El Niño-Southern Oscillation, also known as ‘ENSO’ for short, means ‘The Little Boy’ or ‘Christ Child’ in Spanish. It is a large scale ocean-atmosphere climate interaction that originates in the Pacific ocean but spreads across the world. The occurrence of El Niño can considerably influence weather patterns, ocean conditions, and aquatic fisheries across large portions of the world for a prolonged period of time. El Niño is linked to a period of warming in the central and east-central Equatorial Pacific region. El Niño and La Niña typically last from 9 – 12 months; however, each occurrence can vary with prolonged periods lasting as long as a few years. The frequency of El Niño is also irregular, with events occurring on average every 2 – 7 years. El Niño occurs more frequently than La Niña.
Over the North American continent, consequences of El Niño develop during the winter season. Such impacts include above average temperatures over Western and Central Canada, and Western and Northern United States. The U.S. Gulf Coast also experiences wetter than average conditions while in contrast regions in the Ohio Valley and Pacific Northwest experience drier than average conditions. Weather and ocean temperatures are interlinked; where there are warm oceans, more clouds form, creating more rain fall in that region of the world.  Near the equator, the surface of the Pacific Ocean is quite warm due to the angle of solar energy approaching the ocean surface. Strong winds typically push warm waters from South America and drive them toward Indonesia. This causes cooler water underneath to rise up toward the surface of the ocean near South America. Now during an El Niño event, there are more rain clouds produced over this part of the warm Pacific waters. These clouds travel inland and cause more rain than on average in Southern and Central America and in the United States. Although this is not the case in other parts of the globe where regions can experience severe drought.
El Niño causes predictable disruptions in temperature, precipitation, and winds. These changes impact large-scale air movements in the tropical regions, which trigger a cascade of global side effects. El Niño can lead to extreme weather patterns such as strong forest fires due to drought that have been correlated during El Niño events. Northeastern Brazil for example typically experiences extreme droughts but in contrast southern Brazil experiences large amounts of rainfall. A warming of the ocean surface, or also known as above-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean occurs during ENSO. Over Indonesia, rainfall is reduced while rainfall increases over the tropical Pacific Ocean. El Niño and La Niña have their strongest impact on global climate during the Northern Hemisphere winter & early spring. However, parts of the tropics and Southern Hemisphere sub-tropics feel the effects of ENSO during Northern Hemisphere summer months of June to August.
Below is a video to help understand what El Niño is with visual aid: