Parts of the South Island are expecting “monster” swells over the next 24 hours with waves up to 10m offshore.
MetService forecasts show where the large southern swell will be strongest, with combined wave heights of 8m to 10m in offshore waters around Fiordland, Southland and Stewart Island.
Combined waveheight includes both the underlying swell and waves generated by the wind. When these waves combine, they can produce seriously rough conditions at sea.
MetService meteorologist Alec Holden said it was not unusual to see big swells this time of year – but they were not often this big.
“This is definitely in the upper echelon of what I’ve seen.”
For context, 10m is about the height of a three-storey building – or nearly one-and-a-half times the height of Paeroa’s 6.8m L&P bottle.
MetService marine forecast for big swells around Fiordland, Southland and Stewart Island. Photo / MetService
“Swell is generated by wind energy getting put into the ocean through consistent, strong winds over a given area,” Holden said.
“In this case, the southwesterlies have been brewing over the Southern Ocean for a very long time. So a lot of energy has been put into the water and that’s finally reached us here in New Zealand.”
In some southern areas, the swells will produce sizeable waves along the coast.
“They do cause concern. Coastal erosion, specifically, potential inundation if they arrive at the same time as a high tide,” Holden said.
“In this case, it would be best to check with your local council website, with regards to if there is anything that locals need to be aware about for themselves.
“It’s also a danger for those attempting to leave or return to harbours.”
Conditions are expected to ease on Monday.
“As the swell travels north, it’s become detached from the southwesterlies that generated it in the first place, so they do dissipate as they move northwards,” Holden said.
