A comparison of the 2015 and 1997 El Niños. Credit: NASA’s Earth Observatory.
Levine, A. F. Z., and M. J. McPhaden (2016), How the July 2014 Easterly Wind Burst Gave the 2015-6 El Niño a Head Start, Geophys. Res. Lett., 43, doi:10.1002/2016GL069204.
Following strong westerly wind bursts in boreal winter and spring of 2014, both the scientific community and the popular press were abuzz with the possibility of a major El Niño developing, but the widely anticipated major 2014-5 El Niño event didn't even qualify as an El Niño by conventional definitions.
The boreal summer easterly wind burst inhibited the growth of the El Niño event, and also prevented and then reversed the discharge of the equatorial heat content that typically occurs during the course of an El Niño event. This head start of equatorial heat content helped push the 2015-6 El Niño event to extreme magnitude.