Tropical Cyclone Hazards

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Edexcel iGCSE > Hazardous Environments > Tropical Cyclone Hazards

Causes of Tropical Cyclones

Tropical cyclones, also known as tropical storms, arise from areas of low atmospheric pressure. They form over warm ocean waters—typically those with temperatures above 27°C—where the heat supports significant evaporation. These systems develop in the tropics, away from the Equator, where the Coriolis Force supports the storm’s rotation. To initiate a cyclone, the lower and upper layers of the atmosphere must have winds blowing in the same direction, which minimises vertical wind shear or the variation in wind speed and direction at different altitudes.

These storms are marked by heavy rainfall and extreme winds that can lead to devastating storm surges, coastal flooding, and inland hazards like river flooding and landslides. The severity of tropical cyclones can vary, with stronger systems causing more significant and widespread damage.

The impacts of different types of tropical storms are illustrated below:

Category	Features	Impact
1	Winds 119-153 km/h; storm surge generally 1.2-1.5 m above normal	Minor damage occurs to buildings, mainly limited to unsecured mobile homes. There can be some flooding on coastal roads and minor damage to piers.
3	Category 3: Winds 178-209 km/h; storm surge often 2.7-3.6 m above normal	Smaller houses and utility buildings may suffer structural harm, and mobile homes could be destroyed. Coastal flooding can obliterate small structures, with larger buildings incurring damage from debris. Residents in low-lying shoreline areas might need to evacuate.
5	Category 5: Winds greater than 252 km/h; storm surge typically greater than 5.5 m above normal	Many homes and industrial buildings may experience complete loss of roofs. Some smaller structures could be toppled or carried away by winds. Escape routes near the coast may become impassable due to rising water 3-5 hours before the tropical storm’s centre arrives. A significant evacuation could be necessary for residential zones within 8-16 km of the coast.

Summary

Tropical cyclones develop over oceans with temperatures exceeding 27°C, and require uniform wind directions across different altitudes to reduce vertical wind shear and form between the tropics away from the Equator, where the Coriolis effect initiates rotation.
They are marked by torrential rain and strong winds, leading to storm surges and coastal and inland flooding, with more powerful storms inflicting more significant and more extensive damage.
Category 1 storms, with winds of 119-153 km/h, typically cause minor structural damage, primarily to unsecured mobile homes, coastal road flooding and pier damage.
Severe Category 3 and 5 storms, with winds reaching 178-209 km/h and exceeding 252 km/h respectively, can lead to the destruction of buildings, total roof collapses, and may necessitate extensive evacuations due to substantial storm surges and compromised escape routes.