[Dr. Michael McPhaden] El Nino and La Nina are predictable. In fact they are the most predictable climate phenomenon on the planet, other than the normal march of the seasons. The first successful prediction of an El Nino was in 1986 by Mark Cane and his group at Lamont-Doherty Earth Observatory. Now there are about 20 groups worldwide that routinely issue ENSO forecasts. The models that are used are not perfect, of course, just like weather prediction models are not perfect. But they do show skill out to about 6 to 9 months. And the source of predictability for El Nino, one important source, perhaps the most important source, lies in the slow evolution of upper ocean heat content. [Narrator] The upper ocean heat content that is used for El Nino prediction is the volume of warm water in a band along the equator in the tropical Pacific Ocean. The buildup of excess heat content along the equator is a necessary precondition for El Nino to occur. You can see that the heat content, in red, builds up prior to all El Ninos, in blue, over the past 30 years. When the heat content reaches a certain threshold, it significantly increases the likelihood for an El Nino to occur. Winds and currents during the El Nino event purge the excess heat to higher latitudes, which terminates the event. The time between El Ninos is determined by the time to "recharge" by ocean currents under strong trade wind forcing building up the excess heat content that is necessary for initiation of another El Nino. The importance of heat content as a predictor for El Nino and La Nina is a key element of the Recharge Oscillator Theory. [McPhaden] Here is the compilation of the 20 groups worldwide, the forecast for the coming seasons. This is compiled by the International Research Institute for Climate and Society. What's on this axis is the NINO3.4 index of sea surface temperature. Time is over here. This is the neutral zone, where you could say either El Nino or La Nina. A forecast that was below this would be for La Nina, and a forecast above this is for El Nino. [Narrator] In mid-October 2015, the forecaster consensus unanimously favored a strong El Nino.