WDXS31 PGTW 070300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 20S (MITCHELL) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.0S 118.4E INITIAL INTENSITY: 60 KTS GEOGRAPHIC REFERENCE: 79 NM NORTH OF PORT HEDLAND, AUSTRALIA MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 18 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL CYCLONE 20S (MITCHELL) WITH TIGHTLY CURVED DEEP CONVECTION WRAPPING INTO THE CENTER. THE MSI ALSO HAS SHOWN HINTS OF AN EYE FORMING OVER THE LAST FEW HOURS WITH A SLIGHT WARM SPOT DEVELOPING. A 062137Z WSFM 37 GHZ MICROWAVE IMAGE REVEALED THAT THE MICROWAVE EYE HAS BECOME MORE DEFINED AND SYMMETRICAL. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON ANIMATED RADAR IMAGERY FROM PORT HEDLAND ALONG WITH THE MSI. THE INITIAL INTENSITY OF 60 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE HIGH END OF THE AGENCY DVORAK FIXES AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 20S REMAINS 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: T3.5 - 55 KTS APRF: T3.5 - 55 KTS CIMSS ADT: 51 KTS AT 070010Z CIMSS AIDT: 42 KTS AT 070010Z CIMSS D-MINT: 54 KTS AT 062139Z CIMSS D-PRINT: 60 KTS AT 070010Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD AND EQUATORWARD 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 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 CONTINUE INTENSIFYING OVER THE NEXT 12- 24 HOURS TO A PEAK OF AROUND 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. NEAR TAU 48, 20S WILL ENCOUNTER INCREASING VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT, FURTHER AIDING IN WEAKENING THE VORTEX. 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 25 NM CROSS-TRACK SPREAD AT TAU 36. CROSS-TRACK SPREAD THEN INCREASES TO 75 NM AT TAU 72. THE CLOSE 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. NOTABLY, MULTIPLE RAPID INTENSIFICATION (RI) AIDS HAVE TRIGGERED THIS RUN. ON THE OTHER END, HAFS-A APPEARS TO BE INCORRECTLY PORTRAYING THE SYSTEM THIS RUN, SHOWING NO INTENSIFICATION AT ALL. THE JTWC INTENSITY FORECAST IS PLACED CLOSER TO HWRF, CALLING FOR A PEAK OF 80 KTS, WITH MEDIUM CONFIDENCE. THERE IS A POSSIBILITY THAT AN EVEN HIGHER PEAK OCCURS BEFORE LANDFALL DUE TO THE HIGHLY FAVORABLE ENVIRONMENT, AS INDICATED BY THE RI AIDS. MODELS THEN AGREE ON WEAKENING FROM TAU 36 ONWARD. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH INTENSITY 00-72 HR: MEDIUM// NNNN