“The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based on a hurricane’s sustained wind speed,” according to the National Hurricane Center. It is designed to estimate potential property damage based on the severity of the wind.
Hurricane Florence is a Category 4 storm. Here is the NHC’s definition of the effects of a Category 4:
“Winds (1-min sustained winds in mph): 130-156 mph
Summary: Catastrophic damage will occur.