Hurricane Categories Don’t Capture How Dangerous Florence Is

The Saffir-Simpson Hurricane Wind Scale only measures wind speed and nothing else.

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Sep 14 2018, 5:59pm

Image: NASA

By the time Hurricane Florence made landfall this morning, it had been downgraded from a Category 4 storm to a Category 1. Although this is good news, the storm is still dangerous and shouldn’t make you complacent. A Category 1 storm can still be devastating, because the scale we use to categorize storms only takes into account one factor—wind speed—and when it comes to hurricanes there are many other factors to worry about.

The categories we give to hurricanes are based on the Saffir-Simpson Hurricane Wind Scale, which was developed in the 1970s as a way to simply communicate a hurricane’s intensity. Each category (1-5) is determined exclusively by wind speed—a category 3 hurricane, for example, has wind speeds between 111 and 129 miles per hour.

Wind speed certainly contributes to how destructive a storm will be, but it’s not the only factor. Rainfall, storm surge (where the sea level rises due to the pressure of the storm), flooding, and the physical size of the storm all contribute to what kind of impact it will have on land. And according to the American Meteorological Society, storm surge accounts for almost half of all directly storm-related deaths in the US, compared to wind, which accounts for 8 percent.

While having higher wind speeds would certainly have made Hurricane Florence worse, the other factors are still severe. Forecasts from the National Hurricane Center predict that in the hardest hit areas “life-threatening” storm surge could reach heights of 11 feet, rainfall may total up to 40 inches, and “catastrophic” flooding is likely to occur.

The Saffir-Simpson is a really handy rule of thumb and often the best way to quickly warn the public about the severity of a storm, but it’s important not to let a lower category, or a downgrade to tropical storm, lull you into complacency.

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