That is, according to the Oceanic Niño Index (ONI), the 3-month running mean of ERSST.v5 SST anomalies in the Niño 3.4 region (5°N-5°S, 120°W-170°W)].
5 consecutive months of ONI ≥ 0.5 is considered to be an El Nino. The last five months have barely slipped under that line:
It's not quite as strong as last winter's El Nino, but it does help explain why this winter's temperatures are or are bordering on new highs. (But not why they're on par with, or exceeding, the winter of 2015-2016's El Nino.)
And if this was a significant El Nino, we wouldn't be seeing record breaking ocean heat content.