Science

Why we can’t predict how destructive a hurricane season will be

Hurricane season begins today in the Atlantic, and the National Oceanic and Atmospheric Administration (NOAA) is predicting that there will be up to nine hurricanes, including one to four major storms with winds blowing at 111 mph (about 178 km/h) and up. How many of these hurricanes will make landfall, though? This far in advance, it’s impossible to say. The only thing to do is to prepare the best you can for a hurricane strike — whether or not it’ll happen.

“Whether we predict five to nine hurricanes and all of a sudden you wind up with 10, that’s not important at this stage,” says Gerry Bell, the lead hurricane season forecaster with NOAA’s Climate Prediction Center. “Even though we can’t predict exactly who’s going to get struck, it’s still very important that people know that hurricane season is starting.”

Forecasting how many hurricanes will form from June to the end of November — the length of the Atlantic hurricane season — is incredibly complicated. Researchers at NOAA, as well as other institutions like Colorado State University, look at a variety of factors, like ocean temperatures, pressure in the atmosphere, wind patterns, and historical data.

“What you do is you look for large-scale climate conditions that tend to predispose a season one way or the other,” says Phil Klotzbach, a research scientist at Colorado State University’s Department of Atmospheric Science, who comes up with CSU’s seasonal outlooks. All this information is then fed into supercomputers that spit out predictions and tell forecasters whether the hurricane season will be above, near, or below average. An average season has 12 named storms, including six hurricanes, of which three are Category 3, 4, or 5, according to NOAA.

The most important and the trickiest climate condition to keep an eye on is El Niño, a recurring weather pattern that brings warm waters to the tropical Pacific Ocean. When there’s an El Niño, you don’t get as many hurricanes in the Atlantic Ocean. That’s because El Niño tends to unleash strong, high winds that tear the hurricanes apart, making it hard for them to form, Klotzbach says.

The problem is that in the spring, when CSU and NOAA publish their first hurricane seasonal outlooks, it’s really hard to predict how El Niño is going to behave later in the year. That makes it tricky to guess how many hurricanes will form. Right now, climate models are split: half of them say that we’re going to have a mild El Niño, and the half say there’ll be no El Niño at all, says Sonya Miller, the associate director of Penn State’s Earth System Science Center. At this moment, the NOAA forecasts give a wide range in the number of storms that might develop: from 10 to 16, with five to nine hurricanes.

Last year, climate models indicated that an El Niño was going to develop, and so the early forecasts called for a near-average hurricane season, Klotzbach says. “Obviously, last year was anything but normal,” he says. There were 17 named storms, including 10 hurricanes and six major hurricanes, of which three made landfall in the US. The storms cost the US about $265 billion in damages, according to NOAA. Unlike what the models had predicted, El Niño did not develop. Plus, there were weaker-than-normal winds blowing across the surface of the ocean, which caused the Atlantic to warm up very quickly, especially in June and July. And hurricanes get their fuel from hot waters.

“It really, really ramped up,” Klotzbach says. “And so people started to realize, ‘Oh man, it’s going to be a lot more active than they had originally thought.’”

The seasonal forecasts that come out in the spring are usually updated during the summer, as peak hurricane season in August gets closer. Those forecasts are more precise, but they still can’t tell where the hurricanes are going to strike. That can only be calculated for individual storms once they’ve formed: it depends on too many variables, like when the hurricane developed, how strong its winds are, where it’s going, and the atmospheric pressure, which is all information that’s collected by satellites, buoys, radars, as well as reconnaissance aircraft.

“It’s pretty much impossible to say at this point how many are going to make landfall,” says Kevin Trenberth, a distinguished senior scientist at the National Center for Atmospheric Research. “The track is something that’s very much depending on the weather. It’s got a large crapshoot element to it.”

So, why make seasonal forecasts at all? “It’s the same reason why your weatherman does a seven-day forecast even though the forecast is going to be much better for tomorrow,” Klotzbach says. “People want to know.” And “people” aren’t just those living on the coast. Over 80 million people in the continental US can be impacted by hurricane flooding and wind, according to Bell. Government officials use seasonal forecasts to know what to expect and start preparing for hurricanes, he says.

Klotzbach, however, pleads caution: it doesn’t matter how many hurricanes are forecasted; it takes only one storm to put people in danger. In 1992, for instance, there was only one major hurricane, but that Category 5 storm — Hurricane Andrew — ravaged South Florida, causing the death of 65 people and destroying over 25,000 homes. In comparison, there were 12 hurricanes in 2010 — twice as many as an average season — but none hit the US, Klotzbach says.

So, at this moment, the only thing to do is get ready. People living in the Caribbean, the Gulf of Mexico, and the eastern coast of the US should check their insurance coverage and come up with an evacuation plan, as well as ways to get in touch with their family members after disaster hits, according to Daniel Kaniewski, deputy administrator for Protection and National Preparedness at the Federal Emergency Management Agency. It’s also a good idea to prepare an emergency kit.

Once storms form, it’s also important to check with the National Hurricane Center for updates. In the meantime, these seasonal outlooks are all we’ve got. And although they’re limited, they’re still pretty cool. “I find it a fascinating exercise, trying to understand basically what makes mother nature tick,” Klotzbach says. “I just find it challenging.”

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