East coast residents have been warned to stay vigilant as a severe weather system delivers a likely deluge and possible flooding.
The NSW north coast is expected to bear the brunt of wild weather as it moves across the border from Queensland on Monday, the Bureau of Meteorology says.
In the NSW Northern Rivers region, Ballina had received about 94mm of rain between 9am and mid-afternoon, while Yamba to the south had received nearly 80mm.
Rising local rivers and flash flooding were likely within the areas that received the heaviest falls, the bureau said.
Catchments within the flood-watch areas had been dry but were beginning to become wet as widespread rain and isolated thunderstorms continued in parts of coastal Queensland and northeast NSW, meteorologist Dean Narramore said.
Heavy rainfall is likely to affect regions in an area stretching to as far north as Mackay in Queensland.
"We have an upper trough combined with a really moist onshore flow and that's causing this trough system to deepen and cause widespread rain and storm activity from the central (Queensland) coast all the way down to northeastern NSW," Mr Narramore said.
"It's going to continue today, tonight and into tomorrow as this system very slowly moves south."
The weather system was forecast to move off the coast by late Wednesday or Thursday.
The NSW State Emergency Service urged residents in Lismore, Byron Bay, Ballina, Evans Head, Yamba and Maclean to monitor conditions.
Rainfall totals between 40mm and 80mm were likely in those areas on Monday, with isolated totals possible of up to 150mm.
"Currently, rain is occurring across the Northern Rivers and is expected to persist until this afternoon," the SES said.
