In parts across the world hurricanes have hit. In U.S.A, 2017 Hurricane Harvey hit Texas. The number of major hurricanes which have occurred in 2017 are 6. The scale that measures hurricanes is called the Saffir -Simpson scale. A category one hurricane has winds of 74 to 96 miles per hour. A category two hurricane has winds up 96 to 110 mph. A category three hurricane has winds up to 111 to 129 mph. A category for hurricane has winds up to 130 to 146 mph. A category five storm has winds greater than 157 mph.What causes hurricanes,though ?Hurricanes develop from tropical storms. But, only some tropical storms change into hurricanes, which is based on how fast the storm’s wind speed is. A tropical storm has a wind speed of up to 73 mph, but winds greater than 74 mph are classified as hurricanes. Hurricanes form over warm water so when a hurricane moves north it encounters land and it gets weaker.