Here is a simple explanation. El Niño is a climate pattern that involves the surface of the ocean and the atmosphere in the Pacific Ocean. Warm water along the equator, off the coast of South America, displaced colder water usually found in the Humboldt Current (Sometimes spelt as  Humbolt) , which is farther north.

The Humboldt Current carries plankton-rich, cold, Antarctic waters that are responsible for both the weather and the productivity of the Peruvian coast. The 13-17C (55-63F) waters, flowing from the southwest, carry huge quantities of plankton which provide a solid base for a diverse food chain of enormous biomass. Winds carry the surface waters away from the coast, resulting in the exposure of the colder subsurface waters. This upwelling, although present throughout the coast of Peru, occurs intensively at four sites, one of which is the Paracas Peninsula.

On the contrary, periodic shifts in the regional wind patterns known as El Niño can cause major changes in weather and biological conditions, involving the occurrence of warm water, excessive rainfall, floods, erosion, mudslides, and depletion or emigration of many species of fish and seabirds.

Usually, though not always, El Niño brings more rain and higher temperatures. Also, warm ocean currents come farther north and all kinds of tropical fish can be caught in the waters far north along the United States West Coast.

Recent years in which El Niño events have occurred are 1951, 1953, 1957-1958, 1965, 1969, 1972-1973, 1976, 1982-1983, 1986-1987, 1991-1992, 1994 and 1997. The high sea surface temperatures and the magnitude of the westerly wind anomalies over the Pacific are very high. These conditions suggest that the strength of 1997 El Niño event could equal or surpass that in 1982-1983, making it the strongest El Niño this century.

In 1982-1983, The El Niño of 1982-83 was responsible for the loss of nearly 2,000 lives and displacement of hundreds of thousands from their homes. The losses were caused by droughts and fires in Australia, Southern Africa, Central America, Indonesia, the Philippines, South America and India. There were floods in the USA, Gulf of Mexico, Peru, Ecuador, Bolivia and Cuba. More hurricanes than usual affected  Hawaii and Tahiti.

El Niño may also bring warmer than normal winter temperatures to the eastern part of the United States.