Severe Tropical Cyclone Marcus became the strongest tropical cyclone in Australian waters for more than a decade this morning. Marcus has spent the last three days intensifying over open waters to the north of Western Australia, while gradually moving towards the west. After becoming a top-of-the-scale category five severe tropical cyclone on Wednesday, Marcus got even stronger on Thursday morning, reaching an intensity not observed in Australian waters since 2006. The Bureau of Meteorology estimated that 10 minute average wind speeds near the eye of Severe Tropical Cyclone Marcus were 230km/h at 8am WST today. According to historical records, this puts Marcus above the estimated peak average wind speeds of Ernie in 2016 (220km/h), Hamish in 2009 (215km/h), Ita in 2014 (215km/h), Marcia in 2015 (205km/h), Yasi in 2011 (205km/h) and Debbie in 2017 (195km/h). Marcus is now the strongest tropical cyclone in Australian waters since Severe Tropical Cyclone Monica in 2006, based on average wind speed. Monica's maximum average wind speed was estimated to be 250km/h, which is still the highest on record for a tropical cyclone in Australian waters. The strongest tropical cyclone on record in the southern hemisphere based on wind was Severe Tropical Cyclone Winston, which produced 10 minute average speeds of 280km/h in the South Pacific during February 2016. Severe Tropical Cyclone Marcus is expected to start weakening from today as it turns towards the south, causing it to move over cooler waters and into a less supportive environment.