Lismore has recorded its first flood in nearly two years, as the level at the Lismore gauge rose above 4.2 metres to 4.21 at 8:42 this morning.

Yesterday's heavy rainfall in the catchments (Goonengerry 230mm, Corndale 180mm, Repentance 226mm, Terania Creek 168mm, Dunoon 186mm, Nimbin 123mm) took a long time to reach Lismore as the rainfall eased last night.

The last minor flood was recorded on the 24th of October 2022 when the gauge reached 6.64 metres, under the 7.2m Moderate Flood Level.

Sarah Scully, a senior meteorologist with the Bureau of Meteorology said the persistent rain is being driven by a combination of three different atmospheric factors.

"We've got an onshore flow that's bringing a lot of moisture from the tropical Pacific Ocean from Queensland and northern New South Wales. And then we've got a coastal trough near the state border that's enhancing that rainfall. And then on top of that, we've got an upper-level low pressure system over Queensland, and that's helping to amplify or create really unstable conditions, resulting in these really extensive and persistent rainfalls.

"This entire system is quite slow-moving, and the rain is expected to continue throughout the day, particularly about the Queensland coast, and then we start to ease off during Wednesday morning, and then clearing by Thursday, as the system moves out over the water."

Lismore was forecast for a further 5 to 25mm today and 15 to 50mm on Wednesday before the rain begins to clear on Thursday.

While the gauge is at 4.22m at 9:41am, it is expected to peak near 4.50 metres early this afternoon. The Bureau is saying renewed rises are possible from Wednesday with forecast rainfall as we have saturated ground in the Northern Rivers.

To stay up to date with the weather forecast and the radar, click on Weather & Travel on the Lismore App or the Lismore App website www.lismoreapp.com.au. The BOM's warnings are available via the weather button.