Surfers get ready.

Large waves are expected to hit the lower West Coast of the South Island mid-week, when waves up to 10m are forecast in the Southern Ocean, and reaching up to 4m high along the coastline.

The biggest waves will be offshore, but the best places for surfers are along the coastline south of Haast and Fiordland on Tuesday and especially Wednesday, according to Niwa principal forecasting scientist Chris Brandolino.

"If you are looking for big waves, you want to go south - the lower West Coast of the South Island."

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Hokitika and Greymouth could also expect waves up to 3.5m along the coast, and Jackson Bay is likely to reach 4.5 to 5m. Campbell Island and the Auckland Islands will get waves up to 7m high.

Competitors in the Volvo Ocean Race will also experience choppy conditions during the next few days as they race from the East Cape to north of Chatham Islands.

"It's not the same packet of waves making surfers smile, but the choppy waters will be coming from the east. It will be a bit of a head chop."

"There will be some beefy waves," Brandolino said. "Three-four metre waves will be impacting them between now and Wednesday."

Along with the big waves, the far south should brace for a big drop in temperatures come Wednesday.

Invercargill will experience the most extreme changes, going from a maximum high of 26C on Tuesday to a maximum high of 16C on Wednesday along with a howling southerly and rain showers.

"What an awful change. They need the rain, so that will be good for them, but the wind chill will make it feel even colder - the effect of wind and the air temperature barely reaching 16C will make it feel probably below 10C," Brandalino said.

Dunedin will also get a cold snap, going from a high of 27C on Tuesday to a high of 19C on Wednesday.

The big chill will only impact the South Island. Wellington will only experiencing a slight drop of 2C from its high of 25C on Tuesday compared with Wednesday.