM ALL SIDES, INDICATING A DEVELOPING STORM. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED LARGELY ON ANIMATED EIR IMAGERY DUE TO THE LATE RECEIPT OF THE AMSR2 IMAGE. A SMALL ADJUSTMENT TO THE INITIAL POSITION BASED ON THE AMSR2 IMAGE WOULD RESULT IN THE CENTER BEING SHIFTED ABOUT 15 NM TO THE NORTHEAST. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 20S IS IN A HIGHLY FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE CENTERED FAR TO THE EAST-SOUTHEAST, OVER EASTERN AUSTRALIA AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS APRF: T3.0 - 45 KTS CIMSS ADT: 51 KTS AT 061800Z CIMSS AIDT: 39 KTS AT 061800Z CIMSS D-MINT: 46 KTS AT 061720Z CIMSS D-PRINT: 45 KTS AT 061800Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 5-10 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: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 20S IS FORECAST TO TRACK SOUTHWESTWARD, ALONG THE NORTHWESTERN PERIPHERY OF THE STR, THROUGH TAU 36. LANDFALL IS FORECAST TO OCCUR NEAR THE EXMOUTH GULF AROUND TAU 36. THE PRECISE LANDFALL LOCATION COULD VARY IN RESPONSE TO SMALL CHANGES TO THE TRAJECTORY, POTENTIALLY ALLOWING FOR A DIRECT LANDFALL TO THE NORTH WEST CAPE. AS IT STANDS, LANDFALL IS FORECAST TO OCCUR JUST EAST OF THE EXMOUTH GULF. AFTER TAU 36, THE STR IS EXPECTED TO PROPAGATE WESTWARD, ANCHORING OVER CENTRAL AUSTRALIA. THIS WILL CAUSE 20S TO BEGIN TURNING SOUTHWARD AND THEN SOUTHEASTWARD AS IT ROUNDS THE WESTERN EXTENT OF THE STR. REGARDING INTENSITY, 20S IS FORECAST TO RAPIDLY INTENSIFY OVER THE NEXT 24 HOURS TO A PEAK OF 80 KTS IN RESPONSE TO THE HIGHLY FAVORABLE ENVIRONMENT. ONCE THE SYSTEM BEGINS TO INTERACT MORE WITH THE COAST OF AUSTRALIA, 20S WILL BEGIN A WEAKENING TREND. AFTER TAU 48, A MORE RAPID WEAKENING TREND WILL ENSUE DUE TO INCREASING SHEAR AND DRY AIR ENTRAINMENT FROM THE WEST. WEAKENING BELOW TC STRENGTH IS FORECAST TO OCCUR NEAR TAU 72 AS THE SYSTEM TRACKS FURTHER INLAND, EAST OF SHARK BAY. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN VERY GOOD AGREEMENT WITH THE EXCEPTION OF NAVGEM, WHICH TRACKS THE SYSTEM MUCH FURTHER WEST THAN THE REMAINDER OF GUIDANCE. DISCOUNTING NAVGEM, THERE IS A MERE 20 NM CROSS-TRACK SPREAD AT TAU 36. CROSS-TRACK SPREAD THEN INCREASES SLIGHTLY TO 65 NM AT TAU 72. THE TIGHT AGREEMENT BETWEEN MODELS LENDS HIGH CONFIDENCE TO THE JTWC TRACK FORECAST. INTENSITY GUIDANCE IS IN MODERATE AGREEMENT WITH MODELS SHOWING INTENSIFICATION THROUGH TAU 12-24. PEAK INTENSITIES RANGE FROM 65 KTS (COAMPS-TC) TO 80 KTS (HWRF). THE JTWC INTENSITY FORECAST IS PLACED CLOSER TO HWRF AND HAFS-A DUE TO THE EXPECTED HIGHLY FAVORABLE ENVIRONMENT THROUGH LANDFALL. MODELS THEN AGREE ON WEAKENING FROM TAU 36 ONWARD. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH INTENSITY 00-72 HR: MEDIUM// NNNN