Climate Model Summary
Positive IOD may be underway
The latest model outlooks and recent observations suggest the Indian Ocean may be in the early stages of a positive phase of the Indian Ocean Dipole (IOD). The IOD index has been above the positive threshold for three consecutive weeks and model outlooks suggest a positive phase is likely for the remainder of the austral winter and into spring. A positive IOD typically means below average winter–spring rainfall for much of southern and central Australia.
While sea surface temperatures in the key ENSO region of the tropical Pacific have been close to El Niño thresholds since late February, the atmosphere has shown an inconsistent response. The latest outlooks from the surveyed models suggest that sea surface temperatures in this region are likely to cool, shifting away from El Niño thresholds during winter, but remain warmer than average. Three models show a resumed warming in spring, touching on, or just exceeding, El Niño thresholds in October and/or November while the remaining five models maintain neutral values through the spring months.
The latest weekly NINO3.4 value to 9 June is +0.8 °C, meaning the central tropical Pacific Ocean is right on the El Niño threshold. Four of the eight surveyed models suggest the central tropical Pacific (NINO3.4) is likely to be at or above El Niño thresholds in July, but by August all models show neutral (though warmer than average) values are likely. Three models indicate subsequent warming during spring, touching on El Niño thresholds in October and/or November, while the other five remain neutral. This will be monitored closely over the coming months.
El Niño typically means a drier than average winter-spring for much of eastern Australia. 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
The Indian Ocean Dipole (IOD) index is recording its third week above the positive IOD threshold, with the latest weekly value (to 9 June) at +0.7 °C. Five of six models suggest positive IOD index values are likely through to the end of spring. For 2019 to be considered a positive IOD event, the current values would 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. 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 8 June) suggests the central tropical Pacific will persist near the El Niño threshold for much of the outlook period, but dip into neutral values towards the end of winter and early spring.
For the Indian Ocean Dipole (IOD), the Bureau's model suggests positive IOD values are likely to persist throughout winter and spring.
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.