WDPS31 PGTW 162100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19P (MEGAN) WARNING NR 006// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.4S 137.5E INITIAL INTENSITY: 65 KTS GEOGRAPHIC REFERENCE: 402 NM EAST-SOUTHEAST OF DARWIN, AUSTRALIA MOVEMENT PAST 6 HOURS: WESTWARD AT 01 KTS SIGNIFICANT WAVE HEIGHT: 21 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL CYCLONE (TC) 19P (MEGAN) HAS RAPIDLY INTENSIFIED OVER THE PAST 24 HOURS OVER THE WESTERN PORTION OF THE GULF OF CARPENTARIA. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN OBSCURED LOW LEVEL CIRCULATION CENTER (LLCC) HIDING UNDER AN EXPANSIVE CENTRAL DENSE OVERCAST (CDO), WITH OVERSHOOTING TOPS POPPING NEAR THE ASSESSED LLCC POSITION. A VERY TIMELY 161605Z AMSR2 PASS REVEALED A WELL-DEFINED MICROWAVE EYE FEATURE IN BOTH THE 37GHZ AND 89GHZ BANDS. ANALYSIS OF BOTH BANDS REVEALS THAT THE EYE IS NEARLY VERTICALLY STACKED AT THIS POINT, WITH ONLY A MINIMAL AMOUNT OF WESTERLY TILT WITH HEIGHT. THIS INDICATES THAT THE SYSTEM HAS AXISYMMETRIZED OVER THE PAST 12-24 HOURS. ADDITIONALLY THE COLOR ENHANCED 37GHZ IMAGE REVEALS A SOLID CYAN RING FEATURE, AN INDICATOR OF POSSIBLE RAPID INTENSIFICATION (RI) IN THE NEAR-TERM. OVER THE PAST 12 HOURS, RADAR DATA HAS SUGGESTED THE LLCC HAS BECOME NEARLY QUASI-STATIONARY OR IS EVEN DRIFTING BACK EAST-NORTHEASTWARD, THOUGH BEING ON THE EDGE OF THE RADAR COVERAGE OF BOTH THE GOVE AIRPORT AND MORNINGTON ISLAND RADARS, CONFIDENCE IN THE RADAR DATA IS RATHER LOW. BASED STRICTLY ON THE ABOVE MENTIONED MICROWAVE DATA AND ANALYSIS OF THE OVERALL TRENDS IN STORM MOTION, THE INITIAL POSITION WAS ASSESSED WITH HIGH CONFIDENCE. THE INITIAL INTENSITY WAS ASSESSED WITH MEDIUM CONFIDENCE, IN LINE WITH THE KNES AND ADRM DVORAK INTENSITY ESTIMATES, THE SATELLITE CONSENSUS AND THE DPRINT, BUT BELOW THE ADT AND AIDT ESTIMATES WHICH HAVE JUMPED SIGNIFICANTLY HIGHER OVER THE PAST COUPLE OF HOURS. ANALYSIS OF ANIMATED WATER VAPOR IMAGERY AND CIMSS TC-SCALE ATMOSPHERIC MOTION VECTORS SHOWS THAT WHILE THE DEEP LAYER SHEAR REMAINS IN THE MODERATE RANGE (15-20 KTS), THE PERSISTENT CONVECTIVE ACTIVITY HAS SUCCESSFULLY PUSHED BACK AGAINST THE SHEAR, WITH OUTFLOW FILAMENTS EXTENDING WELL TO THE EAST AS WELL AS NOW EXPANDING BOTH EQUATORWARD AND TO A LESSER EXTENT POLEWARD. SSTS ARE VERY WARM AND OHC IS HIGH, PROVIDING AMPLE ENERGY FOR FURTHER INTENSIFICATION. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF AN EXTENSION OF THE NEAR EQUATORIAL RIDGE (NER) CENTERED TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS KNES: T4.0 - 65 KTS ADRM: T4.0 - 65 KTS CIMSS SATCON: 64 KTS AT 161546Z CIMSS ADT: 74 KTS AT 161730Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 15-20 KTS SST: 30-31 CELSIUS OUTFLOW: MODERATE POLEWARD AND EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 19P HAS SLOWED SIGNIFICANTLY OVER THE PAST SIX HOURS OR SO AS THE NER TO THE NORTHEAST HAS WEAKENED SLIGHTLY, RELAXING THE STEERING GRADIENT. OVER THE NEXT 12 HOURS, THE NER IS FORECAST TO BUILD ONCE MORE, WHICH WILL STRENGTHEN THE STEERING INFLUENCE, AND