Earlier this year, it really did look like a strong El Niño would emerge.
A series of winds that begin in the Indian Ocean — known as the Madden-Julian Oscillation — began blowing eastward, counteracting and weakening those trade winds in the Pacific. That allowed some of that warm water piled up near Indonesia to start sloshing back toward the east.
As a result, by June, sea temperatures in the central equatorial Pacific (the Niño 3.4 region) had risen 0.5°C above their historical average. It looked like an El Niño was on the way.
But then… things got messy. Atmospheric conditions over the Pacific Ocean didn't shift as expected. Specifically, scientists weren't seeing the change in atmospheric pressure over both the eastern and western Pacific that you'd expect during an El Niño. (See this blog postfrom NOAA for a fuller explanation.)
In August, Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research, told me that the waters in the western Pacific hadn't cooled off as quickly as expected — so we didn't seen the sort of west-to-east temperature gradient that can sustain a strong El Niño.
More @ Vox
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