Large parts of eastern Australia were put on alert for severe thunderstorms on Sunday afternoon with more potential storms and flood risk in store for Monday.

The Bureau of Meteorology said a broad line of storms had already swept through western New South Wales, while eight flood warnings were in place across southern Queensland after days of torrential rain.

Severe thunderstorms that could bring hail, damaging winds, flash flooding and power outages were likely over a huge area on Sunday afternoon, the bureau said, including across southern Queensland, western NSW, the ACT and eastern Victoria.

Wind gusts of up to 100km/h were recorded in the central west of NSW around midday on Sunday with the bureau warning residents of further likely thunderstorm warnings to come on Sunday evening.

“This is a multi-state system of storms and it’s unusually large,” said bureau meteorologist David Crock.

Crock said an area of high pressure had been sitting over the Tasman Sea for the past 10 days that had been blocking weather fronts and bringing storms and rains to southern Queensland.

“Eventually you get a strong enough system that pushes that blocking pattern away and that typically brings severe weather with it,” he said.

A front of cooler air was moving from the west on Sunday afternoon, dragging in tropical moisture from the north and bringing storm conditions to central parts of NSW and to Canberra on Sunday afternoon.

“We have a big line of storms that’s extending all the way from the Snowy mountains to the Queensland border. Behind that we are watching to see if there’s going to another band developing behind it.”

Storm activity was likely to continue through Sunday evening and into Monday in northern NSW and southern Queensland as the cold front continued to push.

“[Monday] is the last big bang of this system and that’s going to be a great relief for those people in south-east Queensland,” he said.

Southern parts of Queensland had been through a weather “whiplash” in the past week, Crock said.

Some eight flood warnings were in place over southern Queensland. The Mary River downstream of Gympie was forecast to reach major flood levels in Tiaro on Sunday evening and into Monday.

After a very dry September, southern parts of the state had seen October rainfall “multiple times their average” for the month, Crock said, with areas around the Sunshine Coast seeing between 200mm and 400mm of rain in the past week.

The bureau’s current long-range forecast for November to January suggests rainfall is likely to be above average over most of the country except the far north and much of Tasmania.

November is likely to be warmer than usual for the southern half of the continent, with night-time temperatures in particular forecast to be likely well above average over most of the country.

Global heating has seen Australia warm by about 1.5C since 1910, the bureau’s long-term climate data shows.