According to the British Broadcasting Corporation Weather Centre, tornadoes occur when warm and cool airstreams collide. A rotating area of low-pressure storm clouds form. Air within a low pressure front rises, creating a strong upward draught like a vacuum cleaner, and this draws in surrounding warm air from ground level, causing it to spin faster and faster. These strong air currents can create a vortex ? a spiralling funnel of wind ? that can reach speeds of 300mph. Where the funnel touches the ground, it creates a path of concentrated destruction, rarely more than 250m across.

Waterspouts are a fairly common meteorological phenomena, and are often referred to as tornadoes over the sea. There are, in fact, two types of waterspouts, tornadic and fair weather.

The former, generally the more dangerous of the two, actually forms as a tornado over the land and drifts out to sea. Fair weather waterspouts, which are by far the most common of the two varieties, are most likely to form over the open sea, or large lakes, in the late summer or autumn when the sea temperature is at its highest.

If, then, a cool mass of air moves over the warm sea, the air becomes very humid and unstable, and this sets up strong convection currents which may be sufficient for a water spout to develop.