The NINO3.4 index is one of several El Niņo/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 Niņo 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 Niņo or La Niņa event is identified if the 5-month running-average of the NINO3.4 index exceeds +0.4°C for El Niņo or -0.4°C for La Niņa for at least 6 consecutive months.
Adelaide residents are preparing for heavy rain, high seas and strong winds forecast to hit later this week, in what the SES says could be one of the most significant weather events it has seen in South Australia.
Forbes has been declared a natural disaster zone after the region was hit by flooding over the weekend.
Further rain expected in the central west of New South Wales could see the Lachlan River at Forbes reach a higher peak, despite it already being inundated with the greatest water levels in 25 years.