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The term "hurricane" is referred to a tropical cyclone occurring in the north Atlantic Ocean and along the western Pacific coasts of North America and affecting its coastal regions and islands and those of central America. The term "Typhoons", instead, indicates the same natural phenomenon, but when it occurs in the north-western Pacific Ocean and frequently hitting the coastal regions of China, Indochina, Philippines, Indonesia and Japan.

So, describing the different parts of a hurricane or of a typhoon is the same and they are defined "tropical cyclones" when there's not a frontal structure and its centre is warmer than its exterior "warm-core" and when wind speeds are constantly higher than 74 mph (118 Km/h).

A hurricane is formed in a deep pressure area on a tropical sea or ocean, between 5 and 20 degrees north and south of the equator, due to the Coriolis effect. The diameter of this low pressure area is not higher than 1000 Km and here, the intense evaporation of water vapour from the warm tropical waters of the ocean (above 27 C or 80 F) frequently forms thunderstorm clouds.

These stormy clouds raise upward with a convective motion that sucks further air and clouds from the surrounding areas. This motion can easily become swirling and form a roughly vertical eddy to which new air masses and clouds add further rotational energy, so, increasing its speed.

The clouds in the eddy move fast toward the upper layers of the troposphere where they cool down and move downward, while going to the exterior, respect to the centre. This causes intense rains around the hurricane centre and it pushes new hot air and vapour toward it.

- The eye.

The vortex of a hurricane leaves in its inside a low-pressure circular area, the "eye" where the air is relatively cleaner (so that, sometimes, it's possible to see the clear sky and the stars from the bottom of the eye) and relatively warm; here, rains and winds can be scarce or nearly absent. The diameter of the eye is variable with the dimensions of the hurricane, from 3 to 370 Km of diameter, approximately. Here, the pressure can drop down to 920 millibars or less, as it happens in the largest hurricanes, able to create the minimum low pressure zones of the world.

- The storm surge.

This low pressure central area attracts upward the water of the ocean forming the so-called "storm surge", a dome of water that floods the coastal and plain areas with waves from 1 m, in the category 1 hurricanes, to more than 6 metres in the

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