El Niño is the name for an irregular cyclical climate phenomenon in the Pacific Ocean that affects weather around the world. Named by fishermen who happened to first observe the phenomenon while sailing the coast of South America at Christmas. They noticed that the surface temperature of the ocean was much warmer than in typical years, they couldn't catch any fish, and it was rainier than usual. It wasn't until much later that El Niño could be explained as a global climate pattern. When warm waters were noticed near the coasts of Central America, North America, and South America, people endured cooler waters and drought Southeast Asia and Australia. The cyclical nature of these events are referred to as El Niño-Southern Oscillation, or ENSO (L'Heureux, 2014). Another way to think about ENSO is water sloshing back and forth in a bathtub. Warm waters build up on one side of the Pacific, then temporarily slosh east before winds push the surface waters west again. These El Niño events happen somewhat regularly, on average 5-7 years.
In normal conditions, we see warm waters in the tropical western Pacific (Southeast Asia and Australia) and cool waters in the eastern tropical Pacific (South, Central, and North America) as prevailing winds keep pushing surface waters west. The cool waters in the eastern Pacific upwell from the deep, bringing nutrients and supporting wildlife. An extreme version of these conditions is referred to as La Niña, where coastal areas in the eastern Pacific receive less rain due to less evaporation. This year (2020) is predicted to be a La Niña year, so prepare for less rain than usual. Keep an eye on NOAA's climate center for updates.