Hurricanes are violent storms that can bring devastation to coastal areas, threatening lives, homes and businesses.
Hurricanes develop from thunderstorms, fuelled by warm, moist air as they cross sub-tropical waters.
Warm air rises into the storm.
Air swirls in to fill the low pressure in the storm, sucking air in and upwards, reinforcing the low pressure.
The storm rotates due to the spin of the earth and energy from the warm ocean increases wind speeds as it builds.
When winds reach 119km/h (74mph), it is known as a hurricane - in the Atlantic and Eastern Pacific - or a typhoon in the Western Pacific.
The eye of the storm
The central eye of calmer weather is surrounded by a wall of rainstorms.
This eyewall has the fastest winds below it and violent currents of air rising through it.
A mound of water piles up below the eye which is unleashed as the storm reaches land.
These storm surges can cause more damage from flooding than the winds.
The size of hurricanes is mainly measured by the Saffir-Simpson scale - other scales are used in Asia Pacific and Australia.
Winds 119 to 153km/h
Some minor flooding, little structural damage.
Storm surge +1.2m to 1.5m
Winds 154 to 177km/h
Roofs and trees could be damaged.
Storm surge +1.8m to 2.4m
Winds 178 to 208km/h
Houses suffer damage, severe flooding
Storm surge +2.7m to 3.7m
Winds 209 to 251km/h
Some roofs destroyed and major structural damage to houses.
Storm surge +4m to 5.5m
Serious damage to buildings, severe flooding further inland.
Storm surge +5.5m