Heavy swells will hit New Zealand on Monday and Tuesday as an area of low pressure south of the country builds up wave heights.
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"A very deep low pressure centre (926hPa) over the ocean near 69S has generated heavy swells," MetService meteorologist Andy Best says on Twitter.
"As this wave model shows, the pure swell component (without the wind wave component) will affect areas east of the South Island, especially the Chatham Islands in the next 24hrs."
The lower South Island will be affected too, particularly Stewart Island and Fiordland.
The swells are generated by wind blowing over the sea for a long time.
"Persistent winds for long periods of time will develop swell waves. That's the swell we normally see arriving on our shores from low pressure systems," Best told Newshub.
MetService forecasts a period of 18 to 20 seconds between the swells, which will range between four and six metres in height. This could be significant enough to affect boats and ships, Best told Newshub.
Apart from heavy swells kicking things off, the forecast is for mainly fine, settled conditions over New Zealand through much of this week.
"We expect the winds to drop off over the bulk of the country, although a strong westerly flow does impact Stewart Island and the Southland and southern Fiordland coasts during Wednesday and Thursday," MetService says on Facebook.
"Over Northland we also see brisk southeasterlies maintained between the developing ridge and the low pressure area well north of the country."
Newshub.
