The predicted conditions have prompted surf lifesavers and the Bureau of Meteorology to issue a warning to be careful in the water.

Surf Life Saving NSW said the deceptively powerful conditions are expected to last until at least Saturday, with swimmers, surfers, rock fishers, and boat users all urged to check the latest forecast.

The southerly swell will develop on Tuesday night, with a predicted peak of around 3.5 metres as it travels up the coast.

Additionally there will be a long period swell of up to 10 seconds in most parts of the coast, which is particularly important for rock fishers to be aware of as they get on and off exposed platforms.

NSW Operations Manager Andy Kent has urged the public to take the warnings seriously.

“The best advice we can give people is to be aware of their environment and the changing conditions. Take the time to study a recent weather forecast before heading out and let others know what your plans are,” Mr Kent said.

“A great first point of call is the BeachSafe Website which provides an overview of all the patrolled beaches and also any closures.”

Mr Kent also urged all beachgoers not to take any unnecessary risks.

“The drownings that we have seen over summer reinforce the importance of swimming at a patrolled location and we strongly encourage everyone thinking about engaging in an activity on or around the coast to make that extra effort and go where lifeguards are,” he said.