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.
BSES and weather bureau officials are due to meet today to prepare for heavy rain forecast for later this week across Adelaide and the Adelaide Hills.
New South Wales Premier Mike Baird has toured the flood-hit town of Forbes, in the state's central west, where he has thanked State Emergency Service (SES) volunteers for their efforts.
It has been already a big month of weather across southern and eastern Australia, although the worst is yet to come for some areas.