Climate Model Summary
Models suggest further warming towards El Niño
Tropical Pacific sea surface temperatures are neutral with respect to the El Niño–Southern Oscillation (ENSO), but latest model outlooks and ocean/atmosphereic observations suggest the chance of El Niño thresholds in 2018 has increased. Most models suggest continued warming of the tropical Pacific is likely, with four out of eight models exceeding El Niño thresholds by the end of 2018. Two additional models fall just short of El Niño thresholds by December.
El Niño is often, but not always, associated with below average rainfall across eastern and northern Australia during winter-spring. In summer, this drying influence contracts to tropical regions of Australia, although the possibility of elevated temperatures elsewhere remains high.
The Indian Ocean Dipole (IOD) has shown signs of an emerging positive IOD event in recent weeks. Four of six climate models suggest that the positive IOD threshold may be exceeded in October, but most suggest a return to the neutral IOD range by December.
The El Niño–Southern Oscillation (ENSO) remains neutral. The most recent weekly NINO3.4 anomaly (to 7 October) has risen to +0.7 °C, increasing by almost half a degree over the last fortnight and is now just shy of El Niño thresholds.
Most surveyed models predict the tropical Pacific Ocean will continue to warm in the coming months. By December, four of eight models indicate that NINO3.4 will have reached values consistent with El Niño. Two additional models fall just shy of El Niño thresholds while the remaining two models maintain neutral conditions until the end of the year. El Niño onset at this time of year would be later than usual, although not unprecedented.
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
The Indian Ocean Dipole (IOD) is showing signs of an emerging positive IOD event. The most recent weekly IOD index value (to 7 October) is +0.6 °C; the fourth consecutive week in the positive IOD range. Four of the six models suggest positive IOD thresholds will continue into October, but most drop back to neutral IOD levels by December.
A positive IOD event typically reduces winter–spring rainfall in central and southern Australia, and can exacerbate any potential 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 6 October) indicates the central tropical Pacific will warm, with NINO3.4 temperatures meeting El Niño thresholds during October and maintaining them throughout summer. For the IOD, the Bureau's model suggests the index will continue to exceed the positive IOD threshold in October and return to neutral values by summer.
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.