TC 19P(MEGAN) to peak within 12/24H at CAT 2 US crossing the Pellew Group within 24H//TC 18S struggling//

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 19P AND ON TC 18S

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL CYCLONE 19P (MEGAN) HAS CONTINUED TO RAPIDLY INTENSIFY OVER THE ZESTY WATERS OF THE SOUTHERN GULF OF CARPENTARIA. AFTER ACHIEVING A VERTICALLY ALIGNED VORTEX THIS MORNING, THE SYSTEM HAS CONTINUED TO DEVELOP A STRONGER INNER-CORE OF DEEP CONVECTION, THOUGH AS OF YET HAS NOT FORMED AN EYE FEATURE IN EITHER THE VISIBLE OR INFRARED CHANNELS. THE LATEST ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS VERY DENSE INNER-CORE CONVECTIVE ACTIVITY, WITH OVERSHOOTING TOPS AND CLOUD TOP TEMPERATURES AS LOW AS -94C. ADDITIONALLY, AN EXTREMILY POTENT INNER-CORE LIGHTNING BURST IS ONGOING, WHICH IS A STRONG INDICATOR OF ADDITIONAL INTENSIFICATION IN THE OFFING. A 161958Z SSMIS 91GHZ MICROWAVE IMAGE REVEALED A WELL-DEFINED MICROWAVE EYE, THOUGH THE EYE IN THE 37GHZ BAND HAD A MUCH WEAKER REPRESENTATION. REGARDLESS, TRACKING OF THE EYE FEATURE SHOWED THAT THE SYSTEM MADE A SMALL CLOCKWISE LOOP BETWEEN 1200Z AND 2000Z AND IS NOW TRACKING TOWARDS THE SOUTHEAST. THE INITIAL POSITION WAS ASSESSED WITH MEDIUM CONFIDENCE, UNDER THE COLDEST CLOUD TOPS IN THE EIR WITH SUPPORT FROM RADAR POSITIONING DATA. THE INITIAL INTENSITY WAS ASSESSED WITH MEDIUM CONFIDENCE, ON THE HIGHER END OF THE AVAILABLE OBJECTIVE AND SUBJECTIVE FIXES NOTED BELOW. THE ENVIRONMENT REMAINS FAVORABLE, WITH LOW TO MODERATE EASTERLY ENVIRONMENTAL SHEAR, VERY WARM SSTS, HIGH OHC AND MODERATE WESTWARD AND EQUATORWARD OUTFLOW.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 19P HAS COMPLETED A TIGHT CLOCKWISE LOOP OVER THE PAST SIX HOURS, HAVE ABSCONDED BRIEFLY IN A WEAK STEERING ENVIRONMENT. BUT NOW IT HAS PICKED UP SOME SPEED, HEADED TOWARDS THE SOUTHWEST COAST OF THE GULF OF CARPENTARIA, ALONG THE WESTERN SIDE OF A MID-LEVEL NER CENTERED TO THE NORTHEAST. THE NER IS EXPECTED TO WEAKEN SOMEWHAT OVER THE NEXT 12 TO 24 HOURS, WHICH WILL LOOSEN THE STEERING GRADIENT BY A NOTCH OR TWO, THUS ALLOWING TC 19P TO SLOW DOWN TO 2-3 KNOTS AS IT APPROACHES THE COAST. LANDFALL IS EXPECTED AROUND TAU 24 IN THE VICINITY OF THE SIR EDWARD PELLEW GROUP. AFTER LANDFALL, TRACK SPEEDS WILL REMAIN LOW OR EVEN SLOW A BIT MORE AS A WEAKNESS DEVELOPS IN THE MID-LEVEL RIDGE PATTERN. AFTER TAU 48 THE SYSTEM WILL BEGIN TO ACCELERATE WESTWARD AS IT COMES UNDER THE INFLUENCE OF A BUILDING SUBTROPICAL RIDGE (STR) TO THE SOUTH. IN TERMS OF INTENSITY, THE SYSTEM HAS CONTINUED TO RAPIDLY INTENSIFY, EVEN IN THE FACE OF MODERATE EASTERLY ENVIRONMENTAL SHEAR. NO SIGNIFICANT CHANGES ARE EXPECTED IN THE OVERALL ENVIRONMENT OVER THE NEXT 12 TO 18 HOURS, THUS THE SYSTEM IS FORECAST TO CONTINUE TO INTENSIFY, UP TO A PEAK OF 95 KNOTS BY TAU 12. THE SYSTEM WILL MAINTAIN THIS PEAK INTENSITY THROUGH LANDFALL EVEN AFTER DEEP-LAYER ENVIRONMENTAL SHEAR ALONG WITH A BURST OF CONVERGENT NORTHEASTERLY FLOW ALOFT, MOVES IN AROUND TAU 18. ONCE ASHORE HOWEVER, THE SYSTEM WILL QUICKLY WEAKEN AND ULTIMATELY DISSIPATE OVER NORTH-CENTRAL AUSTRALIA BY TAU 72.

