A storm outbreak will gradually replace a heatwave across southern Qld and parts of northern Australia over the coming days. Sky News Chief Meteorologist Tom Saunders explains.

The east coast is set for an absolute drenching for the next couple of days with possible severe thunderstorms and “flash flooding a real threat,” forecasters have warned.

With up to 60mm set to fall on Thursday, Sydney could see more than half its average March rain fall in a single day.

It comes as a severe heatwave centred on south east Queensland starts to weaken. Suburbs and towns close to Brisbane soared to above 40C on Tuesday, easily beating all time March records.

Ipswich, Gatton and Archerfield all exceeded their previous monthly top temperatures.

But further south, across Victoria and Tasmania, mild autumnal conditions are the order of the day.

“The heatwave for Queensland will continue but it will slowly recede and for Queensland and NSW, storms will be increasing and will be a main feature for rest of the week,” said Sky News Weather channel meteorologist Rob Sharpe.

RAIN FOR NSW AND QUEENSLAND

Brisbane temperatures currently in the low thirties will dip into the high twenties on the weekend as the rain threat increases with possible storms.

In some areas torrential rain has already arrived. Gladstone saw almost 80mm of rain fall in just one hour on Tuesday evening.

In a relief to drought stricken farmers, some of that rain could make its way into central Queensland over the coming days.

Sydney saw its best rainfall since early February on Wednesday morning with almost 20mm falling on the CBD.

There’s every likelihood that’s a mere drop in the ocean. Three times that amount could fall on Thursday. And forecasters have said even that could be an underestimate.

Showers in NSW could link up with the storms in Queensland.

“A coastal trough will trigger heavy rain and storms along the NSW coast on Thursday and Friday most likely around the Illawarra and Sydney,” Sky News Weather’s Tom Saunders told news.com.au.

According to the Bureau of Meteorology, there will be highs of around 25C on a stormy Thursday in Sydney with up to 60mm of rain then 15mm on Friday as the storms persist.

Sydney hasn’t seen that much rain since last November. The average CBD rainfall for March is 100mm.

Wollongong could see around 65mm of rain over the next few days and around 45mm could fill the gauge in Newcastle.

Wet days coming up for the coast. Tomorrow looks like it will be the wettest between the Illawarra Coast and the Central Coast (with Sydney right in the middle) ☂️. Explore the details at https://t.co/1yxAIPrpyJ ("50% chance of more than" map below). pic.twitter.com/bXtKG8VGBo — Bureau of Meteorology, New South Wales (@BOM_NSW) March 12, 2019

“The trough is supported by an unstable atmosphere due to an upper trough over southeast Australia overriding a humid, warm Tasman Sea air mass,” said Mr Saunders.

“This will further enhance rain along the surface trough and we could easily see totals well above what is indicated by models.”

Mr Saunders said flash flooding was a “real threat” along the coastal fringe from Thursday afternoon and into Friday.

Like in Queensland, some of that rain could extend further inland as the weekend nears.

As you move further south the rain totals will drastically fall. Canberra will be cloudy but might experience just a few millimetres of rain and likely no storms, although it could be wetter on the NSW south east coast.

Did you have to rug up last night? The cool change💨 ❄️ yesterday led to overnight minima well below average. Don't get too excited for the change of season just yet though - much warmer temps expected by the weekend! Forecasts: https://t.co/U0Uokv3ocF #VicWeather pic.twitter.com/jdz4kJ6hiX — Bureau of Meteorology, Victoria (@BOM_Vic) March 12, 2019

OTHER STATES AND CYCLONE THREAT

Melbourne is looking sunny with highs of 20-23C rising to almost 30C on the weekend. But the nights have been chilly dipping close to single digits in the city; in Swan Hill it fell to 5C early this morning.

Mild and sunny in Hobart rising from 17C today to 25C on the weekend.

Sunny and warm in South Australia. 23C in Adelaide on Wednesday with the mercury hitting 33C on Sunday.

Across the Nullarbor in Perth, expect summery and sunny conditions for days to come with the mercury in the low thirties.

Trouble is brewing around Darwin, however with a series of topical lows bubbling up north of Australia. These could form into cyclones in the week to come.

Around 34C and stormy in the Top End.