Climate Model Summary

Climate Model Summary Archive: August 2013

ENSO neutral; negative IOD weakening

Neutral conditions persist in the tropical Pacific. All but one of the international climate models surveyed by the Bureau of Meteorology indicate the continuation of the current neutral state throughout spring and into summer.

In the tropical Indian Ocean, the Indian Ocean Dipole has risen above −0.4 °C for the first time since May 2013. All international models surveyed by the Bureau of Meteorology suggest the current negative event is likely to weaken through the spring months with all but one model showing neutral values by November. A negative IOD event during winter-spring increases the chances of above normal rainfall over southern Australia.

NINO3.4 Outlook

The latest NINO3.4 forecasts (initialised in August) from six of the seven surveyed models indicate neutral ENSO conditions are likely to persist. The UKMO model suggests that a brief period of La Niña-like conditions may form during the next few months, however most models have NINO3.4 values staying close to zero (neither El Niño or La Niña) throughout the forecast period. The most recent NINO3.4 value is −0.2 °C for the week ending 11 August 2013.

Indian Ocean Dipole (IOD)

The IOD index has risen to −0.3 °C for the week ending 11 August 2013, the first value above −0.4 °C (which is considered the threshold value for a negative IOD event) since May 2013. This is also the third consecutive week in which the IOD index has weakened. The IOD consensus outlook, from the five surveyed models, indicates that this negative event will weaken during the spring months with all but one of the international models predicting values in the neutral range by November. 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 August) 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 currently 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