These are tropical storms with winds stronger than 75 miles per hour (120 km/h). They're called hurricanes when they form in the northern Atlantic Ocean and the northeastern or southern Pacific Ocean, typhoons when they form over the northwestern Pacific, and cyclones when they form over the Indian Ocean. These dangerous storms form when tropical winds gather moisture as they pass over water that is at least 80°F (27°C). The winds of a hurricane rotate around an eye, or center of the storm. Hurricanes are strongest when they're over water, but they can remain fierce after reaching land, which is where they do the most damage. They are measured in categories, ranging from Category 1, which have winds from 74 to 95 mph (119 to 153 km/h) to Category 5, which have winds greater than 155 mph (250 km/h).