El Nino is an unusual warming of surface ocean waters in the eastern tropical Pacific. It is the pattern of reversing surface air pressure between the eastern and western tropical Pacific. When the surface pressure is high in the eastern tropical Pacific it is low in the western tropical Pacific.
The ocean warming and pressure reversals happen at the same time. The name came from South American fisherman. El Nino is Spanish for "The Christ Child". This weather pattern comes about the time of the celebration of the birth of the Christ Child Christmas.
climate (n.) – weather patterns for a particular area
pattern (n.) – the regular way something happens for several years
pressure (n.) – weather: a condition of air that affects Earth's atmosphere; a barometer measures air pressure.
reversing (adj.) – changing in direction; reversals (n.)
surface (n.) – the top layer of an area of water or land
tropical (adj.) – coming from or existing in the hottest parts of the world near the equator, between 23.5° N and 23.5° S latitude