According to the National Oceanic and Atmospheric Administration, El Niño and La Niña are the warm and cool phases of a climate pattern across the tropical Pacific. The patterns shift back and forth every two to seven years and vary in strength, causing changes in ocean temperature that lead to droughts, floods and heat waves in different parts of the world. 

El Niño has the strongest influence on U.S. winter weather, but in the summer, it reduces hurricane activity in the Caribbean and Atlantic. The pattern also makes it wetter across the southern third to half of the country, including California, while regions in the Pacific Northwest and parts of the Ohio Valley are dry and warm. Outside the U.S., El Niño brings drier weather to Australia, Indonesia, India, and parts of southern Africa and northern South America, and wetter conditions in Southeast Argentina, parts of Chile and Northeast Africa.

This year’s El Niño formed earlier than usual, increasing the possibility of a strong effect on the weather, which when combined with human-caused warming, could result in record high global temperatures. Experts also say it is possible that record hot Atlantic Ocean water may counteract El Niño’s usual suppression of hurricanes this year.