Why is NZ so windy? The roaring forties explained
New Zealanders shouldn’t be so surprised how often it’s windy here, says WeatherWatch.co.nz
"After all, we’re basically a few mountainous islands stuck partially in the Roaring Forties," says head forecaster Philip Duncan.
He says to many people, that doesn’t mean a lot and doesn’t clearly explain the set up, so "we’ll give it a go".
"No offence to our small country but…we are very small! We look huge compared to our island friends to the north, but compared to Australia, North America, Asia, Europe, Africa, South America…we are tiny. Our small size means the weather basically barrels over the top of us."
The Roaring Forties
This is the belt of wind at latitude 40 (south to latitude 50) over the Southern Ocean that sailors centuries ago named.
Unlike the northern hemisphere, which has a lot of land at this latitude, the Southern Hemisphere in the 40s is mostly ocean with just tips of land – like Tasmania, says Philip,
"New Zealand’s South Island and the very southern portion of South America the only areas that briefly jut out into this area.
"With a lack of land to slow things down the wind whips up across the sea, fuelled by storms these strong winds swirl around Antarctica quickly."
These westerly winds blast over the South Island and the lower portion of the North Island.
"In fact, the Roaring Forties stops northwards at about Whanganui. North of that you’re outside of the Roaring Forties.
"So when you’re a few islands in the middle of no where, surrounded by ocean and more than half of your country juts out south directly into the Roaring Forties belt of strong westerlies, it’s no real surprise that NZ keeps getting shots of wind when we think it should be calmer."
Philip says our mountains make it worse and better.
"New Zealand’s mountains have a giant impact on our weather. They create floods and droughts by holding up rain clouds in one region and blocking rain from reaching the next region.
"This process also makes for some spectacular high clouds and ‘UFO’ clouds in our east and central parts."
The winds coming over the Southern Alps and main ranges also speed up – giving NZ those gale nor’westers which are so well known in Canterbury or Wellington.
These same mountains and ranges also make other areas very calm and sheltered, like Nelson and Bay of Plenty, says Philip.
"Inland areas away from the sea are often much calmer too, like Taumarunui in the north and Alexandra in the south."
NZ HAS THREE MAIN WIND TUNNELS:
• Foveaux Strait
• Cook Strait / Wellington
• Auckland City – which is just over 1km wide at its narrowest point between Tasman Sea (west) and Pacific Ocean (east).
These three areas can often have windy weather lingering longer all year round (especially coastal areas or exposed areas) simply due to the effect the Roaring Forties has around NZ and surface winds looking for the path of least resistance.
"A bit like how water flows through the lowest points on land, like valleys, the wind flows through our wind tunnels between islands like the Straits, or at our lower/narrow points like Auckland, and to some degree Manawatu and Wairarapa partially fuelled by the Cook Strait tunnel but also the low gap in the Manawatu Gorge."
The closer you get to Antarctica the worse those winds get and the bigger those Southern Ocean storms are, says Philip.
"The creative names given by sailors centuries ago clearly sums up just how terrifying this part of the planet is. There is no where else on earth that is anything like the Roaring Forties, Furious Fifties and Screaming Sixties.
"And remember, lil ol’ New Zealand has half of itself parked in those Roaring Forties forever. (well, maybe in millions of years NZ might have moved on!).
A DIFFERENT PERSPECTIVE:
"On maps North is always straight up. But if we flip the map of New Zealand so that “up” looks directly towards where our predominant wind (W to SW) comes from it paints a different picture in your mind about where we sit on the planet. It helps understand why we get so many windy events, sometimes for weeks – even months – at a time."
WeatherWatch.co.nz often says NZ only has a two month winter and a two month summer – the other eight months are windy west to south west times – or an extended spring and autumn if you like.