Rare wave clouds spotted in Tauranga

Wave clouds were spotted in Tauranga last night, making the unusual formation of clouds at least the third sighting around New Zealand in recent weeks. Photo/Jessie Kaur Irwin

A rare wave-cloud formation has been spotted in the skies above Tauranga.

The clouds, which look like a series of rolling waves, have been spotted on at least two occasions in other areas of New Zealand in recent weeks but this was the first photo of the waves above Tauranga.

The phenomenon is officially called Kelvin-Helmholtz instability, named after Scots-Irish scientist Lord Kelvin William Thomson and German physician and physicist Hermann von Helmholtz.

Jessie Kaur Irwin had been heading from Brookfield towards Bethlehem when she saw the clouds.

"It reminded me of the wave cloud over Palmerston North the other week," she said.

WeatherWatch's Phillip Duncan said the wave clouds acted much like waves in the ocean and it was often "hard to get them and hard to predict them".

"I've seen very few of them in my whole career. It's definitely not very frequent. It's pretty rare to see there here."

MetService meteorologist Ravi Kandula said Tauranga's wave clouds were a "nice example" of Kelvin-Helmholtz waves.

Mr Kandula said the phenomenon was not altogether uncommon but rarely captured.

"It was a calm night last night with a southeast wind. Aloft, that wind was travelling about 20 knots faster . . . over that layer. So it's like you have two plates moving over the top of each other and if you have liquid in between, it's got to do something. You end up with these rolling waves," he said.

"This would be happening all the time but you need cloud to make the waves, and there's not always cloud around.

"It's rare being captured so often lately. It is pretty cool."

Last month, similar wave clouds were spotted in Palmerston North, causing what MetService meteorologists said were the best example of Kelvin-Helmholtz waves they had seen.

Wave clouds were also spotted in Christchurch earlier this month.