Lousiana may have been spared the widely expected large scale devastation at the hands of Hurricane Gustav, but there is plenty of other trouble in store.

As the residents of New Orleans think about returning to their homes, populations along the coast of Georgia and South Carolina are ready to evacuate theirs. Hurricane Hannah has been churning slowly through the Atlantic for some time, and struck the Bahamas on Tuesday 2 September. It is expected to gather speed and power before launching an assault on the East Coast of the US, possibly on Friday.

Hot on the heels of Hannah will come Tropical Storm Ike, expected to become a hurricane before striking the Bahamas. And behind that is Tropical Depression 10, out in the open Atlantic.

This is now the peak of the hurricane season, and most storms develop along “Hurricane Alley”, which stretches across the tropical Atlantic seas.

West Africa is the launch pad for most of the trouble, starting off as thunderstorms that roll off the coast on to the sea. If these thunderstorms form a cluster they can get blown westwards on the trade winds, and are known as tropical waves. As these clusters sail over the warm seas, they feed off the warm waters, grow stronger and can start to rotate into a tropical depression, which is then given a number. The storms spiral into a familiar shape and gather more strength, turn into tropical storms and are given a name.

Eventually these can develop into hurricanes. However, hurricanes are actually quite unusual — only about one out of ten tropical waves develops into a hurricane.