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.
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.
"Everybody has a plan until they get punched in the face. Well, we're about to get punched in the face."
"Urgent warning about the rapid rise of water on the SW FL coast with the passage of #Irma's eye. MOVE AWAY FROM THE WATER!"
The size of hurricanes is mainly measured by the Saffir-Simpson scale - other scales are used in Asia Pacific and Australia.