Sydney's break from late-spring heat will be short-lived with slow moving high-pressure systems likely to steer inland warmth into Australia's south-east this week and next.
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The city's maximum will climb from an expected 25 degrees on Tuesday to 29 degrees on Wednesday although western suburbs, without the benefit of cooling sea breezes, will likely warm to the mid-30s.
Thursday, though, will see temperatures ranging from 34 degrees in the city to 38 in the west as a hotter air mass sweeps in, said Tristan Meyers, a meteorologist with Weatherzone.
While models give varying estimates of the timing and strength of an expected southerly change, Thursday will likely fall well short of the 40.9 degrees - Sydney's second-hottest November day - set last Friday, Mr Meyers said. The city's average November top is 23.6 degrees.
Temperatures have been well-above average for November in central and northern Australia, creating a pool of heat available to be "squirted" into southern regions, Andrew Watkins, head of climate prediction services, at the Bureau of Meteorology, said.
Meteorologists say another build-up of heat is likely in the first few days of December, bringing a warm start to summer.
"It will be warm [for Sydney] but nothing like what we had [last week] - an extreme heating event," Mr Meyers said.
The bureau is predicting a warmer-than-average December overall for most coastal regions, including for Sydney. (See chart below.)
El Nino influence
"This summer is looking to be warmer than usual," Dr Watkins said. "Things are quite dry inland with dry soils, typical of an El Nino year, and slow-moving high pressure systems."
Temperatures tend to be "a bit more super-charged" under the relatively cloudless skies over the inland, he said.
For many areas, though, the unusually warm conditions should back off a little by January, the bureau predicts.
The El Nino is among the three strongest on record. During such events, wind patterns in the Pacific change, generally reducing rainfall over the western Pacific and increasing it in the east.
According to the UN's Office for the Coordination of Humanitarian Affairs, water shortages are becoming severe among Australia's South Pacific neighbours.
About 67,000 people are receiving water deliveries in Fiji, 40 per cent of Vanuatu's communities are expected to run out of safe drinking water in the coming month, and parts of the Solomon Islands are reporting damage to 70 per cent of crops from the extreme heat, the UN said.
