Geography
What is a hurricane?
Quick answer
A hurricane is a giant spinning storm that forms over warm ocean water, with strong winds and heavy rain. In other parts of the world it is called a typhoon or a cyclone.
In one sentence
A hurricane is a huge, rotating storm that grows over warm tropical oceans and brings very strong winds, heavy rain and high seas.
Explained
Hurricanes begin over warm ocean water, where sea water at around 26.5 degrees Celsius or more heats the air above it. Warm, moist air rises, and more air rushes in to replace it. Thanks to Earth's spin, the whole system starts to turn. Clouds build up in a giant spiral, and a low-pressure area forms at the centre.
The same type of storm has different names depending on where it forms:
- Hurricane: the Atlantic Ocean and north-east Pacific.
- Typhoon: the north-west Pacific, near Asia.
- Cyclone: the Indian Ocean and the south Pacific.
wind
cloud
wave
A hurricane has clear parts. In the middle is the eye, a calm area, sometimes with blue sky, about 30 to 60 kilometres across. Around the eye is the eyewall, a ring of towering clouds with the strongest winds and heaviest rain. Beyond that, long spiral bands of rain stretch outwards. In the northern hemisphere, hurricanes spin anticlockwise, and in the southern hemisphere clockwise.
To be called a hurricane, the winds must blow at 119 kilometres per hour (74 miles per hour) or more. The Saffir-Simpson scale rates them from category 1 to category 5, from the weakest to the strongest. The greatest danger often comes from the storm surge, a rise in sea level pushed onto the land by the wind, and from flooding by heavy rain.
When a hurricane moves over land or cold water, it loses its energy and fades. Forecasters track storms with satellites, planes and computer models, and issue warnings. Storms are given names from a list for each year, such as Dorian or Laura, to help people follow them. The Atlantic hurricane season runs from June to November.
If a warning is issued for your area, follow official advice, which may include going to a shelter. See weather for more on storms, climate for patterns across the year, and oceans for the sea that powers them.
Examples
| Name | Where | Season |
|---|---|---|
| Hurricane | Atlantic, north-east Pacific | June to November |
| Typhoon | north-west Pacific | mostly summer and autumn |
| Cyclone | Indian Ocean, south Pacific | about November to April in the south |
Common mistakes
- "Hurricanes and tornadoes are the same." Tornadoes are much smaller and form over land.
- "The eye means the storm is over." The back side of the eyewall is still ahead.
- "Only the wind is dangerous." Floods and storm surge cause much of the harm.
Quick quiz
Hurricanes
Check what you know with 4 quick questions.
Question 1 of 4
What do we call a hurricane in the north-west Pacific Ocean?
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