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.
Some people affected by Cyclone Debbie say they are frustrated they have not been able to return to their damaged properties in north Queensland.
South-east Queensland is set for a drenching on Thursday with rainfall in excess of 200 millimetres possible in some localised areas, the Bureau of Meteorology (BOM) has warned.
As emergency services build a picture of the destruction wrought by Cyclone Debbie, 61,000 remain without power and Mackay may have only 24 hours of clean water remaining.