Massive wave south of NZ believed to be a Southern Hemisphere record

Thursday, 10 May 2018

Simulation showing the significant wave height to the south of New Zealand during the storm overnight Tuesday.

A massive wave measuring 23.8 metres has ripped across the Southern Ocean.

While it was thought to be the largest wave measured in the Southern Hemisphere, it was probably dwarfed by others during the storm that generated it.

Waves over 25m were possible during that event, overnight Tuesday, MetOcean Solutions senior oceanographer Dr Tom Durrant said.

The wave was measured at a wave rider buoy at Campbell Island.

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A monster wave in the Southern Ocean, south of New Zealand, was likely the largest measured in the Southern Hemisphere. This file photo shows a Southern Ocean storm in 2016 photographed from offshore patrol vessel Otago.

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'The Southern Ocean is a unique ocean basin and is the least studied despite occupying 22 per cent of the global ocean area,' Durrant said.

'The persistent and energetic wind conditions here create enormous fetch for wave growth, making the Southern Ocean the engine room for generating swell waves that then propagate throughout the planet - indeed surfers in California can expect energy from this storm to arrive at their shores in about a week's time.'

The monster wave was the perfect example of waves generated by the easterly passage of a deep low pressure system with wind speeds above 120kmh, Durrant said.

It was particularly interesting that the speed of this week's storm appeared to match the wave speed 'allowing wave heights to grow dramatically as the system tracks eastward'.

Reasons for thinking the measured wave wasn't actually the biggest during the storm included the wave forecast , which showed larger wave conditions just north of the buoy location.

Also, the buoy was solar-powered and to conserve its battery waves were sampled for just 20 minutes every three hours, Durrant said. 'It's very probable that larger waves occurred while the buoy was not recording.'

The buoy also measured the significant wave height - approximately the average of the highest third of the measured waves - during the storm at 14.9m. That was a record for the Southern Ocean but well under the world record of 19m measured in the North Atlantic in 2013.

The Southern Ocean wave studies are a collaborative project with the Defence Force, Defence Technology Agency and California-based company Spoondrift.

As part of the programme, MetOcean - a wholly-owned subsidiary of MetService - has deployed seven instruments to collect wave data, using one moored and six drifting buoys.