There are signs that the natural phenomenon is developing in the Pacific, but what exactly is it?
It was a close-run thing, but Sydney has just missed out on recording its hottest November day on record.
On Friday afternoon, the mercury peaked at 40.9C in central Sydney, just 0.9C shy of the all-time high of 41.8C set in 1982.
Temperatures were higher at the international airport, where a maximum of nearly 43C was reported.
At one point a westerly wind, bringing hot air in from the interior, caused the temperature to jump by 10C.
This is the third day that temperatures have reached at least 12C above average.
The hot weather has raised the risk of wildfires. There have been several small fires across the New South Wales, and firefighters have warned that strong winds, gusting up to 90kph, and very low humidity, will exacerbate the situation.
There are bans on lighting fires in many parts of the state, and farmers were requested to cease harvesting to reduce the fire risk.
The current El Nino is expected to remain well into the autumn and El Ninos tend to bring hot, dry conditions to much of the country.
There is also evidence to suggest that there will be an increased frequency of heatwaves.
A recent study published in the Journal of Geophysical Research showed that strong El Ninos (this one is comparable to the infamous one of 1997-8), bring more heatwaves to northern and eastern Australia.
The study found that the risk of a ‘severe’ season for heatwave frequency was twice that of a summer where El Nino and its ‘sister’ La Nina were absent.
Although there may be more heatwaves to come for Sydney, this one will come rapidly to an end.
In the space of 24 hours, Sydney’s maximum temperature is expected to drop by 20C, to slightly below the late November average.