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Hurricane winds bend tall palm trees. Hurricanes are tropical cyclones: massive spinning storms with strong winds (120 km/h or 75 mph and above) that form over the ocean in tropical areas. Hurricanes are known as tropical cyclones in the Indian Ocean or typhoons in the Pacific; strictly speaking, only in the Atlantic Ocean are they called hurricanes. They are common in summer months when the surface water temperature climbs above 27°C (80°F). Once formed, hurricanes drift westwards and can be very destructive. A large one may measure more than 2000 kilometres (about 1250 miles) across and rage for two or three weeks.

A cross-section through a hurricane showing the patterns of airflow inside it

How hurricanes occur

A satellite photo of a hurricane over FloridaHurricanes begin as warm, moist air is heated by the Sun and rises high into the atmosphere over the tropical Atlantic, Indian and Pacific oceans. The rising air sucks in more air, which begins to swirl around in a spiral. The moisture in the rising air condenses into clouds. Quickly the hurricane balloons in size and the swirling winds reach 250 km/h (150 mph). The spirals of deep cumulonimbus clouds unleash massive downpours, bringing up to half a year’s average rainfall in a few hours.
The hurricane moves along quite slowly, around 25 km/h (15 mph), as warmed air rises and swirls most powerfully near its centre. Most spills out at the top and is flung to the edges where it sinks. A small portion drifts down at the centre or “eye” of the storm. This is usually 25–40 kilometres (15–25 miles) across and, amazingly, it is calm with light
winds and clear skies.

Hurricane activity usually peaks in late summer, when the difference between air temperatures and sea temperatures is at its greatest.

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