Some says these have been happening.. yes, they are happening periodically, but probably only recently due to global warming in recent years..
There are pictures here: http://waves.marine.usf.edu/elnino_menu/elnino_menu_article.htm
Normal situation: trade winds blow from Eastern Pacific Ocean (South America) to Western Pacific Ocean, resulting in 0.5m higher sea level at Indonesia area. Water is thus warmer at Western Pacific Ocean (WPO) than colder Eastern Pacific Ocean (EPO) – 8 degrees Celsius. Colder area air has higher pressure than warmer air, so atmosphere/air/winds also change.
El Niño or La Niña: Situation where sustained sea surface temperatures anomalies is greater than 0.5 degrees Celsius.
El Niño: Westerly trade winds relax, thus less rain at WPO.
La Niña: Westerly trade winds increase, thus more rain/colder at WPO.
-> Something like that lah..