Weather forecasters are warning the public to take special care on or near beaches in western parts of the country over the long weekend.
A deep low in the Southern Ocean near Antarctica is expected to generate sea swells that could reach nine metres between the Far South and the West Coast tomorrow.
They say it could pose a threat to fishers, surfers and others, particularly on the South Island's West Coast, where it is also likely to exacerbate coastal erosion.
Meteorologist Rob Kerr told Morning Report a big low southwest of Fiordland would gradually track eastward and bring the large swell.
Nine metres will be the peak wave size this weekend, with five to six metres around the Fiordland coast. North of Greymouth will see four to six metres, Kerr said.
"Because this swell is coming from far away it has quite a long period," he said. "Some of the waves will have a tremendous amount of power and progress much much further inland."
Meanwhile, a rain band is moving up the north bringing with it a chance of thunder storms.
People in Fiordland and Westland are advised to keep up to date with the latest forecasts as fronts continue to bring bursts of heavy rain to those areas.