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.
Panicked residents in areas affected by Cyclone Debbie have relayed their experiences to the ABC as torrential rain and wind gusts pummel the region.
The full devastation brought on by Tropical Cyclone Debbie will not be known until Wednesday morning, Queensland Premier Annastacia Palaszczuk has warned, as the system is further downgraded to a category two.
Cyclone Debbie has been downgraded to a category two system after crossing the north Queensland coast.