A cyclone storm is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and squalls. Depending on its location and strength, a cyclone storm is referred to by different names, including hurricane, typhoon, tropical storm, cyclonic storm, tropical depression, or simply cyclone. The difference in names depends on the location of the storm. For example, in the Atlantic and the northeastern Pacific oceans, a tropical cyclone is generally referred to as a hurricane, while in the Indian and south Pacific oceans it is called a cyclone, and in the northwestern Pacific it is called a typhoon. The weakest tropical cyclones are called tropical depressions, and if a depression intensifies such that its maximum sustained winds reach 39 miles per hour, the tropical cyclone becomes a tropical storm. Once a tropical cyclone reaches maximum sustained winds of 74 miles per hour or higher, it is then classified as a hurricane, typhoon, or tropical cyclone, depending upon where the storm originates in the world.