“It’s highly unusual to have two highs on either side of a hurricane of equal strength.” The only other time Masters recalls that happening to a huge storm system was Hurricane Mitch in 1998, which struck Central America and killed an estimated 7,000 people in Honduras. ![]() “The systems have equal strength and are cancelling each other out,” leaving Harvey stranded, Masters says. is trying to push the storm in the opposite direction. is trying to push the storm in one direction, but a big high pressure system over the southwestern U.S. In Harvey’s case, a big high-pressure system over the southeastern U.S. Hurricanes are circular structures with winds that spiral counterclockwise, but they are steered by larger wind patterns in the greater atmosphere that push them in one direction. Why is Harvey so stuck in place over Texas? Hurricane Katrina, which destroyed New Orleans in 2005, also mushroomed to Category 4 in a similar fashion because it, too, passed over a hot eddy in the Gulf. The hotter the water, the more energy it drives into a storm. This spot of hot water was 1 to 2 degrees Fahrenheit warmer than the Gulf of Mexico around it, which itself was already 1 to 2 degrees F higher than average, reaching 85 or 86 degrees F in places. That is because it happened to pass over a region of extremely warm ocean water called an eddy. On Friday it rapidly ballooned from a Category 1 hurricane to Category 4. Last Wednesday night, August 23, Harvey was a tropical depression, but after just eight overnight hours it was forming a hurricane eye wall. ![]() Why did Hurricane Harvey so quickly explode from a Category 1 hurricane to Category 4? Masters also wrote a fascinating article on why the jet stream is getting weird. Masters is the co-founder of Weather Underground, a web site that meteorologists nationwide go to for their own inside information about severe weather. Scientific American wanted to learn why, and we asked meteorologist Jeff Masters for help. That is just one of the hurricane’s extremes the storm is off the charts by many measures. Experts say Harvey has been stuck longer in one place than any tropical storm in memory. "The rate at which that water has to be dealt with is different than it was 40 years ago.Hurricane Harvey is drowning southeastern Texas for the fourth day, putting a vast area under feet of water. That increases runoff and makes it difficult for the flat metropolitan area to drain. "As the suburbs have grown, pavement has spread," he says. ![]() Houston has been booming since the mid-2000s, and its ever-expanding suburbs have meant fewer natural barriers for heavy rainfall. Hoerling says the growth of the Houston metropolitan area may have a far larger influence on the storm's effects than climate change. Tropical storms Claudette in 1979 and Allison in 2001 also created enormous rainfall totals because of their slow-moving characters.Īnd the biggest contributor might be a different man-made factor Hoerling says that meandering storms appear to be a feature of the region. It lingered in the same region for days, dumping rainfall over Houston that is being measured in feet, not inches. The key feature that makes Harvey so devastating is that it stalled out over Texas. But as a first estimate, "it's probably not unreasonable."īut climate change isn't completely responsible for the devastation "It's early to know whether we can just put that knowledge into the experience over South Texas with Harvey," Hoerling says.
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