After the recent heatwave in the eastern states and flooding in the north, afternoon showers and thunderstorms are likely across Queensland, including Brisbane.

In NSW, there will be onshore winds and cloudy skies, with some showers likely in Sydney and elsewhere.

In Victoria and Tasmania, southeasterly winds are forecast to bring cloud and cooler-than-average temperatures, with morning showers ahead of clearing conditions in the afternoon for Melbourne and Hobart.

Adelaide can expect some sunshine, after a cool and cloudy start for Christmas morning over South Australia.

In Western Australia, a low-pressure system has been brewing this week and could bring showers and storms to the interior as well as Perth, interspersed with sunshine.

The Northern Territory can expect seasonal afternoon showers and storms around Darwin, although the risk of any Christmas impacts due to the remnants of ex-tropical cyclone Jasper appears unlikely, the Bureau of Meteorology said.

TEMPERATURE RANGES FOR CAPITAL CITIES ON THE DAY:

* Sydney: 19-28C

* Canberra: 13-23

* Melbourne: 16-23

* Brisbane: 22-33

* Hobart: 14-21

* Adelaide: 13-23

* Perth: 22-33

* Darwin: 29-34

Meanwhile, fish markets are gearing up for a final push as Australians shop for one of the most popular fares for the Christmas table - seafood.

The Sydney Fish Market, one of the biggest in Australia, is open from 5am Saturday to 5pm on Christmas Eve and expects to sell more than 350 tonnes, including 120 tonnes of prawns and about 70,000 dozen oysters.

More than 100,000 people are expected to visit the market in the inner city suburb of Pyrmont in the next 36 hours.

The most popular items are usually barramundi, snapper, lobsters, and of course prawns and oysters.

There are also "affordably delicious" fish like school whiting, gurnard, and ocean jacket.

"We encourage visitors to come with an open mind and menu, and let our expert retailers guide you towards the catch of the day," market chief executive Greg Dyer said.

Australian Associated Press