The Bureau of Meteorology said NSW's north coast would bear the brunt of the wild weather as it moved across from Queensland, where 150mm was possible in southern regions on Monday.
Meteorologist Helen Reid said there were forecast falls of 50mm to 70mm north of Coffs Harbour and "localised falls exceeding 120mm are possible".
Flood Watch issued for catchments in the Northern Rivers. Isolated minor flooding possible in Tweed, Richmond & Wilsons Rivers from Monday due to forecast rainfall. Moderate to heavy rainfall possible. Stay up to date with warnings at — Bureau of Meteorology, New South Wales (@BOM_NSW) https://t.co/4UHA6k1BNE pic.twitter.com/QiRVk0r4njAugust 11, 2024
Flash flooding was also possible, especially in the Northern Rivers region, Ms Reid said.
"There could be warnings for heavy rainfall issued today," she said.
The weather system was forecast to move off the coast on Wednesday.
The NSW State Emergency Service urged residents in Lismore, Byron Bay, Ballina, Evans Head, Yamba and Maclean to monitor conditions.
It said rainfall totals between 40mm to 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," NSW SES said in a statement.
The agency said the heavy rain was being caused by a trough of low pressure in the area with a "moist and unstable airmass".
14°C