An eastward shift in where the tropical precipitation forms over the Pacific, known as the Southern Oscillation also happens.
El Niño is an anomalous warming of the Eastern Equatorial Pacific Ocean, typically covering much of the area from the South American coast to west of the dateline. An eastward shift in where the tropical precipitation forms over the Pacific, known as the Southern Oscillation also happens. The opposite is La Niña, when anomalously cold waters occur in the Eastern Equatorial Pacific Ocean and there is a westward shift of precipitation. Collectively, these are the phenomenon known as El Niño-Southern Oscillation (ENSO).