Measuring tropical cyclones
In order to categorise tropical cyclones around the world, the Saffir-Simpson Hurricane Wind Scale is used defining events by their wind speed and impacts.
Although developed in the USA, tropical cyclones around the world are measured by the Saffir-Simpson Hurricane Wind Scale which originated from 1971 with Herbert Saffir, a civil engineer and Bob Simpson of the US National Hurricane Center.
The Saffir-Simpson Hurricane Wind Scale consists of a five point scale of hurricane intensity and starts at 74 mph. Tropical cyclones with wind speeds up to 38mph are classified as tropical depressions and those with wind speeds from 39 - 73 mph are classified as tropical storms.
Saffir-Simpson Hurricane Wind Scale
Wind (mph): 74 - 95
Damage: Minimal - No significant structural damage, can uproot trees and cause some flooding in coastal areas.
Wind (mph): 96 - 110
Moderate - No major destruction to buildings, can uproot trees and signs. Coastal flooding can occur. Secondary effects can include the shortage of water and electricity.
Wind (mph): 111 - 129
Extensive - Structural damage to small buildings and serious coastal flooding to those on low lying land. Evacuation may be needed.
Wind (mph): 130-156
Extreme - All signs and trees blown down with extensive damage to roofs. Flat land inland may become flooded. Evacuation probable.
Wind (mph): greater than 156
Catastrophic - Buildings destroyed with small buildings being overturned. All trees and signs blown down. Evacuation of up to 10 miles inland
Other phenomena, which can be just as damaging as the wind, frequently accompany tropical cyclones These can include:
- High seas - large waves of up to 15 metres high are caused by the strong winds and are hazardous to shipping
- Storm surge - a surge of water of up to several metres can cause extensive flooding and damage in coastal regions
- Heavy rain - the tropical cyclone can pick up two billion tons of moisture per day and release it as rain. This can lead to extensive flooding - often well inland from where the tropical cyclone hit the coast
- Tornadoes - tropical cyclones sometimes spawn many tornadoes as they hit land which can cause small areas of extreme wind damage