MELBOURNE (REUTERS) - Temperatures soared on Monday (Dec 30) in Australia's normally icy cool state of Tasmania, the country's closest point to the South Pole, reaching more than double the summer average with hot air blowing in from a scorching mainland.

The mercury in the state's capital Hobart hit 40.8 deg C, which would make it the city's hottest December day on record, the Bureau of Meteorology said.

The unusual summer temperatures, even in the country's coldest places, stem from the extreme conditions that have stoked one of Australia's worst bush fire seasons.

"The reason it's getting this hot in Tasmania is we've got quite strong northerly winds bringing that hot air down from the mainland," said meteorologist Luke Johnston.

The temperature on Monday was double the average summer level of 20 degrees for Hobart and even topped temperatures in the country's tropical north. In northern Darwin, temperatures hit a maximum of 35 deg C, while it was 39 deg C in central Alice Springs.

At midday, a sharp wind change drove Hobart's temperature up by eight degrees in just 10 minutes, with the threat of lightning prompting fire danger alerts from the state's fire service.

A cool change was forecast for Tuesday.

Tasmania's normally cooler weather attracts vintners from the mainland, where a changing climate has started to affect some acclaimed winemaking regions.

Winemakers on the island shrugged off the scorching heat on Monday, not expecting damage to their grapes, as they had a cooler-than-average spring which has delayed the growing season.

"We think it'll be mild for the rest of the week, so I don't think one hot day like this will be an issue," said Mr John Brown, winemaker at Frogmore Creek Winery.

"We're just chilling at home where it's cool inside," he said.