Guest Post by Bob Tisdale
The weekly sea surface temperature anomalies for the four NINO regions across the equatorial Pacific were at or above the +1.0 deg C threshold of a moderate El Niño, based on data for the week centered on April 22, 2015.
The source of the data is the NOAA Monthly Atmospheric & SST Indices webpage, specifically here. The anomaly data are referenced to the WMO-preferred base years of 1981-2010. NOAA defines a moderate El Niño as an “Episode when the peak Oceanic Niño Index (ONI) is greater than or equal to 1.0°C and less than or equal to 1.4°C.” See the footnotes in the NOAA ENSO Blog post here. The NOAA Oceanic NINO Index is based on the sea surface temperature anomalies of the NINO3.4 region.
On the other hand, the 30-day and 90-day averages of the preliminary BOM Southern Oscillation Index are in ENSO-neutral levels, well shy of their El Niño threshold of -8.0.
I’ll provide a more-detailed ENSO update in a few weeks.