Saffir-Simpson Scale

A tropical disturbance is any persistent area of thunderstorms that forecasters can track for several days in satellite pictures. When such a system develops a closed cyclonic circulation (south wind on the east side, east wind on the north, north wind on the west and, hardest to find, west winds south of the center) it becomes a depression and is numbered. When the maximum winds reach 35 kt, often with pressures still above 1000 mb, it becomes a tropical storm and receives a name. When it reaches 65 kt (74 mph) it is a hurricane. Hurricanes are classified by intensity into five categories:

Saffir-Simpson Scale
Category Pressure (hPa) Wind (mph) Damage
ONE above 980 74 to 85Minimal
TWO 979 to 965 86 to 110 Moderate
THREE 964 to 945 111 to 130 Extensive
FOUR 944 to 920 131 to 155 Extreme
FIVE below 920 more than 155 Catastrophic


Simpson, R. H., 1974: The hurricane disaster--potential scale.Weatherwise, 27, 169. back to main page