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
ONEabove 98074 to 85Minimal
TWO979 to 96586 to 110Moderate
THREE964 to 945111 to 130Extensive
FOUR944 to 920131 to 155Extreme
FIVEbelow 920more than 155Catastrophic


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