What do hurricane categories actually mean?

The Saffir-Simpson scale classifies hurricanes by maximum sustained wind speed: Category 1 from 74 to 95 miles per hour, Category 2 from 96 to 110, Category 3 from 111 to 129, Category 4 from 130 to 156, and Category 5 at 157 and above. Categories 3 and up are termed major hurricanes. The scale is useful for what it measures, since wind damage escalates sharply with speed, and it is the number that dominates public attention and evacuation decisions.

Its limits are the problem. The scale does not account for storm surge, the wall of ocean water pushed ashore, which is the leading cause of hurricane deaths and depends on the storm's size, forward speed, angle of approach, and coastal geography rather than on wind category alone. It does not account for rainfall, which produced most of the catastrophic damage from Harvey in 2017, a storm that stalled over Houston, and from Florence in 2018. And it does not account for the storm's physical size, so a large Category 2 can produce a far worse surge than a compact Category 4. Sandy in 2012 was barely a hurricane by wind at landfall and caused tens of billions in damage.

The National Hurricane Center has responded by issuing separate storm surge watches and warnings, with inundation maps showing expected water depth above ground, and by emphasizing that evacuation orders are based on surge zone rather than category. The practical guidance follows: know your evacuation zone, which is determined by elevation and surge exposure, and act on the order for your zone rather than on the category. People who ride out a Category 1 because it sounds minor and then drown in a surge are a documented and recurring pattern.