The cause: water, warmth and whirling wind

The warm air rises while cooler, drier air descends to replace it. This process becomes faster and faster as the storm builds and a core of low pressure at the centre starts to drive the storm forward.

As it moves across the ocean it sucks more warm air in causing it to pick up speed, although it can take hours or even days to build into a full hurricane.

When the hurricane – or typhoons or cyclones as they are known in other parts of the world – is fully formed it consists of an area of low pressure and calm winds at centre and ferocious winds and heavy rain whipping around the outside.

Their power is measured in categories, from one to five. Irene was Category One – until it was lowered to a tropical storm.

Hurricane Katrina, in 2005, was a Category Four, while those with sustained wind speeds of more than 155mph are Category Five, and are mercifully rare.

Category One storms generally cause flooding and some damage to buildings and bridges.

Categories Four and Five cause mayhem inland, with loss of lives and homes, huge amounts of flooding and large pieces of land destroyed. Most of the damage done to low-lying areas is by the hurricanes’ “storm surge” – water being blown onshore by the high winds. Storm surges damage the ground floors of buildings and in extreme circumstances rip out their foundations, causing homes to wash away in the flooding.

When hurricanes start to die out they almost always travel poleward, transporting excess heat out of the tropics toward higher latitudes.

They gradually die as they move over cooler waters, which do not have the heat necessary to keep them going.

If the hurricane crosses to land, its heat source is removed entirely. Without heat to power it the hurricane can die out rapidly, particularly if the terrain is uneven, with cities or mountains.