Dangerous swells this week mean that swimmers and rock anglers will need to take special care, weather forecasters say.

A number of large swells have pounded the east coast of Australia over recent weeks.

A fisherman drowned after being swept off rocks at the Royal National Park, south of Sydney, on Saturday.

And two rock fishermen drowned at Mosman on May 1 after one of them was washed into the water by a wave and the second man jumped in to rescue him.

The bigger swell events are tied in with the formation of intense low-pressure systems over the Tasman Sea, weatherzone.com.au meteorologist Alex Zadnik said.

These east coast lows become most frequent at this time of year as cold air from the south clashes with lingering humid air over the relatively warm waters of the Tasman Sea.

For large swells to form, a sustained period of gale-force winds over a broad area of water is required, and this is precisely what these lows bring.

Swells from an east coast low can take a couple of days to arrive, which can often catch people off guard if skies on the coast are clear and the weather is benign, Mr Zadnik said.

The biggest waves can also arrive 20 to 30 minutes apart, which makes activities such as rock fishing especially hazardous.

There is the potential in the coming week for a number of deep lows to form over the Tasman Sea, so it would be best advised to check the most up-to-date marine warnings before planning any coastal activities.

smh.com.au, AAP

Weatherzone.com.au is owned by Fairfax Media, publisher of this website.

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