A grandfather has died in floodwaters south-west of Brisbane, as Queensland braces for more severe weather, with NSW also expected to cop thunderstorms and downpours.

A white ute belonging to 71-year-old Peter Wells was found wedged between trees on an embankment at Greenbank, where more than 100 millimetres of rain fell in an hour on Wednesday night.

Police called to conduct a welfare check at a private property early on Thursday found Wells’ body nearby.

Acting Commissioner Steve Gollschewski said police were investigating the death.

“Our investigation is underway as to what the circumstances were,” he said.

“Early days on that yet, but clearly an absolutely tragic circumstance.”

Gollschewski said emergency services had to rescue other people who had driven into floodwaters in the same area. He said the SES had received 12 calls for help across the region overnight.

Queensland is forecast to endure more wet weather on Thursday, with a severe weather warnings issued for the central-west, Maranoa and Warrego regions.

Sydney and much of NSW can also expect a drenching as a deepening coastal trough and associated upper-level low pressure system bring widespread rain to much of Australia’s east by Saturday.

“A thick stream of dense clouds and heavy rain will soak Sydney and other areas of eastern NSW over the next three days, with damaging winds and hazardous surf also on the cards from Friday,” forecaster Weatherzone said.

“While this weather pattern will produce severe weather that could include a month’s worth of rain in 24 hours for some places, it is not unusual for this time of year.”

The twin weather systems are likely to produce a deep coastal trough that will develop into a phenomenon called a black nor’easter – heavy, dark clouds, torrential rain and strong north-easterly winds.

“Black nor’easters typically bring a mix of severe weather and make the day appear darker beneath a blanket of thick rain-bearing clouds,” Weatherzone said.

Many areas are likely to get more than 100 millimetres of rain in coming days, while parts of Sydney, the Blue Mountains, the Hunter, Illawarra and South Coast could get 200 millimetres, or even 250 millimetres in some regions.

The Bureau of Meteorology’s Angus Hines said more warnings could be issued throughout Thursday as thunderstorms moved through southern Queensland.

“The most vigorous activity is generally over that Maranoa and Warrego region but potentially a little bit later today that could move somewhere else,” he said.

“The primary threat is going to be heavy rainfall, much like it was last night, localised pockets of very heavy rainfall.”

Major flooding is predicted along the Bremer River on Thursday, with water levels already up sharply following Wednesday night’s heavy rain.

Moderate flooding is also possible in parts of the southern inland and south-west of Queensland, including the Condamine, McIntyre, Weir, Warrego and Moonie rivers.

For residents near the Moonie and Condamine rivers, it is just a few months since river levels last rose, flooding homes in a January emergency.

The weather system will also move south into northern NSW, developing into a low-pressure system.

The state’s north-east had a wet night on Wednesday, with 70 millimetres falling at Nashua and 64.5 millimetres in two hours at Walllis Lakes. Hines said NSW could expect more heavy rain in coming days.

“As we push through today and tomorrow, the rain is actually going to turn a little bit more widespread,” he said.

“Today we do have some further thunderstorms expected in the north, which could bring some pockets of very heavy rainfall for the northern rivers and the north-west.”

The system is expected to track further south to the Hunter, Sydney, Blue Mountains and Illawarra on Friday.

-with AAP