Ever since early 2014, scientists have been expecting this latest El Niño to form. But, in a sign of how slippery the system can be, El Niño kept defying predictions and not showing up.
Finally, in March 2015, after a number of false starts, scientists at NOAA's climate prediction center were ready to declare that a weak El Niño was underway. Specifically, sea surface temperatures in that Niño 3.4 region (roughly in the center of the chart below) had been at least 0.5°C above their baseline since September. And, importantly, atmospheric conditions were responding in turn, with more rain over the central Pacific and less rain over Indonesia:
At the time, however, NOAA's forecasters said that this El Niño looked "weak," with possibly minimal effects on global weather patterns, and only had a 50 to 60 percent chance of lasting through the summer.
Then, somewhat unexpectedly, El Niño got stronger and stronger. By August 2015, sea surface temperatures had soared to more than 1.2°C above baseline in the Niño 3.4 region, and scientists were seeing the resulting telltale atmospheric changes. Here's a chart from July and August — notice how the anomalous warm area has moved eastward since March:
NOAA's Climate Prediction Center is now estimating that there's a 90 percent chance El Niño will persist through the fall/winter. And when it peaks, signs suggest that this could be an extremely strong event, rivaling the strongest El Niños since detailed records began in 1950. Some forecasters have even dubbed this one a potential "Godzilla."
Over at NOAA's ENSO blog, Emily Becker offers a more detailed breakdown of why forecasters are betting on a powerful, possibly record-setting, El Niño. Keep in mind that forecasts often go awry, that surprises occur regularly, and we can't be perfectly certain of how things will turn out. Still, she writes, "We have a relatively confident forecast for a strong event."