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.
The Katherine River is set to flood as an active monsoon trough causes heavy rains and squally showers across the Northern Territory, registering the wettest day in five years.
The monsoon trough has redeveloped over northern Australia this week, bringing Darwin its heaviest rain five years.
As the mercury soars in Sydney today, spare a thought for the people of Moree in northern New South Wales, who are in the midst of a record-breaking heatwave.