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A hurricane is a powerful storm that forms over warm tropical or subtropical ocean water.
It is a kind of tropical cyclone, a rotating system of low pressure organized around thunderstorms.
Scientists classify these storms by their maximum sustained wind speed.
A system with winds below 39 miles per hour is a tropical depression.
When winds reach 39 miles per hour, it becomes a tropical storm.
At 74 miles per hour, the storm is officially called a hurricane.
The Saffir-Simpson scale then ranks hurricanes from category 1 to category 5.
A higher category means a greater potential for damage to property.
Hurricanes form mainly in the Atlantic basin, which includes the Atlantic Ocean and nearby seas.
They also occur in the eastern North Pacific and, less often, in the central North Pacific.
The Atlantic hurricane season officially runs from the first of June to the end of November.
Storms have sometimes formed outside those dates, so the season is only a guide.
A national hurricane center predicts and tracks these systems to warn people in danger.
Each storm receives a name from a rotating list kept by the World Meteorological Organization.
NOAA studies hurricanes to protect people, property and natural resources.
Preparedness before a storm arrives is one of the most important ways to stay safe.