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT AND HAS IMPROVED SINCE THE PREVIOUS RUN, WITH NO SIGNIFICANT OUTLIERS AT THIS TIME. THE TRACK SPREAD HAS REDUCED TO JUST 100NM BY THE END OF THE FORECAST PERIOD. HOWEVER, TRACK SPEED IS THE MORE DOMINANT CONCERN AND THERE IS A SIGNIFICANT AMOUNT OF ALONG-TRACK SPREAD, PARTICULARLY IN THE FIRST 36 HOURS OF THE FORECAST. THE JTWC FORECAST TRACKS CLOSE TO THE CONSENSUS MEAN IN BOTH DIRECTION AND SPEED, BUT CONFIDENCE IS ONLY MEDIUM DUE TO THE POSSIBILITY OF A FASTER SPEED OF ADVANCE IN THE FIRST 36 HOURS OF THE FORECAST. INTENSITY GUIDANCE REMAINS MIXED, WITH THE MESOSCALE MODELS (HWRF, HAFS-A, AND COAMPS-TC) STUBBORNLY REFUSING TO ACKNOWLEDGE THE POSSIBILITY OF ADDITIONAL INTENSIFICATION, AS THEY HAVE BEEN DOING SINCE YESTERDAY. THE MESOSCALE MOELS ALL SHOW THE SYSTEM MAINTAINING INTENSITY TO TAU 12 THEN FALLING OFF SHARPLY THEREAFTER. MEANWHILE, THE SHIPS GUIDANCE (BOTH GFS AND NAVGEM) SHOW AN ADDITIONAL 15-20 KNOTS OF INTENSIFICATION, PEAKING AT 100 KTS, WHILE THE FRIA, RICN, RIPA AND RI25 TO RI 35 RAPID INTENSIFICATION AIDS CONTINUE TO TRIGGER, PEAKING THE SYSTEM NEAR 125 KNOTS BY TAU 24. IF THE SYSTEM HAD MORE TIME OVER WATER, THE RI PEAKS MIGHT BE REALISTIC, BUT WITH REALISTICALLY NO MORE THAN 12 HOURS OF OPEN WATERS, THE JTWC FORECAST PEAKS AT 95 KNOTS.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS LOW-LEVEL CLOUD BANDS WRAPPING INTO TROPICAL CYCLONE 18S, THOUGH THE LOW LEVEL CIRCULATION CENTER (LLCC) REMAINS OBSCURED BY PLUMES OF FLARING CONVECTION. AS EASTERLY VERTICAL WIND SHEAR (VWS) HAS DECREASED OVER THE LAST SIX HOURS TO 15-20KTS, THE VERTICAL STRUCTURE OF THE SYSTEM HAS IMPROVED SLIGHTLY. THE SYSTEM REMAINS QUASI-STATIONARY (QS) IN THE REGION, CONTINUING OCEANIC UPWELLING AND DRAINING THE OCEAN HEAT CONTENT. THE SYSTEM HAS DRIFTED TO THE SOUTHEAST WHILE REMAINING IN A COMPETING STEERING ENVIRONMENT ON THE SOUTHERN PERIPHERY OF A NEAR EQUATORIAL RIDGE (NER) TO THE NORTH AND A SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. OUTFLOW WAFTS WEAKLY POLEWARD AS WINDS ARE NOT VERY DIVERGENT ALOFT. THE INITIAL POSITION WAS ASSESSED WITH LOW CONFIDENCE BASED ON ANIMATED MSI DEPICTING WELL-DEFINED CLOUD BANDS WRAPPING FROM THE NORTHWEST INTO A CENTER BENEATH THE CONVECTION. THE INTENSITY WAS ASSESSED WITH LOW CONFIDENCE BASED ON AGENCY AND OBJECTIVE FIXES LISTED BELOW.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 18S IS FORECAST TO REMAIN IN A QS STATE FOR THE NEXT 48 HOURS BEFORE BEING DRIVEN WESTWARD BY A BUILDING NER TO THE SOUTHEAST OVER CONTINENTIAL AUSTRALIA. AS THE SYSTEM PICKS UP TRACK SPEED BY TAU 72, THE SYSTEM IS EXPECTED TO REACH 8KTS BY THE END OF THE FORECAST PERIOD. TC 18S IS FORECAST TO STRUGGLE TO INTENSIFY IN THE NEAR-TERM AND REMAIN ALMOST STAGNANT FOR THE FIRST 24 HOURS. AS THE SYSTEM MOVES AWAY FROM THE REGION BETWEEN TAU 48-72, VWS SHOULD REMAIN FAVORABLE ALLOWING FOR SLOW INTENSIFICATION DESPITE CONTINUING INTO A REGION OF RELATIVELY COOLER WATERS AND LOWER OCEAN HEAT CONTENT. BY THE END OF THE FORECAST PERIOD, THE SYSTEM IS EXPECTED TO INCREASE TO A PEAK OF 45KTS AS THE ENVIRONMENT IMPROVES.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GENERALLY GOOD AGREEMENT THAT THE SYSTEM WILL REMAIN QUASI-STATIONARY BEFORE TRACKING TO THE WEST BETWEEN THE 48-72 HOUR POINT. THE MAXIMUM CROSS TRACK SPREAD BY THE END OF THE FORECAST OPENS TO 400NM BY THE END OF THE FORECAST PERIOD, WITH ECM2 TO THE NORTH AND NAVGEM TO THE SOUTH. THE INTENSITY GUIDANCE HAS CHANGED DRASTICALLY OVER THE LAST SIX HOURS, WITH HAFS-A DROPPING FROM A PEAK OF 150KTS ON THE 161200Z RUN TO A PEAK OF 40KTS IN THE CURRENT RUN. JTWC SHIPS GUIDANCE AND HWRF BOTH REMAIN HIGH, PEAKING AT 85KTS BY TAU 120. THE SIGNIFICANT DEVIATION BETWEEN MODEL RUNS HAS CAUSED GREAT UNCERTAINTY AND LOW CONFIDENCE IN THE INTENSITY FORECAST.