Climate Model Summary
Increasing chance of La Niña in spring; negative IOD less likely
The El Niño–Southern Oscillation (ENSO) is neutral, but models suggest cooling in the central tropical Pacific towards La Niña thresholds is likely to continue. In line with this, the Bureau activated a La Niña WATCH in mid-June. While an ENSO-neutral state is the most likely scenario until the end of winter 2020, several models suggest La Niña thresholds could be exceeded in early spring with five models (more than half surveyed) exceeding threshold by the end of spring. La Niña events typically enhance spring rainfall in northern, central and eastern Australia.
The Indian Ocean Dipole (IOD) is currently neutral. Two of the surveyed models indicate a negative IOD could develop in late-winter or early-spring, with a third just touching on thresholds later in spring, but the remainder favour neutral conditions to persist. A negative IOD typically brings above average winter–spring rainfall to parts of southern and central Australia.
These outlooks and ENSO/IOD indicators will be monitored closely over the coming weeks for further signs of development towards an event.
The latest weekly NINO3.4 value to 2 August is −0.3 °C, consistent with a neutral state of the El Niño–Southern Oscillation (ENSO). All surveyed models indicate the central tropical Pacific (NINO3.4) will continue to cool, with temperatures likely to drop below average in late July / early August. Three models suggest cooling in the coming months could see La Niña thresholds being met by September 2020, with two additional models meeting thresholds by the end of the southern spring.
The remaining three models also suggest cooling in the coming months, but remain shy of La Niña thresholds (i.e. ENSO-neutral). It is possible for La Niña influences to be felt in Australia (above average spring rainfall in eastern, northern and southern Australia), even if NINO3.4 thresholds for La Niña aren't quite met.
Indian Ocean Dipole (IOD) outlook
The IOD is currently neutral. The latest value for the week ending 2 August is +0.3 °C. Two of the six surveyed models indicate the IOD could exceed negative IOD thresholds by late-winter or early-spring, with a third model touching on thresholds from mid-spring. The remaining three models expect the IOD to remain neutral throughout the outlook period. A negative IOD typically enhances winter–spring rainfall over parts of southern and central Australia.
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 August 2020) suggests sea surface temperatures in the central tropical Pacific (NINO3.4) will cool over the coming months, exceeding La Niña thresholds from October.
For the Indian Ocean Dipole (IOD), the latest model run indicates IOD index values are likely to remain neutral throughout the outlook period.
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.