PUSH TC 19P BACK ON A SOUTHWESTWARD TRACK TOWARDS THE COAST NEAR CENTRE ISLAND. TRACK SPEEDS ARE EXPECTED TO REMAIN FAIRLY SLOW, ONLY INCREASING TO ABOUT THREE KNOTS BY TAU 36. LANDFALL IS CURRENTLY EXPECTED JUST WEST OF CENTRE ISLAND AROUND TAU 40. AFTER MOVING INLAND AND WEAKENING, THE SYSTEM WILL COME UNDER THE STEERING INFLUENCE OF A BUILDING SUBTROPICAL RIDGE (STR) OVER SOUTHERN AUSTRALIA AND RACE OFF TO THE WEST THROUGH THE END OF THE FORECAST PERIOD. IN TERMS OF INTENSITY, THE SYSTEM HAS CLEARLY BEEN SUCCESSFUL IN PUSHING BACK AGAINST THE MODERATE EASTERLY SHEAR, GENERATING A MESOSCALE LOW-SHEAR ENVIRONMENT WHICH HAS ALLOWED FOR RAPID AXISYMMETRIZATION. THE LATEST MICROWAVE IMAGERY SUGGESTS THIS PROCESS HAS COMPLETED AND THE PRESENCE OF A CYAN RING INDICATES THAT RI IS LIKELY IN THE OFFING IN THE NEAR-TERM. OUTFLOW ALOFT IS NOT GREAT BUT GOOD ENOUGH, WHILE SSTS AND OHC VALUES ARE VERY SUPPORTIVE, HENCE THE FORECAST CALLS FOR THE SYSTEM TO UNDERGO RI OVER THE NEXT 24 HOURS, REACHING A PEAK OF 90 KNOTS. BY TAU 36, SHEAR IS EXPECTED TO INCREASE SHARPLY AS NORTHEASTERLY CONVERGENT FLOW ALOFT IS ANTICIPATED TO PUSH DOWN ON THE SYSTEM. HOWEVER, THE SYSTEM IS FORECAST TO MAINTAIN INTENSITY THROUGH LANDFALL AS THE SHEAR WILL NOT HAVE ENOUGH TIME TO SIGNIFICANTLY WEAKEN THE SYSTEM BEFORE IT MOVES INLAND. AFTER LANDFALL THE SYSTEM WILL RAPIDLY WEAKEN AND DISSIPATE OVER NORTH-CENTRAL AUSTRALIA NO LATER THAN TAU 72. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE DID NOT PICK UP ON THE ERRATIC MOTION SEEN OVER THE PAST 6 TO 12 HOURS AND FOR THE MOST PART, THE BULK OF THE GUIDANCE CONTINUES TO SHOW AN ACCELERATING TRACK TOWARDS THE COASTLINE. GFS IS THE FASTEST OF THE CONSENSUS MODELS, INDICATING LANDFALL BY TAU 24, CLOSELY FOLLOWED BY THE HAFS-A, HWRF AND COAMPS-TC. THE ECMWF HAS THE LLCC OVER LAND BY TAU 36 WHILE THE REMAINDER OF THE TRACK GUIDANCE DOES NOT SHOW LANDFALL UNTIL TAU 60. CROSS-TRACK SPREAD AT TAU 48 IS 150NM BETWEEN THE FAR OUTLIERS, NAVGEM AND GALWEM. DISCOUNTING THESE, THE REMAINDER OF THE GUIDANCE IS CONFINED TO A 40NM WIDE ENVELOPE. HOWEVER, THE FACT THAT THE MODELS HAVE NOT PICKED UP ON THE ERRATIC MOTION OVER THE PAST FEW HOURS SUGGESTS THAT THEY ARE TAKING THE SYSTEM TOO QUICKLY TO THE COAST. THE JTWC FORECAST LIES JUST NORTH OF THE CONSENSUS MEAN AT ROUGHLY THE SAME SPEED, BUT CONFIDENCE IS MEDIUM DUE TO THE UNCERTAINTY IN THE NEAR-TERM TRACK SPEED. IN THE EXTENDED FORECAST, CONFIDENCE REMAINS MEDIUM ONLY DUE TO THE SHORT-TERM FORECAST CONFIDENCE, AS ALL OF THE GUIDANCE INDICATES AN ACCELERATING TRACK TOWARDS THE WEST AFTER LANDFALL. INTENSITY GUIDANCE REMAINS SOMEWHAT MIXED WITH THE MESOSCALE MODELS (HWRF, HAFS-A, COAMPS-TC) ALL SHOWING LITTLE TO NO INTENSIFICATION PRIOR TO LANDFALL, WHILE THE SHIPS GUIDANCE ALONG WITH SEVERAL RI AIDS INCLUDING RIPA, RICN, FRIA, CHR4 AND RI35 ALL INDICATE STRONG INTENSIFICATION. PEAK INTENSITIES RANGE BETWEEN 65 AND 115 KNOTS. THE JTWC FORECAST ROUGHLY CONFORMS WITH THE RI25 AND SHIPS-GFS GUIDANCE WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN