The National Hurricane Center determines what a storm's category, between 1 and 5, based on the Saffir-Simpson Hurricane Wind Scale, which estimates potential property damage based on the storm's ...

When it comes to hurricanes, one of the biggest questions is what category it will be. Hurricanes are categorized using the Saffir-Simpson scale, which is based on sustained wind speed.

So in other words, a Category 3 would be three times as much rainfall as you would expect to see in an area in a five-year period. Basically, long story short, there's many ideas how to do this.