A total fire ban has been declared in the Sydney basin as the city braces for an unseasonable scorcher today.

The Bureau of Meteorology this morning revised upwards its forecast maximum temperature in Sydney to 36 degrees, 4 degrees higher than original expectations.

Strong west to north-westerly winds, up to 50km/h will accompany the heat before a southerly change moves through this afternoon.

The Rural Fire Service acted quickly on the bureau's advice, declaring a total fire ban across the Greater Sydney, Greater Hunter, Northern Slopes and North Western regions.

Temperatures are expected to drop by more than 10 degrees tomorrow, with a shower or two and a top of 24 degrees expected.

The total fire ban will be in place until midnight today.

- with AAP

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