Climate Model Summary
Positive IOD likely to be dominant driver until end of spring
The Indian Ocean sea surface temperature (SST) pattern remains consistent with a positive IOD (Indian Ocean Dipole) event. This is also reflected in cloud and wind patterns in the tropical Indian Ocean. While the IOD index has fluctuated somewhat in recent weeks, the broader SST pattern in the Indian Ocean has remained positive IOD-like since the end of May.
The most recent weekly IOD index value is well above the positive threshold, and model outlooks suggest this pattern is likely to persist through to the end of the southern hemisphere spring. A positive IOD typically means below average winter–spring rainfall for much of southern and central Australia.
The El Niño–Southern Oscillation (ENSO) is currently neutral. Sea surface temperatures in the key ENSO region of the tropical Pacific are close to average, having hovered around the threshold for much of autumn and early winter. The latest outlooks from the surveyed models suggest that ENSO-neutral is the most likely scenario for the remainder of 2019.
The latest weekly NINO3.4 value to 18 August is +0.2 °C, meaning the central tropical Pacific Ocean remains within neutral-ENSO bounds. All but one of the eight surveyed models suggest the central tropical Pacific (NINO3.4) is likely to remain neutral with respect to the El Niño–Southern Oscillation (ENSO) from September through to the end of 2019. One model suggests La Niña thresholds may be reached by the end of the year, but this model is an outlier, and model accuracy decreases towards the end of the outlook period.
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
Sea surface temperatures in the Indian Ocean have shown patterns consistent with a positive IOD event since the end of May. While the IOD index has as fluctuated around the positive IOD threshold in recent weeks, the latest weekly value (to 18 August) is well above the threshold at +0.8 °C. This is a result of cooler than average ocean temperatures off the Java coast and warmer than average temperatures off the Horn of Africa.
All models suggest positive IOD index values are likely to persist until the end of spring. IOD events typically dissipate by summer as the monsoon trough moves into the southern hemisphere. For 2019 to be considered a positive IOD year, positive values would generally need to be sustained for at least eight weeks.
A positive IOD typically means a drier than average winter-spring for parts of southern and central Australia. It also typically means warmer than average winter-spring days for the southern two-thirds of Australia and early start to the southern bushfire season. Persistent IOD index values above +0.4 °C typically indicate a positive IOD event, while values below −0.4 °C typically indicate a negative IOD event.
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 17 August) suggests the central tropical Pacific will remain close to average throughout the outlook period. For the Indian Ocean Dipole (IOD), the Bureau's model suggests positive IOD values are likely to persist throughout spring, peaking in September.
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.