Waves off New Zealand's East Coast could reach up to 10 metres in the coming days as a "rapidly rising" swell approaches from the south of the country.
Heavy swell warnings have been issued for the Wellington and Wairarapa coasts, with dangerous conditions expected to peak on Tuesday.
Wellington's coastline from Cape Terawhiti to Turakirae Head faces combined waves of 7-8m around midday Tuesday, while the Wairarapa coast from Turakirae Head to Mataikona is forecast to see even larger combined waves of 9-10m late Tuesday morning.
MetService said combined wave heights in eastern offshore waters could reach or exceed the height of the Ohakune Carrot (7.5m).
"Hazardous conditions mainly for offshore vessels operating in exposed eastern waters."
MetService meteorologist Devlin Lynden said the swell is being driven by a deep low pressure system sitting to the south of the country, generating very strong southwesterly winds.
"There's a deep troughing to the south of the country — a deep low pressure system — which is driving very strong southwesterly winds in the area," he told 1News.
Two key factors were combining to produce the dangerous conditions: wind speed and fetch — the distance over which a swell can build. In this case, the southwesterly swell has had virtually the entire Southern Ocean to grow across.
"The combination of large fetch and strong winds is what's creating these significant swells," he said.
The most affected areas would include offshore waters and the Chatham Islands, as well as coastal stretches along the southern Kaikōura coast, parts of Banks Peninsula, and the Catlins coastline south of Dunedin — all expected to bear the brunt of the swell over the next 24 to 48 hours.
Lynden said what makes this event particularly notable is how fast conditions will deteriorate.
"We are talking about rapidly rising, which is not a wording we use commonly, and it really reflects how quickly the swells are likely to rise in the affected areas."
Recreational boaties were urged to exercise extreme caution, particularly around harbour entrances and bar crossings, where large swells significantly increase risk.
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