These three maps based on satellite data show sea levels in the Pacific Ocean during developing El Niño events in early October of 1997, 2015, and 2023. Higher-than-average ocean heights are shown in red and white, while lower-than-average heights are blue and purple. The two earlier maps represent the two extreme El Niño events from the past 30 years - the first from 1997 to 1998 and the second from 2015 to 2016. Both caused shifts in global air and ocean temperatures, atmospheric wind and rainfall patterns, and sea level. El Niños are characterized by higher-than-normal sea levels and warmer-than-average ocean temperatures along the equatorial Pacific. Water expands as it warms, so sea levels tend to be higher in places with warmer water. These temperature and sea level conditions can then propagate poleward along the western coasts of the Americas. El Niños can bring wetter conditions to the U.S. Southwest and drought to regions in the western Pacific, including Indonesia. Not all E