Why? Because of a lesser know but equally if not more powerful weather altering oceanic event called the Pacific Decadal Oscillation (or PDO for short). What is the PDO:
The Pacific Decadal Oscillation (PDO) is a robust, recurring pattern of ocean-atmosphere climate variability centered over the mid-latitude Pacific basin. During a “warm”, or “positive”, phase, the west Pacific becomes cooler and part of the eastern ocean warms; during a “cool” or “negative” phase, the opposite pattern occurs.
How does the PDO effect El Nino? Simply put, it has the potential to increase the severity of El Nino cycles. “Warmer sea surface temperatures in the northern Pacific during the positive PDO phase tend to amplify El Nino’s effects.” The fluctuations in PDO are longterm so the potential for many consecutive El Ninos of increased strength is there. With the word Decadal in the term we may jump to the conclusion that we are in for a 10 year stretch but that can not be predicted with absolute accuracy.
So if you thought El Nino was a buzzword thrown around liberally prepare yourself for Mega El Ninos due to warm PDO phase.
Here is a pretty dry scientific video that will get you up to speed on PDO: