Causes:
http://www.usatoday.com/weather/tg/wetnino/wetnino.htm
La Nina:
http://www.pmel.noaa.gov/toga-tao/la-nina-story.html
http://www.pmel.noaa.gov/toga-tao/la-nina-story.html
Intensity:
http://www.crh.noaa.gov/arx/enso.html
http://www.pmel.noaa.gov/toga-tao/el-nino-winters.html
