Sydney is in for another scorcher on Thursday with the potential for 40 degrees over much of the city ahead of a gusty cool change from the south.
Sydney weather: Humans and animals beat Thursday heat
Animals at Taronga Zoo are given watermelons and ice blocks to stay cool as temperatures soar to around 40 degrees in Sydney on Thursday.
The Bureau of Meteorology is forecasting a top of 38 degrees for the city - lifting its earlier prediction by 3 degrees - with 41 expected in Liverpool, Penrith and Richmond.
The city could top 40 and western suburbs as much as 43 degrees if the winds turn offshore before a cool change, Ben McBurney, a meteorologist with Weatherzone, said.
The cool change is unlikely to reach the city until 5-6 pm, and will bring "quite a drastic change" in temperatures and rain when it does arrive, said Jake Phillips, another bureau forecaster.
Before then, the city could get "a touch hotter" than the 38 degrees predicted by the bureau, bringing it closer in line with hot spots in Sydney's west. "It looks like we won't get a sea breeze" ahead of the change, Mr Phillips said.
The heat has been building up over inland regions for several days, with 46 degrees recorded on Wednesday at Hay in the Riverina.
A range of towns, including Ivanhoe, had their hottest day in three years on Wednesday, while Wilcannia was noted by the Weather Underground website as the world's hot place on Tuesday with 45.3 degrees.
What's El Nino got in store for 2016?
The giant 2015 El Nino in the Pacific is at or nearing its peak, but it will be months before the world's weather engine takes the heat off Australia.
Despite the heat, the fire danger for the Sydney metropolitan area will remain only low to moderate on Thursday, the Rural Fire Service said. The north western, lower central west plains and the southern slopes are the only fire districts with a "very high" fire rating.
The southerly cool change on Thursday is likely to be a "true buster", dragging temperatures down by 15 degrees or more in a short time.
It is also likely to bring gusts of as much as 80 km/h to parts of the coast as well as thundery showers that will tend towards rain by the evening, Mr McBurney said.
The rain is likely to persist into Friday with widespread falls of 15-30mm from Sydney to the Hunter, and more than 50mm over parts of the ranges, he said.
The change will lower maximum temperatures before they start to climb back towards the 30s or higher for Sydney early next week.
"The air mass won't be nearly as hot as this one," Mr McBurney said.
The last time Hay was as warm as Wednesday was in January 2013 when the mercury climbed to 47.9 degrees, said Agata Imielska, a senior climatologist at the bureau.
"Generally we have somewhere in NSW reach 46 degrees in January every one to two years," said Ms Imielska. "So this heatwave is the type of heatwave or temperature peak that we see most summers."
"The years that tend to fail reaching 45 degrees are La Nina years," she said, referring to the Pacific climate pattern that sees increased rainfall over much of Australia - the reverse of the current El Nino event.
Sydney's hottest day in records going back to 1859 came in January 2013 when the temperature in the city reached 45.8 degrees.