Relation between Saffir–Simpson Hurricane Scale Wind Speeds and Peak 3-s Gust Speeds over Open Terrain

Abstract

The Saffir–Simpson scale for categorizing hurricane intensity and damage potential is increasingly being used by hurricane forecasters and emergency managers. The hurricane intensity categories are associated in the scale with 1-min wind speeds. For structural engineering purposes the ASCE 7 Standard defines these 1-min speeds as speeds at 10m over open water. This technical note provides estimates of the ratio of peak 3-s wind speeds at 10m over open-terrain exposure—the speeds used in the ASCE 7 wind map—to 1-min speeds at 10m above open water. Based on the ASCE 7 power-law model, the estimated ratio is 1.03. Based on the logarithmic law model, depending upon assumptions pertaining to the surface roughness for flow over open water, and upon the estimation method, the ratio varies from 1.03 to 1.12.