November 12, 2013 | 12
Breaking news can sometime include mistakes, and breaking news emerging from disaster areas can be fraught with errors. Journalists try to do follow-up stories to correct facts, and until then, other journalists reporting on the same event often resort to general language to cover the vagaries. So it has been with Typhoon Haiyan. Stories in the past several days have consistently called the event “one of the strongest storms in history.” Well, here’s what we know with a little hindsight and expert commentary.
Haiyan is the strongest storm to ever make landfall, according to Jeff Masters, director of meteorology at Weather Underground, a Web site often quoted by the best weather experts. Masters knows severe weather data better than anyone I’ve encountered, and his blog is filled with fascinating facts. The “strength” of a cyclone, typhoon or hurricane—they’re all the same storm, just different names used in different parts of the world—is determined by the top speed of sustained winds, not gusts. According to Masters, Haiyan had sustained winds of 190 to 195 mph when it struck the Philippines, making it the strongest cyclone ever at the time of landfall.
It was also the fourth strongest cyclone ever recorded, according to the Joint Typhoon Warning Center in Hawaii. Three others had higher sustained winds while out at sea, then weakened before hitting land: Typhoon Nancy in 961, with 215 mph winds; Typhoon Violet in 1961, with 205 mph winds; and Typhoon Ida, in 1958, with 200 mph winds. All three eventually hit Japan. The second strongest storm at the time of landfall was Hurricane Camille, which struck Mississippi bearing 190 mph winds.
It’s important to realize that even a modest rise in speed can cause a huge increase in damage, because the power in wind increases as the cube of speed; a wind that is twice as strong delivers eight times as much power. Camille obliterated towns and the landscape. If the same storm hit Miami or New York City today, Masters says, the damage could be half a trillion dollars. Building codes in southern Florida require the highest wind resistance in the world, Masters says, yet the rules have only been in effect for a couple of decades and many buildings are older than that.
Despite destructive winds, a storm’s surge—the height of the sea above the tide—can inflict the heaviest damage and kill the most people. Storm surges vary a lot even among the most powerful storms, because the rise in ocean water is driven not just by the wind speed but how long high winds are sustained, how fast the storm moves forward, whether a storm makes landfall during high or low tide, and especially the shape of the sea floor leading up to the coast. A broad, gradual sea bottom like that in the Gulf of Mexico leading up to New Orleans can allow water to build up more than a sea floor that drops abruptly, like that east of Florida.
It is difficult to determine the height of a storm surge until scientists can get out into ruined neighborhoods and measure the high water marks—which can vary along even a fairly short stretch of coast. As of today, estimates for Haiyan’s surge are between 15 and 20 feet where it first made landfall. Hurricane Sandy’s surge topped out at about 13 feet in New York City and northern New Jersey. Hurricane Katrina’s surge was 24 to 28 feet along the Louisiana Coast.
These monster storms often raise the notion that scientists should expand the Saffir-Simpson hurricane scale. A category 1 storm has winds of 74 to 95 mph, and the stages rise every 20 mph or so. But because a category 5 storm is rated at 157 mph or higher, it makes sense to some observers to create a new category 6 for storms like Haiyan that are so far above that speed.
Masters doesn’t see the benefit, however, and even sees a potential pitfall. Anything higher than category 5, he says, would not make warnings or evacuation orders any stronger or alter actions that emergency personnel would take. “It wouldn’t help as far as getting people to do the right thing,” he explains. “And if there were a category 6 storm, and it was downgraded to category 5, people might say, ‘Oh, it’s weakening.’ But category 5 is already catastrophic.”
Image: Courtesy NOAA