It is forecast to reach 33 degrees Celsius in Sydney city, and 40C in western suburbs.
On Sunday, a reading of 47.3C was recorded in Penrith by the late afternoon, making it the hottest temperature recorded in Sydney since 1939. It was also the hottest city on Earth.
The Australian and England cricket teams suffered temperatures in the 50s out on the field at the Sydney Cricket Ground.
England captain Joe Root was taken to hospital to be treated for severe dehydration.
