Climate Model Summary

Climate Model Summary Archive: August 2015

Models maintain El Niño into 2016

El Niño is well established in the tropical Pacific and continues to strengthen. All models surveyed indicate further warming of the tropical Pacific is likely over the coming months, with the event likely to peak towards the end of the year.

Temperatures in the NINO3.4 area of the central tropical Pacific are now at levels last recorded during the peak of the 2002-03 El Niño (latest weekly values is +1.8 °C). The all-model average forecast suggests this area could warm to at least 2.8 °C above average by November.

Despite a recent rise in the IOD index, the Indian Ocean Dipole (IOD) remains neutral. Three out of the five models that issue IOD forecasts suggest development of a positive IOD event by September. Two models maintain a 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.

However, the IOD and El Niño are not the only influences on Australian climate—see the Climate Outlooks page for the latest rainfall and temperature outlooks.

NINO3.4 outlook

The latest NINO3.4 forecasts (initialised in August) indicate that sea surface temperatures across the central tropical Pacific Ocean are likely to persist above El Niño thresholds through until at least early 2016. The all-model average NINO3.4 outlook for November is just above +2.8 °C, but drops to +2.5 °C by January. Since the start of the satellite era of ocean observations in the late 1970's, NINO3.4 values this large have only been observed during the 1982-83 and 1997-98 El Niño events. Individual model values range between +2.4 °C and +3.5 °C for November; all well above the El Niño threshold and indicative of a substantial El Niño.

The most recent NINO3.4 value is +1.8 °C for the week ending 16 August 2015. NINO3.4 values above +0.8 °C typically occur during El Niño events.

Indian Ocean Dipole (IOD) outlook

The Indian Ocean Dipole is currently neutral although the IOD index has risen rapidly during August. Three out of five model outlooks suggest some tendency towards a positive IOD during early spring while the other two suggest a neutral outlook throughout the forecast period. 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 +0.4 °C for the week ending 16 August 2015 following a rapid rise in the first week of August. 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 2 August) has strengthened the forecast warming in the central Pacific Ocean with NINO3.4 now likely to reach +2.5 °C above average by November - well above El Niño thresholds and the highest value since the 1997 El Niño. 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