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.
About 9,000 properties remain without power in Perth and Western Australia's south-west after damaging winds brought down trees and debris, with a severe weather warning still in place for parts of the state.
The South Australian towns of Virginia and Port Wakefield are under threat from floodwaters as the Gawler and Wakefield rivers burst their banks, with warnings more rain is on the way.
An evacuation order has been issued for low-lying areas of Condobolin in the central west of New South Wales, as flood peaks in the Lachlan River move downstream.