Just in case you missed the mention of this in the text of the most recent sea surface temperature update…
In a June 2015 post, we discussed and illustrated how Weak El Niños and La Niñas Come and Go from NOAA’s Oceanic NINO Index (ONI) with Each SST Dataset Revision. NOAA has once again revised their Oceanic NINO Index. Now they’re using the base years of 1986-2015 for the NINO3.4 sea surface temperature data starting in 2001, instead of 1981-2010. See the NOAA webpage here for the basis of using shifting base years for their Oceanic NINO Index. Based on the date of that webpage it appears the recent changes took place in June 2016.
The recent changes have shifted the start and end months of some the “official” NOAA El Nino and La Niña events. But the most noticeable change is the resurrection of the 2014/15 El Niño. See Table 1 where I’ve highlighted the relative time period for the 3 most-recent versions of the Oceanic NINO Index.
Table 1 (Click for full-sized table)
The 2014/15 El Niño registered on ONI when NOAA used their ERSST.v3b sea surface temperature data and the shifting base years, where the base years of 1981-2010 were used for the most recent years (link here). Then in June 2015 NOAA switched to their “pause-buster” ERSST.v4 sea surface temperature data for the Oceanic NINO Index (link here), again using 1981-2010 as base years for the most recent data–the 2014/15 El Niño disappeared with the “pause-buster” data. And now, with the use of the base years of 1986-2015 for the ONI data starting in 2001 (link here), the 2014/15 El Niño has reappeared as an “official” event.
Once again NOAA has shown that weak El Niños and La Niñas can come and go from their Oceanic NINO Index (ONI) with each revision, and once again, by constantly changing the Oceanic NINO Index, NOAA is showing, very obviously, that their listing of “official” ENSO events has little value.