Climate Model Summary

Climate Model Summary Archive: May 2015

Models indicate tropical Pacific to remain well above El Niño thresholds

The tropical Pacific is in the early stages of El Niño, with weekly sea surface temperatures (SSTs) above El Niño levels for the past five weeks. The latest model outlooks suggest warming is likely to continue in the central tropical Pacific, with SSTs predicted to climb well above the El Niño threshold.

The average of the model forecasts for NINO3.4 for October 2015 is +2.4 °C. A monthly value of NINO3.4 this high has only been observed a few times since records began in 1980 (35 years); during the 1982-83 and 1997-98 El Niño events.

The most recent NINO3.4 value is +1.1 °C for the week ending 17 May 2015. NINO3.4 values above +0.8 °C typically indicate El Niño.

The Indian Ocean Dipole (IOD) starts to impact on Australian climate from May through to the end of spring. The latest model outlooks for the IOD index show some tendency towards a positive IOD event by late winter. 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 May) indicate the tropical Pacific Ocean is likely to remain above El Niño thresholds throughout the forecast period. The average of the model forecasts for October is high at +2.4 °C; this value of NINO3.4 has only been observed on a few occasions since 1980; during the 1982-83 and 1997-98 El Niño events. Individual model output ranges between +1.6 and +2.9 for October; all well above the El Niño threshold.

The most recent NINO3.4 value is +1.1 °C for the week ending 17 May 2015. NINO3.4 values above +0.8 °C typically occur during El Niño events.

Indian Ocean Dipole (IOD) outlook

The IOD can impact on Australian climate during the months May to November. Current forecasts suggest a tendency towards a positive IOD by spring 2015. 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 +0.2 °C for the week ending 17 May 2015. 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 10 May) predicts 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