Why do some years bring many more hurricanes than others?

Tropical cyclone formation depends on multiple ingredients lining up at once. Warm ocean water, moist air, and low vertical wind shear encourage storms to organize and intensify. El Niño often increases wind shear in the Atlantic and can reduce hurricane activity there, while La Niña often has the opposite effect. Because these climate factors vary from year to year, hurricane seasons can be dramatically different even in the same ocean basin.