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.
Tropical Cyclone Debbie has intensified to category four and is expected to hit the north Queensland coast on Tuesday morning, the Bureau of Meteorology (BOM) has warned.
Engineers are frantically working to solve engine problems on the Royal Australian Navy's two largest ships, with fears the Landing Helicopter Docks (LHDs) could be out of action for several weeks.
As Tropical Cyclone Debbie strengthens off the coast near Townsville in north Queensland, residents are being warned to prepare for the worst storm to hit the state since Cyclone Yasi in 2011.