Climate Model Summary

Climate Model Summary Archive: June 2015

El Niño likely to strengthen during spring

El Niño remains in the tropical Pacific with model outlooks suggesting more warming is likely. Sea surface temperature (SST) indices across the Pacific all exceed El Niño thresholds, with collective values not seen since the 1997-98 El Niño. Overall, atmospheric indicators of ENSO remain consistent with El Niño, despite a temporary strengthening of the trade winds in recent weeks.

All models indicate SSTs in the central tropical Pacific (NINO3.4) will rise to at least 1.5 °C above average by September with the average of all eight models suggesting a +2.0 °C temperature anomaly. The most recent NINO3.4 value is +1.3 °C for the week ending 14 June 2015. NINO3.4 values above +0.8 °C typically indicate El Niño.

The Indian Ocean Dipole (IOD) can affect Australian climate from May through to the end of spring. Three out of five models that issue IOD forecasts suggest the potential of a positive IOD event developing by late winter, with the other two models maintaining a mostly neutral outlook. Positive IOD events tend to reduce rainfall in southern and central Australia during the winter and spring months, and can exacerbate rainfall deficiencies caused by El Niño.

NINO3.4 outlook

The latest NINO3.4 forecasts (initialised in June) indicate the central tropical Pacific Ocean is likely to continue to warm throughout the winter and spring months. The average of the model forecasts for September is just above +2.0 °C, increasing to +2.3 °C by November. NINO3.4 values of this magnitude have only been observed on a handful of occasions since 1980; during the 1982-83 and 1997-98 El Niño events. Individual model output ranges between +1.6 °C and +2.8 °C for November; all well above the El Niño threshold.

The most recent NINO3.4 value is +1.3 °C for the week ending 14 June 2015. NINO3.4 values above +0.8 °C typically occur during El Niño events.

Indian Ocean Dipole (IOD) outlook

The IOD can affect Australian climate during the months of May to November. Three out of five model outlooks suggest some tendency towards a positive IOD by spring 2015, while the other two tend towards a neutral outlook. A positive IOD typically reduces rainfall in central and southern Australia, and can therefore exacerbate El Niño driven rainfall deficiencies.

The most recent IOD index value is +0.1 °C for the week ending 14 June 2015 following three weeks at +0.4 °C. Sustained IOD index values above +0.4 °C typically indicate a positive IOD event.

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-month forecast each fortnight. The most recent model run (started on 7 June) predicts that NINO3.4 is likely to peak in July but remain above typical El Niño thresholds until at least the end of the forecast period. The following forecast values (at the top of the table) are for POAMA's NINO3.4 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