Climate Model Summary

Climate Model Summary Archive: October 2015

El Niño to peak towards end of 2015; rapid decay likely in first quarter of 2016

El Niño continues to strengthen with sea surface temperatures in the central tropical Pacific approaching peak values observed during the strong 1997-98 El Niño. Model outlooks, as well as all atmospheric and oceanic indicators, indicate further intensification is likely.

Temperatures in the NINO3.4 area of the central tropical Pacific are now 2.2 °C warmer than average. The all-model average forecast suggests this area could warm to 2.8 °C above average in November and December - equalling and exceeding peak values of the 1982-83 and 1997-98 El Niños respectively - before weakening in early 2016.

The Indian Ocean Dipole (IOD) is positive. Positive IOD events tend to reduce rainfall in southern and central Australia during the winter and spring months, exacerbating rainfall deficiencies caused by El Niño. Model outlooks indicate the positive IOD will decay by the end of spring.

While El Niño and the IOD are strong influences on Australian climate at certain times of year, other factors may also influence climate outlooks—see the Climate Outlooks page for the latest rainfall and temperature outlooks.

NINO3.4 outlook

The latest NINO3.4 forecasts (initialised in October) indicate that sea surface temperatures across the central tropical Pacific Ocean are likely to peak in November or December, followed by a rapid weakening heading into autumn 2016. The all-model average NINO3.4 outlook for November is +2.8 °C, but drops to +1.8 °C by March. Individual model values range between +2.5 °C and +3.0 °C for November; all well above the El Niño threshold and indicative of a substantial El Niño.

The most recent NINO3.4 value is +2.2 °C for the week ending 11 October 2015. NINO3.4 values above +0.8 °C typically occur during El Niño events.

Indian Ocean Dipole (IOD) outlook

The Indian Ocean Dipole (IOD) is positive; the index having been at or above the positive IOD threshold (+0.4 °C) for ten consecutive weeks. The most recent weekly index value is +1.2 °C (11 October 2015) which is the highest value of the IOD index since the positive event of 2006.

A positive IOD typically reduces winter–spring rainfall in central and southern Australia, and can therefore exacerbate El Niño driven rainfall deficiencies. The effect of both the 2015 El Niño and positive IOD (as well as cool waters to the north of Australia, typical of El Niño) is already apparent in the drier-than-average September 2015 and October-to-date rainfall patterns across Australia.

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 11 October) suggests the central tropical Pacific Ocean will continue to warm, peaking towards the end of the year at values close to, or just exceeding, the peak NINO3.4 value of the 1997-98 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