Heavy rain, wild surf and gale force winds are expected to hit northern NSW on the Australia Day long weekend, the Bureau of Meteorology (BoM) warns.
BoM says ex-tropical cyclone Oswald, which has already travelled 2000 kilometres south from Cape York, is tracking south and is due to hit the states north today.
In a statement, it said the wild weather would move south to the NSW mid-north coast tomorrow and Monday, with communities at risk including Ballina, Byron Bay, Grafton, Coffs Harbour and Port Macquarie.
The rainfall is expected to extend west of the Dividing Range, affecting Moree and Inverell, and south to eastern parts of the Hunter Valley, including Newcastle, BoM said.
It said gale force winds would produce high seas and damaging surf conditions.
It also said the low pressure system had the potential to cause major flooding from the Queensland-New South Wales border to the Hunter Valley.
The weather bureau forecast the rain and wind to ease on Tuesday.
Surf Life Saving NSW spokesman Dean Storey said novice surfers should avoid the ocean after the front hits and "persons intent on swimming should only do so between the red and yellow flags".