Climate Model Summary

Climate Model Summary Archive: May 2014

El Niño remains likely for 2014

While the El Niño-Southern Oscillation (ENSO) is currently neutral, patterns in the tropical Pacific Ocean and atmosphere are consistent with the early stages of a developing El Niño. Despite two climate models (BoM and MeteoFrance) easing their prediction slightly over the past month, all but one of the eight surveyed models indicate an El Niño is likely to develop by the southern hemisphere spring.

El Niño is often, but not always, associated with below-average rainfall during the second half of the year across large parts of southern and inland eastern Australia. Daytime temperatures also tend to be above average over southern Australia.

The Indian Ocean Dipole (IOD) is also neutral. Current model outlooks suggest the IOD will remain neutral throughout winter, but are showing a weak trend towards a positive IOD in spring. A positive IOD event increases the chance of below average rainfall across much of central and southern Australia, and can therefore exacerbate rainfall impacts should it coincide with an El Niño event.

NINO3.4 outlook

The latest NINO3.4 forecasts (initialised in May) indicate the tropical Pacific Ocean is likely to continue warming over the coming months. Most models indicate sea surface temperatures in the central tropical Pacific will be above or close to El Niño thresholds by August, with all but one exceeding the threshold by October. Four models show NINO3.4 values considerably higher than the El Niño threshold by the end of the forecast period.

The range in forecast values of NINO3.4 is quite wide when considering individual ensemble members (forecast scenarios) from each model with values ranging between 0.0 °C and +3.0 °C by October. (See the 'Models' tab for links to individual model output for NINO3.4).

The most recent NINO3.4 value is +0.5 °C for the week ending 11 May 2014. Sustained NINO3.4 values above +0.8 °C indicate El Niño conditions.

Indian Ocean Dipole (IOD) outlook

The IOD index remains neutral with a latest weekly value of –0.1 °C for the week ending 11 May 2014. The chance of a positive IOD event is elevated during El Niño events which can exacerbate rainfall reductions resulting from the El Niño. Although remaining neutral throughout the forecast period, the models are showing a slight trend towards a positive IOD developing in spring.

The following graph shows 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.

Predictive Ocean Atmosphere Model for Australia (POAMA)

POAMA, run at the Bureau of Meteorology, generates an eight-monthly forecast on the first day of each month. The most recent model run (started in May) predicts NINO3.4 is likely to just exceed El Niño thresholds around July and remain very close to the threshold throughout the forecast period. The following forecast values (at the top of the table) are for the ensemble mean.

POAMA archive data is available here.

ENSO Dials

The arrows on the dials below indicate the combined average ofmonthly NINO3.4 outlooks from a survey of international global climate models. Note that the individual model runs vary around the average.

ENSO dial month+1 ENSO dial month+3 ENSO dial month+5

NINO3.4 outlook bar-graphs

The following graphs shows 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.

NINO3.4 bar graph month+1 NINO3.4 bar graph month+3 NINO3.4 bar graph month+5

IOD outlook bar-graphs

The following graph shows 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.

IOD bar graph month+1 IOD bar graph month+3 IOD bar graph month+5

Past climate model summaries