A high of 31 degrees was reached in Sydney's CBD about 2pm (AEDT) on Wednesday, making it the hottest Australia Day on record in the city since a high of 32.1 degrees was recorded in 1991.

In the western suburbs the temperature had reached 34 degrees by 2pm (AEDT), which was below the forecast peak of 42 degrees predicted for Penrith.

But the bureau said the temperature in the west was continuing to rise.

"Penrith hasn't peaked yet - it's still rising," a bureau spokeswoman said.

The hottest Australia Day on record for Penrith was 42.3 degrees in 2003.

"I'm not sure it will get as warm as we expected in Sydney," the spokeswoman said.

"The temperature dropped a couple of degrees at lunchtime (due to) a southeasterly sea breeze."

source: News.com.au