RENEE MONTAGNE, HOST:
Over the past few days, four tropical cyclones have been sweeping through the Western Pacific and the Indian Ocean, just west of Australia. One of those cyclones slammed into the islands of Vanuatu last weekend with deadly winds of 165 miles per hour. NPR's Christopher Joyce has more.
CHRISTOPHER JOYCE, BYLINE: We call them hurricanes, but a big spinning storm in the South Pacific is called a cyclone. Same deal, though - big winds, lots of rain and bad news for low-lying coastal areas. How crazy is it to have four at once? Well, it's rare.
GARY BARNES: You can just get a certain set of events that can trigger things.
JOYCE: Gary Barnes heads the atmosphere sciences department at the University of Hawaii. He said it starts with unusually warm water in the Pacific.
BARNES: Sections of it have reached 31 degrees Celsius, which is pretty darn toasty.
JOYCE: Eighty-eight degrees Fahrenheit - toasty. Then you need something called the MJO - the Madden-Julian oscillation. It's a weather system that travels from west to east across the Indian and Pacific Oceans. It brings wind blowing from the west, and there was an MGO recently. So when this westerly wind collides with the Pacific trade winds, which come from the east...
BARNES: Think of a paddle wheel on the back of an old steamer. You'd have a tendency for this paddlewheel to spin.
JOYCE: This spinning vortex sucks moisture and heat from the ocean up into the atmosphere, and that really gets things going.
BARNES: It tends to concentrate that spin, just like an ice skater pulls her arms in and starts to spin faster, and spin up to a tropical cyclone.
JOYCE: Now, it is rare to have four cyclones or hurricanes at once, but Barnes says hold off on blaming climate change. It isn't the first time there have been several at once.
BARNES: Everybody says wow, it's the end of the world, and I say it happens. (Laughter) And now it's happening around Australia and out into the West Pacific.
JOYCE: In fact, this odd Western wind may have brought the first people to Hawaii centuries ago. They're thought to have come from the Western Pacific in sailing canoes. Now, these early vessels couldn't sail directly against trade winds coming from the east, but Barnes says a westerly wind from an MJO would have been perfect. Christopher Joyce, NPR News. Transcript provided by NPR, Copyright NPR.