Climate Model Summary
Ocean temperatures reach El Niño thresholds, but atmosphere yet to collaborate
Sea surface temperatures (SSTs) in the tropical Pacific Ocean have recently reached El Niño thresholds. Most model outlooks suggest these warmer than average SSTs will be maintained throughout the austral summer. However, atmospheric indicators of El Niño remain neutral, indicating the ocean and atmosphere are not yet coupled (i.e. not reinforcing each other to help sustain the El Niño state).
A positive Indian Ocean Dipole (IOD) event has been active since early September. Most models indicate the IOD is likely to return to neutral by early summer, consistent with the typical IOD event life-cycle.
An El Niño in summer increases the possibility of a dry and warm end to the year in parts of Australia. It also raises the risk of heatwaves and bushfire weather in the south, but reduces the risk of tropical cyclone activity in the north.
The tropical Pacific Ocean is warmer than average, across almost all of the equatorial region. The latest weekly NINO3.4 anomaly (to 2 December) is +0.9 °C, just exceeding El Niño thresholds for the fourth consecutive week.
All surveyed models predict the tropical Pacific Ocean will remain above El Niño thresholds throughout November and December. By February, one model drops just below El Niño thresholds.
Although sea surface temperatures (SSTs) are above El Niño thresholds, atmospheric indicators of El Niño remain neutral, indicating the ocean and atmosphere are not yet coupled (i.e. not reinforcing each other to sustain the El Niño state).
Note: The climate models used in this survey only assess oceanic indicators of ENSO (i.e. SSTs), not atmospheric indicators. Hence SST outlooks/observations that exceed the El Niño threshold, don't directly translate to an event declaration; sustained warming in the NINO SST regions and coupling with the tropical Pacific atmosphere also need to be observed.
Persistent NINO3.4 values above +0.8 °C typically indicate El Niño, while values below −0.8 °C typically indicate La Niña.
Indian Ocean Dipole (IOD) outlook
A positive Indian Ocean Dipole (IOD) event has been active since early September 2018. The most recent weekly index value (to 1 December) is +0.3 °C, dipping just below the positive IOD threshold. Most models suggest IOD index values are likely to return to neutral by early summer.
A positive IOD event typically reduces winter and spring rainfall in central and southern Australia and can exacerbate any El Niño driven rainfall deficiencies. The IOD typically has little influence on Australian climate from December to April.
Australian Community Climate Earth-System Simulator–Seasonal (ACCESS–S)
The Bureau of Meteorology's climate model generates a six-month forecast for the NINO and IOD indices each fortnight.
The most recent model run (generated 1 December) indicates the central tropical Pacific will remain above the El Nino threshold throughout the outlook period. For the IOD, the Bureau's model suggests the positive IOD event currently underway will decay in December.
The forecast values, shown below in bold, are for the model's ensemble mean.
Product code: IDCKGL0000
Average of international model outlooks for NINO3.4
Average of international model outlooks for the Indian Ocean Dipole (IOD)
The arrows on the dials indicate the combined average of monthly outlooks from a survey of international global climate models. Note that the individual model runs vary around the average.
NINO3.4 covers the central Pacific region.
The graphs are based on the ensemble mean for the most recent model run.
These graphs show the average forecast value of NINO3.4 for each international model surveyed for the selected calendar month. If the bars on the graph are approaching or exceeding the blue dashed line, there is an increased risk of La Niña. Similarly, if the bars on the graph are approaching or exceeding the red dashed line, there is an increased chance of El Niño.
The graphs are based on the ensemble mean for the most recent model run.
Thse graphs show the average forecast value of the IOD index for each international model surveyed for the selected calendar month. If the majority of models are approaching or exceeding the blue dashed line, then there is an increased risk of a negative IOD event. If the majority of models are approaching or exceeding the red dashed line, then there is an increased risk of a positive IOD event.
Sea surface temperature graphs
NINO34 predictions for the next 5 months.
About these sea surface temperature outlooks
About the graphs
The plume graphs show outlook scenarios for sea surface temperatures (SSTs) averaged over particular regions of the Pacific and Indian oceans. The SSTs in these regions are related to different phases of the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD); climate drivers that can influence Australian rainfall and temperature patterns.
The graphs show 99 possible scenarios (grey lines), that are produced by the Bureau's climate outlook model, which represent the range of outcomes that may occur over the forecast period. For example, they may show the SSTs in the NINO3.4 region to be warming, cooling, or remaining mostly steady. At times the outlook might suggest a shift towards (or away from) values typically associated with El Niño or La Niña events. Each of the 99 scenarios is based on current conditions in the global oceans/atmosphere and how the model anticipates their likely development over the outlook period, with each given slightly different treatment to provide a range of likely possibilities. This technique allows us to see the range of what is possible, with a small spread in the range of scenarios meaning more confidence in the likely path, and a larger spread meaning less confidence.
The green line is the average of all these 99 scenarios, often known as the ensemble mean. The solid black line shows the observations (based on the Bureau's SST observation analysis for each region) for the previous months.
The graphs are updated fortnightly. As a result, the value given for the 'current month' can vary depending on at what point in the month the forecast is being issued. Forecasts made on the 1st to the 11th of the month show a forecast value for the current month. For forecasts made after the 11th of the month, a month-to-date observation (shown by an open circle and dashed line), based on weekly observational data, will be used for the current month as a preliminary value until the final monthly data is available.
About the maps
While the climate model runs a set of 99 possible scenarios, it can be useful to look at the ensemble mean (the average of these forecasts) to see the most likely scenario. The global SST maps show the most likely SST anomaly for the months and seasons ahead. This can be useful to see how ENSO and IOD look spatially. The SST anomalies show the difference from the 1990-2012 average (often referred to as the base period).
About the outlook model
The long-range SST outlooks are generated by the Bureau's climate model, ACCESS–S (Australian Community Climate Earth-System Simulator–Seasonal). ACCESS–S is the Bureau of Meteorology's dynamical (physics-based) weather and climate model used for monthly, seasonal and longer-lead climate outlooks. Prior to August 2018, climate outlooks (including these graphs) were produced by the Bureau's earlier model, POAMA.
Product code: IDCK000073
The models used within our survey are listed below with links to their agency homepages, model output and technical information about the model.
Model data are provided for Bureau of Meteorology use by the agencies detailed in the Models section. Respective agency copyright applies to these data.