WDXS31 PGTW 120300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (ILSA) WARNING NR 014// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 15.7S 119.9E INITIAL INTENSITY: 80 KTS GEOGRAPHIC REFERENCE: 187 NM NORTHWEST OF BROOME, AUSTRALIA MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 05 KTS SIGNIFICANT WAVE HEIGHT: 35 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY CONSOLIDATING SYSTEM, WITH CONVECTION ORGANIZING INTO WELL-DEFINED SPIRAL BANDS, WRAPPING INTO THE CORE OF THE SYSTEM. A SERIES OF WELL-TIMED MICROWAVE IMAGES INCLUDING A 112146Z SSMIS 91GHZ, A 112146Z TEMPEST 165GHZ AND A 112145Z COWVR 33.9GHZ IMAGES SHOWED A CLEAR MICROWAVE EYE FEATURE, WHICH IS BECOMING MORE VERTICALLY ALIGNED, THOUGH STILL HAS ABOUT 10NM OF TILT DOWNSHEAR AND WHICH PROVIDED HIGH CONFIDENCE TO THE INITIAL POSITION. ANIMATED HIGH- RESOLUTION VISIBLE IMAGERY THROUGH THE 0200Z HOUR SHOWS A CLEAR DIMPLE, WITH VORTICAL HOT TOWERS BEGINNING TO WRAP UPSHEAR, SUGGESTING THE SYSTEM MAY BE ATTEMPTING TO DEVELOP AN EYE. THE INITIAL INTENSITY IS ASSESSED AT 80 KNOTS WITH MEDIUM CONFIDENCE, HEDGED SLIGHTLY ABOVE THE T4.5 FIX FROM KNES AND A FEW KNOTS HIGHER THAN THE ADT AND AIDT. ANIMATED WATER VAPOR IMAGERY SHOWED STRONG GRAVITY WAVES EMANATING FROM THE EXPLOSIVE CONVECTION NEAR THE CORE, AND TRACKING OF CIRRUS DEBRIS TO THE EAST SHOWS THAT THE UPPER-LEVEL FLOW IS SPLITTING AND MOVING AROUND THE SYSTEM, LEADING TO A SIGNIFICANT REDUCTION IN THE MESOSCALE SHEAR ENVIRONMENT, SUPPORTING THE RECENT STRUCTURAL IMPROVEMENT. THE LATEST CIMSS ANALYSIS SHOWS A MEAN DEEP LAYER ENVIRONMENTAL SHEAR OF 10 KNOTS. THE SYSTEM HAS SLOWED SIGNIFICANTLY AS THE VORTEX WOBBLED AS IT CONSOLIDATED AND SYMMETRIZED BUT HAS GENERALLY BEEN MOVING TOWARDS THE WEST-SOUTHWEST ALONG THE WEST SIDE OF THE STEERING RIDGE TO THE EAST. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE EAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.0 - 65 KTS KNES: T4.5 - 77 KTS APRF: T4.0 - 65 KTS CIMSS ADT: 77 KTS AT 120000Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 5-10 KTS SST: 30-31 CELSIUS OUTFLOW: STRONG POLEWARD 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 18S WILL CONTINUE TRACKING TOWARDS THE SOUTHWEST FOR THE NEXT 12 HOURS BEFORE TURNING SOUTH, PASSING CLOSE ABOARD ROWLEY SHOALS, THEN SOUTHEAST AS IT ROUNDS THE RIDGE AXIS. ONCE PAST THE AXIS OF THE RIDGE THE SYSTEM WILL ACCELERATE TOWARDS THE SOUTHEAST AND IS EXPECTED TO MAKE LANDFALL ALONG EIGHTY MILE BEACH AROUND TAU 40. AFTER LANDFALL, THE SYSTEM GETS CAUGHT UP IN THE TIGHT STEERING GRADIENT AND WILL ACCELERATE AS IT TRACKS DEEP INTO CENTRAL AUSTRALIA. IN TERMS OF INTENSITY, THE TABLE HAS NOW BEEN SET FOR RAPID INTENSIFICATION (RI) WITH SHEAR NOW AT OR BELOW 10 KNOTS, SSTS 31C OR HIGHER, OHC INCREASING DOWN TRACK AND POLEWARD OUTFLOW STEADILY IMPROVING INTO THE DIVERGENT PORTION OF AN APPROACHING UPPER-LEVEL TROUGH. THE ONLY REMAINING FACTOR IS TIME; TIME FOR THE CONVECTIVE STRUCTURE TO CONTINUE TO IMPROVE AND FOR THE EYE TO OPEN UP AND CLEAR OUT. THIS IS ANTICIPATED TO OCCUR IN THE NEAR-TERM, LIKELY WITHIN THE NEXT 6 TO 12 HOURS. ONCE THAT OCCURS, THE GLOVES WILL COME OFF AND TC 18S WILL UNDERGO A PERIOD OF RI OR EXTREME RI (ERI), REACHING PEAK INTENSITY OF AT LEAST 130 KNOTS BY TAU 36. IT REMAINS POSSIBLE THAT THE ULTIMATE PEAK COULD BE SLIGHTLY HIGHER, OCCURRING JUST PRIOR TO LANDFALL AS THE SYSTEM PASSES OVER EXTREMELY HIGH OHC VALUES JUST OFF THE COAST. ONCE ASHORE, THE SYSTEM WILL SLOWLY WEAKEN AT FIRST AS IT PASSES OVER THE RELATIVELY FLAT TERRAIN INSHORE OF EIGHTY MILE BEACH. MORE RAPID WEAKENING IS ANTICIPATED AFTER TAU 48 DUE TO RAPIDLY INCREASING SHEAR AND LAND INTERACTION, WITH THE SYSTEM EXPECTED TO DISSIPATE NO LATER THAN TAU 72. MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD CROSS-TRACK AGREEMENT THROUGH TAU THE FORECAST PERIOD, WITH MINIMAL SPREAD IN THE MODEL GUIDANCE. ALONG-TRACK SPREAD INCREASES AFTER THE SYSTEM TURNS SOUTHEASTWARD AS THE MODELS STRUGGLE WITH DETERMINING THE TIMING AND STRENGTH OF THE RECURVE. ALONG-TRACK SPREAD AT LANDFALL IS NEARLY 90NM WITH THE GFS ENSEMBLE OUT AHEAD OF THE ECMWF WHICH IS MUCH SLOWER. THE JTWC FORECAST MOST CLOSELY TRACKS THE GFS TRACKER BUT AT A SLIGHTLY SLOWER PACE AFTER TAU 36. CONFIDENCE IS HIGH IN THE FORECAST THROUGH THE ENTIRE PERIOD. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, WITH ALL CONSENSUS MEMBERS INDICATING SIGNIFICANT INTENSIFICATION THROUGH LANDFALL. THE BULK OF THE RI GUIDANCE CONTINUES TO BE TRIGGERED, AND THE COAMPS-TC ENSEMBLE (CTCXEPS) RI PROBABILITIES REMAIN AT 100 PERCENT THROUGH TAU 36. ADDITIONALLY, THE AI-RI GUIDANCE INDICATES A HIGH LIKELIHOOD OF RI (30-40 KNOTS IN 24 HOURS) THROUGH THE SAME PERIOD JUST PRIOR TO LANDFALL. WITH THESE FACTORS IN MIND, THE JTWC FORECAST CONTINUES TO CALL FOR SIGNIFICANT INTENSIFICATION THROUGH LANDFALL, WITH A PEAK BETWEEN 130-140 KNOTS, WITH HIGH CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH INTENSITY 0 - 72 HR: HIGH// NNNN