How Hurricanes Are Categorized on an Imperfect Scale

As it approached Louisiana’s coastline, Tropical Storm Francine was threatening to grow into a Category 1 hurricane. That only tells part of Francine’s story and measures just a fraction of its threats. The category is part of the Saffir-Simpson Hurricane Wind Scale, which is cited routinely (if rarely by its full name) during the Atlantic hurricane season. The scale captures only wind speeds, which are just part of what can make a hurricane dangerous to people and property. Rain and storm surges can be a hurricane’s most damaging elements.

It’s a five-step scale created in the 1970s by Herb Saffir, an engineer, and Bob Simpson, a meteorologist, to categorize a hurricane’s power, from Category 1 (sustained winds of at least 74 miles per hour, or 119 kilometers per hour) to Category 5 (157 mph and greater). Anything above a Category 3, which is reached when a storm’s winds hit 111 mph, is considered a major hurricane. The scale is used primarily in the Western Hemisphere, where the US National Hurricane Center has responsibility for forecasting.