The eastern equatorial Pacific box (5° N-5° S, 150-90° W). The Japan Meteorological Agency defines El Nino with it.
Indices
Nino 3 covers the eastern half of the equatorial Pacific. It was the main El Nino index before Nino 3.4 took over at NOAA. The Japan Meteorological Agency (JMA) still uses it: see JMA El Nino outlook (Japan).
In September 2026 the CPC reported Nino 3 at +2.5 °C.