Tuesday, 12 November 2013

Why typhoon Haiyan caused so much damage

The deadly typhoon that swept through the Philippines was one of the strongest ever recorded. But storms nearly this powerful are actually common in the eastern Pacific. Typhoon Haiyan's devastation can be chalked up to a series of bad coincidences.

Typhoons — known in our part of the world as hurricanes — gain their strength by drawing heat out of the ocean. Tropical oceans are especially warm, which is why the biggest storms, Category 4 and Category 5, emerge there. These storms also intensify when there's cool air over that hot ocean.

"The Pacific at this time of year is very ripe and juicy for big typhoons," says Kerry Emanuel, a climate scientist at the Massachusetts Institute of Technology. "Once or twice a year we get a Category 5 typhoon out there."

"But it's a great rarity, fortunately, that a storm just happens to reach peak intensity when it's making landfall. And that's what happened in this case."

As it approached one large island in the Philippines, the storm pushed up into a broad bay. That created a 13-foot storm surge that caused widespread devastation at the head of that bay, in the city of Tacloban. Typhoon Haiyan struck the Leyte Gulf, in the Philippines, nearly dead-on, creating a 13-foot storm surge that funneled water into Tacloban city.

Typhoon Haiyan struck the Leyte Gulf, in the Philippines, nearly dead-on, creating a 13-foot storm surge that funneled water into Tacloban city.

Mountains also wring rainwater out of storms like these. And then there's the wind.

"So we had a triple whammy, of surge, very high winds and strong rainfall," Emanuel says.

Super Typhoon Haiyan could be the strongest on record, but scientists can't say for sure because they don't have direct measurements of the wind speed. Hurricane scientists usually fly into storms heading toward the United States to measure wind speed and barometric pressure. And the U.S. Navy used to do that for storms in the western Pacific. But Emanuel says budget cuts ended that practice decades ago.

"Since then, we've had to rely on satellites, mostly, to estimate typhoon intensity," he says. "And satellites are very good at detecting the presence of typhoons but they're not so great when it comes to estimating how strong they are."

Scientists at the U.S. Navy/Air Force's Joint Typhoon Warning Center infer that Haiyan produced sustained wind speeds of around 190 or 195 mph at its peak. John Nielsen-Gammon, the Texas state climatologist at Texas A&M University, says gusts blew up to 230 mph, which is as fast as a speeding race car.

YouTube "Imagine instead of having just one car, imagine millions of raindrops and debris moving at the same speed past you, and you're trying to stand in the middle of it," Nielsen-Gammon says. "That's the kind of force such a hurricane can generate."

The strongest hurricane or typhoon winds on record were from Camille, which struck the U.S. Gulf Coast in 1969. But its 190 mph winds don't tell the whole story. The diameter of the storm matters as well.

"Camille was a very small storm, maybe about one-fifth the size of Haiyan," he says. "So it caused a lot of devastation but over a relatively limited area."

To find out whether Haiyan had record-breaking winds, scientists may turn to amateurs for information.

"Any major storm will attract storm chasers, and Haiyan was no different," Nielsen-Gammon says. "So there were people who traveled to Tacloban specifically to get footage of the storm, and they took along some instruments. So we'll probably get some data out of that."

Of course, that number is only one way to measure the overall severity of a typhoon. The mounting death toll will be another.

And climate scientists like Nielsen-Gammon and Emanuel say that as the planet continues to heat up, so will the oceans. And that means there will be more energy available for storms — and likely more Class 4 and 5 typhoons.

Tuesday 12 November 2013



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