Climate Model Summary
Positive IOD strengthens, but influence likely to weaken in early summer
The positive IOD (Indian Ocean Dipole) has gained strength over the past month and is likely to maintain strong positive values until at least the end of spring. A positive IOD typically means below average winter–spring rainfall for much of southern and central Australia.
IOD events are unable to form, and therefore influence Australian climate, during the summer months once the monsoon trough transitions into the southern hemisphere, typically from December to April. As a result, the prolonged and widespread dry signal over much of Australia during 2019 (related to this strong positive IOD event) is likely to weaken during summer.
The El Niño–Southern Oscillation (ENSO) is currently neutral. The latest outlooks from the surveyed models suggest that an ENSO-neutral state is the most likely scenario for the remainder of 2019 and into the first quarter of 2020.
The latest weekly NINO3.4 value to 13 October is +0.5 °C, within the ENSO-neutral range. All eight surveyed models suggest the central tropical Pacific (NINO3.4) is likely to remain neutral through to at least February 2020.
An ENSO-neutral state means that the El Niño–Southern Oscillation has little influence on Australian or global climate.
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, with the index exceeding the positive IOD threshold from mid-July. The latest value for week ending 13 October is +2.2 °C, well above the +0.4 °C threshold and the highest IOD weekly index value since at least 2001, and possibly since 1997. This is a result of cooler than average sea surface temperatures off Indonesia and warmer than average temperatures off the Horn of Africa.
All models suggest positive IOD index values are likely to persist into early summer, however, IOD events are unable to form (and therefore influence Australian climate) once the monsoon trough moves into the southern hemisphere, usually from December to April.
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 an 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 12 October) suggests the central tropical Pacific sea surface temperatures will remain neutral 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 October and returning to average during the southern 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.