Gabrielle is already driving incredible waves near New Zealand – with some at the cyclone system’s centre reaching the equivalent height of a four-storey building.
MetService is warning people to be wary of higher tides and big seas over coming days, with waves on the Wairarapa coast potentially reaching 6.5m high on Tuesday morning.
Off the North Island’s north-east coast, Niwa reported waves could climb to 5m to 8m high at times over Monday and Tuesday, with coastal flooding and inundation likely.
On Sunday afternoon, models indicated maximum wave heights near the cyclone’s centre, north of New Zealand, had topped 12m.
Meanwhile, physical data direct from wave buoys stationed off the coast of Whangarei showed maximum wave heights close to 10m high – and significant wave heights of just over 6m.
Maximum wave height measured the largest single wave recorded, from peak to trough.
Significant wave height, meanwhile, was the average measurement of the largest third of waves - something that corresponded well to our own visual estimates.
University of Auckland coastal geomorphologist Associate Professor Murray Ford, who’s been closely watching observations throughout the day, said those values would likely grow higher as the system neared our shores.
“Models are suggesting wave heights aren’t supposed to peak off Whangarei until about midnight tonight – so it’s predicted to get higher.”
The huge waves were reflected the system’s massive wind speeds – but also that it had a large area of water for winds to blow across, or what’s called fetch.
“You’ve got an easterly wind blowing across a long fetch.”
Ford said tide gauge data from North Cape was also showing what’s called the inverted barometer effect, which occurred when very low air pressure forced the sea to rise.
“The water there is already about 30cm to 40cm higher than it was during the last high tide, because of the low pressure.”
According to the World Meteorological Agency, the largest wave ever recorded by a buoy was a 19m-high beast rolling in the North Atlantic Ocean between Iceland and the UK, in February 2013.
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