Parts of NSW could see more than a month’s worth of rain over three days when they are smashed by heavy storms and flooding from Wednesday, soaking the state ahead of another damp summer.

Bureau of Meteorology forecaster Jonathan How said conditions would “deteriorate” as a tropical air mass moved over the eastern states from Wednesday, when storms are expected to cover half of Australia.

“Rainfall totals this week could be record-breaking,” he said. “Daily amounts could top 150 millimetres, particularly with storms, and by week’s end some places could see their November average rainfall several times over.”

Widespread storms, intense rain, winds and potentially major flooding have all been forecast. The bureau has highlighted the areas of concern from this severe weather system as southern Queensland, eastern and northern NSW and eastern Victoria.

Mr How said the worst of the weather will be around the low-pressure system, moving into the country’s south-east on Thursday and triggering another burst of heavy rain and storms.

He encouraged people to continually check flood warnings in the coming days.

The bureau has also issued flash flood warnings for the Northern and Central Tablelands, the Riverina and parts of the Mid North Coast, which could see between 15-45mm of rain from Wednesday. Some isolated parts of the state could see up to 100mm of rain.

On Thursday alone, up to 60mm is forecast to fall in Coffs Harbour, up to 70mm in Grafton, between 50-80mm in Tenterfield and Guyra, up to 90mm at Glen Innes and up to 100mm in Moree.