Sydney - May has so far been so warm that the authorities in Sydney are keeping outdoor swimming pools open longer than usual and at least one council is reviewing lifeguard numbers to cope with late-season beach-goers.

Along with much of south-eastern Australia, the capital of New South Wales is in the midst of an autumn heatwave that is setting records, with daily maximum temperatures 5 deg C or more above average, the Sydney Morning Herald reported yesterday.

It was a similar story in Adelaide, the capital of South Australia, where last Friday's 27.4 deg C maximum was the warmest recorded for this time of year since records began more than a hundred years ago.

Tasmania's capital Hobart, with 23.9 deg C last Thursday, also set a record for this time of year.

A lack of strong cold fronts has allowed the summer heat to linger over the interior, said forecaster Weatherzone. A near-stationary high pressure system over the Tasman Sea has allowed northerly component winds to filter this heat into the Sydney Basin, it added. The high has also brought mostly sunny skies.

Weatherzone meteorologist Ben Domensino told the Sydney Morning Herald: "At this time of year, we get our rain from the passage of the frontal systems. The highs are keeping the skies clear, which is allowing those temperatures to creep up, but it's also preventing any rainfall."

The newspaper said the unseasonal warmth is causing problems for local councils and pool operators which organise lifeguard services. Volunteer lifesavers usually monitor beaches only until the end of April and many pools are often closed for the season by now.

"We're not looking at closing it in a hurry. It's purely because the overnight temperatures have been so high... I'm not losing so much heat," Mr Reece Heddle, manager of aquatic services for Randwick City Council in Sydney, told the Herald.

Weatherzone said since 1859, Sydney has only had 21 days in May where it has reached 25 deg C.

"It's been significantly warmer than average throughout the country," with only a few cool pockets on the Queensland and West Australia coast, a senior climatologist at the Bureau of Meteorology, Dr Blair Trewin, told the Herald.

Victoria's capital Melbourne is also in the midst of a warm spell. The city is expecting at least 10 days of 20 deg C weather, easily eclipsing the previous longest warm spell this late in the year of seven days, according to Weatherzone

"Typically we get about two fronts every week (at this time of year), which keep the heat away. But we're likely to be going at least a week without one coming through," Weatherzone's Mr Brett Dutschke told Melbourne's The Age newspaper.

It is bad news for farmers hoping for rains, said the newspaper.