As Tropical Storm Barry gathers strength on its way to a violent clash with the Louisiana coast, officials are rightly evacuating some residents, while advising others to shelter in place and have emergency plans in case the worst should happen. Barry is indeed a major threat — but the way we measure hurricanes may not be adequately driving home this storm’s dangers, renewing calls for alternatives.
The classic way to measure a hurricane’s strength is the Saffir-Simpson hurricane wind scale, which rates them on a 1-5 scale based on their sustained winds speeds. A Category 1 hurricane has sustained winds of at least 74 miles per hour, while a Category 5 has 157 mile-per-hour winds or faster.
But wind speed isn’t the only threat a hurricane or other tropical storm can bring — and sometimes it’s not even the primary danger. Storm surge, flooding and other hazards can be just as dangerous as high winds, if not more so. (Of course, there are connections between a hurricane’s wind speeds and how much flooding it can cause, especially along a coastline.) Indeed, the National Weather Service (NWS) is warning that Barry will bring 10-20 inches of rain (and possibly more in some areas), creating “widespread/life-threatening flash flooding and moderate to major river flooding,” in part due to how slowly it’s moving.
Furthermore, hurricanes sometimes lose strength as they make their way to land. Hurricane Florence, for instance, was a Category 4 hurricane before being downgraded to a Category 1 as it struck North Carolina last year. That kind of “demotion” can lull people in a storm’s path into a false sense of security, some experts say, because the downgrade makes it seem like a storm won’t be as bad. But even low-category hurricanes, or storms no longer strong enough to be considered a hurricane, can be dangerous. Sandy, for instance, was considered not a hurricane but a “post-tropical cyclone” when it struck the Northeast U.S. in 2012, causing about $65 billion in damage in the U.S.
Meteorologists and other experts have long debated whether an alternative to the Saffir-Simpson scale might help better communicate the risks of each major storm, potentially saving lives in the process. Earlier this year, AccuWeather did exactly that, introducing its “RealImpact Scale for Hurricanes.” Like the Saffir-Simpson scale, it rates storms on a numeric scale. But in addition to wind speed, it factors in estimates like flooding rain, storm surge, and even economic impact. It also includes a “less than 1” category for storms that fall short of a category 1, but pose risks nonetheless.
“It’s concerned me for 20-25 years, and we’ve worked for the last five or six to come up with a scale that does not confuse, but educates the public and helps them prepare for the magnitude of a storm and what the damage will be and where the threats come from,” AccuWeather Founder and CEO Dr. Joel Myers tells TIME. He says Barry’s biggest biggest risks are heavy rain and flooding, and his company estimates the storm will do $8-10 billion in damage, making it a two on the RealImpact Scale, while it’s currently a zero on the Saffir-Simpson scale.
Of course, a new scale is not the only way to communicate a storm’s dangers. Some organizations, the NWS included, have been more actively communicating a storm’s potential risks to life and property in ways that go beyond a numeric designation. But simple categories remain an effective way to concisely communicate a storm’s potential threat, so long as those categories take all dangers into account.
“Nothing’s perfect, but we think it’s certainly helped the conversation, and gives people more of an idea about how serious a particular storm is,” says Dr. Myers of the new AccuWeather scale. “It’s quite possible the storm will come ashore with winds under hurricane force, so it’ll be a zero on the Saffir-Simpson scale. But clearly in terms of its impact on the United States, in that whole area, it’s going to be far from a zero.”