Notice: Because of the high frequency filter applied to
the ERSSTv4 data (Huang et al. 2015, J.Climate), ONI values may change up to two months after the initial "real time" value is
posted. Therefore, the most recent ONI values should be considered an estimate.
DESCRIPTION: Warm (red) and cold (blue) periods based on a threshold
of +/- 0.5oC for the Oceanic Niño Index (ONI) [3 month running mean of ERSST.v4 SST anomalies in the Niño 3.4
region (5oN-5oS, 120o-170oW)], based on
30-year base periods updated every 5 years.
For historical purposes, periods of below and above normal SSTs are colored in blue and red when the threshold is met for a
minimum of 5 consecutive overlapping seasons. The ONI is one measure of the El Niño-Southern Oscillation, and other indices
can confirm whether features consistent with a coupled ocean-atmosphere phenomenon accompanied these periods.