Climate Model Summary
Models suggest negative IOD may develop from mid-winter
The Indian Ocean Dipole (IOD) is currently neutral but the latest model outlooks indicate a negative IOD could develop during the southern winter. A negative IOD typically brings above average winter–spring rainfall to southern Australia.
The El Niño–Southern Oscillation (ENSO) is also neutral. Latest outlooks from the surveyed models suggest that an ENSO-neutral state is the most likely scenario until the end of winter 2020. However, some models are suggesting the development of La Niña could occur in mid-spring.
These outlooks will be monitored closely over the coming weeks, as ENSO and IOD predictions made during autumn tend to have lower accuracy than predictions made at other times of year.
The latest weekly NINO3.4 value to 24 May 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 cool during the southern winter and early spring. While most models predict NINO3.4 will remain within neutral bounds, three models suggest La Niña thresholds could be met or exceeded by October 2020.
It should be noted that ENSO predictions made during autumn tend to have lower accuracy than predictions made at other times of the year. This means that current ENSO forecasts should be viewed with some caution. Forecast accuracy improves with outlooks issued in winter.
Indian Ocean Dipole (IOD) outlook
The IOD is currently neutral. The latest value for the week ending 10 May is +0.3 °C. Model outlooks indicate the IOD is likely to become negative over the coming months, with 4 out of 6 models exceeding the negative IOD threshold from July.
IOD predictions made during autumn tend to have low accuracy compared to predictions made at other times of the year, and most individual models show a wide spread of possible scenarios across the ensemble members. Recent variation in outlooks by some models reinforces the need to be wary with IOD predictions at this time of the 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 23 May 2020) suggests sea surface temperatures in the central tropical Pacific (NINO3.4) will cool over the coming months, potentially reaching the La Niña threshold by September.
For the Indian Ocean Dipole (IOD), the Bureau's model indicates the IOD index values will now not exceed the negative IOD threshold during the outlook period. Recent variation in model outlooks by ACCESS-S reflect the low predictability of the IOD at this time of year.
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.