Sydneysiders are having a scorcher with the mercury set to hit 40 degrees in the west and no reprieve until midnight.
The Bureau of Meteorology's Agata Imielska said parts of west Sydney would top 40 degrees on Monday, with the east set to reach 36 degrees around 5pm.
The sea breeze would keep east Sydney cooler than the west throughout most of the day before westerly winds heat things up late in the day, Ms Imielska said.
A cool southerly isn't expected to reach the city until late.
"We are expecting the proper southerly change to come through around midnight, so that's really when we'll see temperatures dropping quite significantly," Ms Imielska said.
Parts of NSW's north are expected to reach the high 30s, with Tamworth set for a maximum of 38 degrees.
The Hunter region was also expected to reach mid to high 30s on Monday.
However, conditions should be significantly cooler for most of the state on Tuesday, with a cloudy day predicted for Sydney and a 30 per cent chance of a shower in the early morning and again in the late evening.
Australian Associated Press