Hurricane activity in the Atlantic basin goes through cycles. The last period of intense activity was in the 1950s and 1960s. With the exception of the El Nino years of 1997 and 2002, the Atlantic hurricane seasons have been busier than normal since 1995. There have already been 13 named storms and three major landfall hurricanes this year.
If the forecasts are right, there will be 22 tropical storms - 11 of which will become hurricanes, with seven becoming major hurricanes - by the end of the season in November.
Hurricanes are classed one to five on the Saffir-Simpson scale. Category one (minimal) has wind speeds of 74-95mph. Category five (catastrophic), known as a super hurricane, has speeds of 155mph or more.
Hurricane Katrina was category one when it hit Florida, grew to category five over the Gulf of Mexico and eased to category four before hitting Louisiana.