October has been particularly damp, with Sydney receiving more than 100 millimetres of rain this week, central Queensland hit by severe flash flooding, and outback storms bringing destructive winds to Alice Springs. The Bureau of Meteorology said the focus for storms today is Queensland, where an influx of tropical moisture could trigger intense cells and further flash flooding, most likely over inland regions south of Longreach.
Over the central outback, including around Alice Springs, a drier atmosphere may produce strong downdrafts and gusty winds, while onshore winds bring further showers to the eastern seaboard, from Cape York Peninsula south through Brisbane and Sydney to the NSW South Coast. Stormy weather is expected to continue in Queensland and parts of NSW on Sunday, with the pattern repeating well into the new week.
Meteorologists said a high-pressure system that stalled in the southern Tasman Sea on Friday is responsible for the stagnant run of stormy days, a pattern more typical of autumn than spring. The high is forecast to remain anchored until at least next weekend. Because winds blow anticlockwise around a high in the Southern Hemisphere, its position is directing a humid supply of air off the Tasman and Coral seas onto the eastern seaboard.
From Tuesday, streams of tropical moisture from the north are also expected to arrive across southern states, expanding the zone of showers and thunderstorms. Modelling indicates most areas of Tasmania, Victoria, South Australia, NSW, the Northern Territory and Queensland can expect at least some rain during the next eight days, with the majority of regions seeing at least 15mm. For parts of Queensland and pockets of northern NSW, weekly totals are likely to exceed 50mm, and more than 100mm is possible in the Maranoa and Warrego districts, which would be about four times the October average.
The wet October is unfolding despite the Pacific El Niño already being one of the strongest on record, while the Indian Ocean is also entering a dry phase. The combination has previously been associated with widespread severe drought. However, Australia's winter was the wettest for an El Niño year in 35 years, and the national winter-spring mean is on track to exceed the long-term average.