In parts across the worldhurricanes have hit.InU.S.A, 2017 Hurricane Harvey hit texas.Thenumber of major hurricanes which have occurred in 2017 are6.the scale that measures hurricanes is called the Saffir -Simpson scale.Acategory one hurricane has winds of 74 to 96 miles per hour.Acategory two hurricane has winds up 96 to 110 mph.Acategory three hurricane has winds up to 111 to 129 mph.Acategory for hurricanehas winds up to 130 to 146 mph.Acategory five storm has winds greater than 157 mph.Whatcauses hurricanes,though?Hurricanesdevelop from tropical storms.But, only some tropical storms change into hurricanes, which is based on how fast the storm’s wind speed is.Atropical 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.