The Gold Coast could be shrouded in cloudy skies as the mercury falls below a forecast low.
Key points: The mercury is forecast to drop below 20C for the rest of the day and into the early hours of Wednesday, with more rain expected to fall on ThursdayWhat is the mercury, and how do you measure it?
The mercury is measured using a barometric gauge called the Mercator Barometer.
Its readings are published every two hours.
The barometric reading is based on atmospheric pressure.
In the past, it was widely believed that the mercury was at its lowest level on January 8, the last day of the Coolidge administration, when temperatures dipped to about 14C.
In reality, it is not at its highest level for much of the year.
There are also numerous weather forecasts that suggest a range of conditions may occur on Wednesday.
The temperature forecast has the mercury at a peak around 17C and the rain is forecast at about 40mm across the region.
There is also rain forecast for parts of the Gold-Coast and parts of South Australia.
The mercury can reach between 19.8C and 21.8F in parts of Queensland.
However, a low pressure system is forecast across the country from the North East.
The rain is expected to increase to 10mm in the Hunter Valley and the Central Coast.
The mercury will reach 19C and fall below 20.9C in the Northern Territory, as well as in the South West, the South East and the South and Central Western States.
Forecasters are expecting rainfall to peak in the Adelaide CBD and in the Goldfields.
The peak in rain is estimated at 25mm across Adelaide, with the remaining areas in the CBD and Goldfields expected to see 25mm of rain.
Forecasters in Victoria are forecasting heavy rain, with temperatures expected to reach the 30C mark.
In Queensland, heavy rain is predicted, with some areas in Brisbane and the Gold Fields.
Heavy rain is also forecast for most of the state, with heavy showers expected in most parts of Southern Australia.
The forecast rainfall is expected across the Gold and Northern Rivers states, with parts of New South Wales expected to get more rain.
The heatwave that has hit parts of southern Australia is also expected to hit the Sunshine Coast and Queensland, with areas including Bundaberg and Campbelltown forecast to be in the hottest zones.
A high pressure system will move across the Australian mainland, with low pressure systems moving over parts of Western Australia, South Australia and the Northern Territories.
The heavy rain will hit parts on Wednesday, but it is expected that it will be a long and dry day.
“It is a fairly dry day, but we are seeing a lot of rain in places,” Environment Minister Greg Hunt said.
“In some parts of Bundabog you might see 20cm of rain over a couple of hours.”
We’ve got lots of rain across the state and parts.
We’re expecting the rest to come.