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 New South Wales have been warned to prepare for wild weather overnight as a low-pressure system from Tasmania gets set to batter northern parts of the state.
Three adults and two young children have been rescued by helicopter after becoming trapped in floodwaters in Huonville, south-east of Tasmania.
Power may not be restored to Eyre Peninsula homes until the early hours of the morning after twin tornadoes and wild weather caused significant damage to transmission towers in South Australia.