New South Wales capital city has already reached 37.1 degrees as of 12pm EDT, which makes it Sydney's hottest Australia Day since 1960. 

Sydney Airport has recorded 40.2 degrees as of 1pm EST, with western areas expected to get even hotter. The current heating has led to both locations having their hottest day since 29th November last year.

Sydney has also achieved its hottest spell in 10 years, averaging a maximum of 33.5 degrees for the last 5 days (most of western Sydney west from Bankstown has been averaging 36-39 degrees but had a hotter 5-day spell last summer).

The very hot airmass is being drawn from inland across the region ahead of a low pressure trough moving in from the west.

Image: Temperature in degrees celsius at 2 m height for 3pm EDT. Displayed using the ACCESS-C model.  

The heat will remain until later in the evening, with a weak southerly pushing through the city overnight. However, clouds are likely to trap some of the heat, keeping temperatures in the low-to-mid 20's until Wednesday morning.

Tomorrow will be a stark contrast, with a top of about 26 degrees in the east and 25 degrees in the west and the potential for light showers from the afternoon/evening.