FLOODS are threatening to rain on the Australia Day parade in northern NSW.

Residents have been urged to swap their outdoor barbies in favour of indoor safety.

The Bureau of Meteorology says a flood watch has been issued for the NSW coastal valleys from the Queensland border to the Lower Hunter later tomorrow.

There's a greater than 75 per cent chance of major and flash flooding developing along the coast from the Queensland border to Taree, as well as in the upper Macintyre Valley in the Northern Tablelands.

The incoming weather has also prompted a warning for northern NSW residents to avoid any unnecessary travel where possible.