Climate Model Summary

Climate Model Summary Archive: September 2013

ENSO and IOD neutral

Neutral conditions persist in the tropical Pacific. All of the international climate models surveyed by the Bureau of Meteorology indicate that this neutral state will persist throughout the remainder of spring and into summer.

In the tropical Indian Ocean, the negative Indian Ocean Dipole (IOD) event has weakened considerably over the past several weeks, with neutral values persisting since early August. The majority of the international models indicate these neutral values are likely to persist, suggesting that the 2013 negative IOD is most likely at an end. Two models suggests a brief return to the negative IOD values.

NINO3.4 Outlook

The latest NINO3.4 forecasts (initialised in September) from all seven of the surveyed models indicate neutral El Niño-Southern Oscillation (ENSO) conditions are likely to persist through to early 2014. Most models suggest the NINO3.4 region will warm over the next six months, but remain within the neutral range. The most recent NINO3.4 value is +0.1 °C for the week ending 15 September 2013.

Indian Ocean Dipole (IOD)

The IOD index has been above −0.4 °C (which is considered the threshold value for a negative IOD event) since early August 2013, with the latest weekly value −0.1 °C. This neutral period follows on from a negative IOD event which established itself during May 2013. The IOD consensus outlook, from the five surveyed models, indicates these neutral values are likely to persist, meaning that the 2013 negative IOD event has most likely reached its end. However, two models suggest a brief return to negative IOD values. A negative IOD event during winter-spring increases the chances of above normal rainfall over southern Australia.

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 September) predicts NINO3.4 is likely to remain within neutral values throughout the forecast period. The following forecast values 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