Climate Model Summary
La Niña has passed its peak
La Niña continues in the tropical Pacific Ocean. Along with atmospheric and oceanic indicators, surveyed model outlooks indicate that this La Niña event has passed its peak and is weakening, however, its impacts are expected to continue into early autumn. All models forecast a return to a ENSO neutral phase during autumn. La Niña typically increases the likelihood of above average rainfall across much of northern and eastern Australia during early autumn.
The Indian Ocean Dipole (IOD) is neutral with models favouring a neutral outlook for the coming months. IOD events are typically unable to form between December and April. This is because the monsoon trough shifts south over the tropical Indian Ocean, changing wind patterns which prevents the IOD pattern from being able to influence the Australian region. The IOD therefore has little effect on Australian climate at this time of year.
The latest weekly NINO3.4 value to 28 February is −0.8 °C, which is just on the La Niña threshold. All the surveyed models indicate central Pacific sea surface temperatures (NINO3.4) have passed their peak 'La Niña' related cooling, and forecast a return to a neutral ENSO phase by the middle of the austral autumn. However, despite the easing, typical La Niña impacts (enhanced rainfall across much of eastern and northern Australia) are likely to be felt for the remainder of the southern summer and early autumn.
Indian Ocean Dipole (IOD) outlook
The IOD is currently neutral. The latest value for the week ending 28 February is −0.15 °C. All models except one indicate the IOD will remain neutral throughout the outlook period.
Indian Ocean Dipole events are typically unable to form between December and April. This is because the monsoon trough shifts south over the tropical Indian Ocean, changing wind patterns which prevents the IOD pattern from being able to influence the Australian region. The IOD therefore has little effect on Australian climate at this time of year.
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 27 February 2021) indicates sea surface temperatures in the central tropical Pacific (NINO3.4) are likely to warm during the outlook period, and remain within neutral thresholds during autumn. This outlook indicates La Niña is weakening and will end during autumn, however La Niña-related impacts (wetter than average conditions in eastern and northern Australia) are likely to continue into early autumn.
For the Indian Ocean Dipole (IOD), the latest model run indicates IOD index values are likely to remain neutral until at least the end of the southern hemisphere autumn. The IOD typically has little impact on Australian climate from December to April, while the monsoon trough is in the southern hemisphere.
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.