The first major heatwave of the summer will start to lap Sydney’s suburbs on Wednesday and is unlikely to fully recede for another week.
Sydney will be spared the worst of the heat for most of the coming eight days as cooling sea breezes are expected to keep the lid on temperatures on the worst extremes.
Western suburbs, though, will start to swelter from Wednesday with the mercury such as around Penrith likely to nudge 40 degrees.
It is forecast to exceed that on Thursday and again next Tuesday and possibly Wednesday.
Much of the continent will bake during this period, particularly north-western NSW and south-west Queensland. There the hot spell is likely to be the worst for December in eight years if not longer, Brett Dutschke, a senior meteorologist from Weatherzone, said.
“It’s unusually intense and long lasting for this time of the year,” Mr Dutschke said.
Parts of southern Australia are broiling on Wednesday, with Adelaide already reaching 39 degrees and Melbourne headed for 37 degrees.
Onshore winds, though, will keep Sydney – or at least places close to the harbour or the coast – to a more pleasant 29 degrees, the Bureau of Meteorology predicts.
Hottest still to come
A couple of weak cool changes will provide some relief for those near the coast on Friday and Sunday, before the heat starts to build again for the NSW capital.
“The following three days at least [from Sunday] will be when we feel it – that’s when the nights are going to stay warmer for longer compared to the next couple of nights,” Mr Dutschke said.
“It looks like there’s a good chance that next Wednesday will be our hottest day [of the current spell] just ahead of a stronger, cooler change,” he said.
Where possible people should take advantage cooler evenings to open windows to help buildings lose some of their build-up heat.
A slow-moving high pressure in the Tasman Sea and a similarly stagnant low over north-western WA are combining to push the heat over central Australia into the south and south-east.
The Sydney metropolitan region has a “very high” fire danger rating for Wednesday, with worse expected on Thursday.
“It looks like the fire risk will be greatest [for Sydney] tomorrow, but it’s not looking particularly bad,” Mr Dutschke said, adding that next Wednesday “could rival that.”
By Saturday, the three-day heatwave forecast has at least half the country in a low-intensity or even severe heatwave, the bureau predicts. (See chart below.)
Inland regions likely to have extended bouts of heat include Bourke in north-western NSW. The town can expect at least seven consecutive days of 40 degrees – the first occurrence at this time of year since 2009,” Mr Dutschke said.
If they achieve more than seven such days, which is possible, it would be a 23-year high for this time of year.
Thursday has the potential to be Penrith’s hottest December day in more than 20 years, likely reaching 42-43 degrees, Mr Dutschke said.
It did, though, notch an even more sizzling 44.9 degrees in November 2014.