Surfers tackle the swell at Main Beach and Clarkes Beach in Byron Bay on December 2019.
Surfers tackle the swell at Main Beach and Clarkes Beach in Byron Bay on December 2019.

What you need to know about the weather this week

DANGEROUS swell of up around four metres, combined with high tides and possible coastal erosion, localised thunderstorms, locally heavy rainfall and possible flash flooding is the Northern Rivers weather forecast for Thursday and Friday.

Bureau of Meteorology's duty forecaster Helen Kirkup said Northern Rivers' current weather is the result of a trough sitting off the coastline of NSW, bringing storm activity and rainfall, plus a second trough that is located inland.

"This leads to a really unstable atmosphere and huge amounts of moisture," she said.

"On Friday it will be reasonably similar again in terms of rain.

How tropical cyclone Uesi will affect Northern NSW

"We have tropical cyclone Uesi, and depending exactly where that tracks, it will not impact the Northern Rivers in terms of rain, but it's likely to produce big swells and hazardous surf, with late Friday expecting swell over four meters," the meteorologist said.

Stay away from the coast

Ms Kirkup said expected high tides and large swell may mean the risk of heightened coastal erosion, with big easterly swells and very dangerous surf conditions for the Tweed, Byron and Ballina areas.

The large swell could impact the southern part of the Northern Rivers, including Evans Head and nearby coastal areas for longer.

"It looks like the biggest swells will be registered from Byron Bay and south, but it will stick around for longer in areas like Wooli and Woolgoolga (south of Grafton)," she explained.

Coastal areas can expect murky, foamy waters for the foreseeable future, according to Ms Kirkup.

"It's not unusual that the day after really heavy rain all sorts of stuff gets picked up and dumped in the ocean, specially if there hasn't been any rain for a while."

It's going to be sticky as humidity skyrockets

Another feature of the week will be high humidity levels with tropical moisture lingering.

"Because it's a warmer air mass it holds much more water. It's like you are in Singapore and it's been around for about six days now, and it's going to stay that way for anther few days."

When will these crazy conditions ease?

The meteorologist said the forecast for the weekend is "much calmer".

"There will be some showers around but it will be more like a 50 per cent chance rather than a 90 per cent chance.

"During the weekend and into next week there will be a lot of moisture around but it looks less of a chance of heavy rainfall."