The NINO3.4 index is one of several El Niño/Southern Oscillation (ENSO) indicators based on sea surface temperatures.
NINO3.4 is the average sea surface temperature anomaly in the region bounded by 5°N to 5°S, from 170°W to 120°W. This region has large variability on El Niño time scales, and is close to the region where changes in local sea-surface temperature are important for shifting the large region of rainfall typically located in the far western Pacific.
An El Niño or La Niña event is identified if the 5-month running-average of the NINO3.4 index exceeds +0.4°C for El Niño or -0.4°C for La Niña for at least 6 consecutive months.
Parts of Victoria have already received almost double the average rainfall this month, and some areas have recorded the wettest April in 16 years.
New Zealanders are bracing for a week of wild weather.
The skies above New South Wales farms have been filled with smoke in recent weeks as growers burn a huge load of dry stubble left over from last year's record crop yields.