Sydney, Brisbane weather: Mega rain event known as the ‘Black Nor’easter’ is about to strike with 300m blast – here’s when

Parts of New South Wales and Queensland, including Sydney and Brisbane, will be drenched with up to 300mm of rain as two weather systems merge and wreak havoc on the east coast.

Met offices have warned that those living in south-east Queensland to the south coast of New South Wales will have a miserable few days from Thursday to Saturday.

Heavy rain is expected to fall over the next 72 hours, with 300mm forecast along the east coast and 200mm possible in isolated areas.

Sydney could be inundated with up to 100mm of rain on Friday alone.

The wild weather will also bring something known as Black Nor’easter, which is when a violent storm bringing black clouds sends areas into darkness even in the middle of the day.

The most severe weather will be seen on Friday, with widespread falls of 50mm to 100mm of rain falling from Brisbane to the New South Wales south coast.

In the coming days, Sydney, the Blue Mountains and the Illawarra region could receive between 200 and 300mm of rain, Weatherzone’s Joel Pippard said.

“Some models show rainfall of up to 80-150 mm in just six hours, and strong storms are possible in these regions,” he said.

“Similar heavy falls are also possible on the northern tablelands of New South Wales, the northwest slopes and plains and the Darling Downs and Granite Belt of Queensland during Thursday and Friday mornings.”

Thunderstorms are also possible over northeastern New South Wales and southeastern Queensland on Thursday afternoon.

Strong seas and winds with gusts of up to 100 kilometers per hour are also forecast.

The reason for the wild weather is the combination of an upper-level low pressure system and a coastal trough forming off the east coast.

This coastal trough will funnel tropical moisture from the north, causing heavy rain.

Miriam Bradbury of the Bureau of Meteorology warned that the heaviest rain and strongest winds will be recorded on Friday.

“As we move through the latter part of Thursday into Friday, that’s when we’ll see the more severe weather begin to intensify as a trough deepens off the east coast of New South Wales,” he said.

“Precipitation of this magnitude can cause flash flooding.”

The wild weather is expected to improve on Saturday as the system moves further south.

Sydney could receive up to 40mm of rain on Thursday, while the forecast for Friday says between 25mm and 100mm is possible.

Up to 50mm is forecast for Saturday, while the sun will finally come out on Sunday for a warm 28C day.

Wollongong, south of Sydney, could receive up to 130mm of rain on Friday and 80mm on Saturday.

Further south in Batemans Bay there will also be rain, with up to 100mm on the horizon for Saturday.

Katoomba, in the Blue Mountains, could be hit by up to 150mm on Saturday.

Brisbane is also in the firing line, with the potential for 70mm of rain over the next three days.

Canberra will also be hit by rain with forecasts of up to 40mm on Friday and a maximum of 45mm on Saturday.

Melbourne will miss out on miserable weather with dry and partly cloudy days forecast for the end of the week.

Those in Adelaide will enjoy a dry and sunny weekend, as will those in Perth, with temperatures around 30 degrees.

Darwin will see some possible showers over the next few days.