Aerial photograph of tropical cyclone

What are hurricanes?

Tropical cyclones start as clusters of clouds over tropical oceans which amalgamate and rotate to form a tropical depression. When the sustained wind speeds around the tropical depression reach 39 mph it becomes a tropical storm and is assigned a name. Different naming conventions are used globally, but all result from the same processes. When wind speeds reach 74 mph, the tropical cyclone is referred to as a hurricane, typhoon or simply a cyclone depending upon where it is on the globe. By this stage they can be 300 to 500 miles across and up to five to six miles high.

If the tropical cyclone travels polewards towards the mid-latitudes, it can make a transition into an extratropical or post-tropical storm.

Hurricanes cannot form at the latitudes of the UK as they require much higher sea surface temperatures to develop than exist close to the UK. However, the UK is sometimes affected by extratropical storms as they move to higher latitudes, such as ex-Hurricane Ophelia in 2017. Occasionally, intense mid-latitude depressions can produce near hurricane strength winds. The most widely publicised such depression occurred on 16 October 1987, known as The Great Storm.