Climate Model Summary Archive: September 2015

El Niño set to persist at strongest values since 1997-98

El Niño continues to strengthen with sea surface temperatures in the central tropical Pacific now at levels not seen since the 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 at +2.0 °C. The all-model average forecast suggests this area could warm to 2.7 °C above average in December before weakening in early 2016.

The Indian Ocean Dipole (IOD) index has been at or above the positive threshold (+0.4 °C) for six weeks. If the index stays at this level for another fortnight, this will be considered a positive IOD event. Most models indicate this is likely. 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.

While El Niño and the IOD are considered to dominate the Australian climate at specific times of year, other factors may have influence on current climate outlooks—see the Climate Outlooks page for the latest rainfall and temperature outlooks.

NINO3.4 outlook

The latest NINO3.4 forecasts (initialised in September) indicate that sea surface temperatures across the central tropical Pacific Ocean are likely to peak towards the end of the year, followed by a rapid weakening heading into autumn 2016. The all-model average NINO3.4 outlook for December is just above +2.7 °C, but drops to +2.1 °C by February. Individual model values range between +2.3 °C and +3.2 °C for December; all well above the El Niño threshold and indicative of a substantial El Niño.

The most recent NINO3.4 value is +2.0 °C for the week ending 13 September 2015. NINO3.4 values above +0.8 °C typically occur during El Niño events.

Indian Ocean Dipole (IOD) outlook

The Indian Ocean Dipole (IOD) index has been above the positive IOD threshold (+0.4 °C) for six weeks; the most recent weekly index value is +0.9 °C (13 September 2015). Should values persist above the threshold for another fortnight, it will be declared a positive IOD event. Four out of five surveyed models indicate this is likely, with forecasts suggesting the IOD index will remain above the positive IOD threshold until at least November. A positive IOD typically reduces winter–spring rainfall in central and southern Australia, and can therefore exacerbate El Niño driven rainfall deficiencies.

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 15 September) 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.

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.

IOD outlook bar-graphs

Past climate model summaries

October 2015 El Niño to peak towards end of 2015; rapid decay likely in first quarter of 2016
September 2015 El Niño set to persist at strongest values since 1997-98
August 2015 Models maintain El Niño into 2016
July 2015 El Niño likely to strengthen and persist through 2015
June 2015 El Niño likely to strengthen during spring.
May 2015 Models indicate tropical Pacific to remain well above El Niño thresholds.
April 2015 Models maintain outlooks for El Niño through winter and spring.
March 2015 Model consensus indicates El Niño by winter 2015.
February 2015 ENSO neutral, though tropical Pacific Ocean likely to remain warm.
January 2015 Models suggesting neutral for now, but remaining warm.
December 2014 Tropical Pacific Ocean likely to remain near El Niño thresholds over summer.
November 2014 Models near El Niño thresholds.
October 2014 Models ease outlooks for El Niño in summer.
September 2014 El Niño remains on hold.
August 2014 Models ease their El Niño outlook for spring.
July 2014 Majority of models still favour spring El Niño.
June 2014 El Niño remains likely for 2014.
May 2014 El Niño remains likely for 2014.
April 2014 Models suggest El Niño likely by mid-winter.
March 2014 An increased chance of El Niño from winter.
February 2014 Models indicate tropical Pacific to warm.
January 2014 Models suggest tropical Pacific likely to warm over coming months.
December 2013 Neutral ENSO through summer.
November 2013 Neutral ENSO through summer.
October 2013 Neutral ENSO for austral summer.
September 2013 ENSO and IOD neutral.
August 2013 ENSO neutral; negative IOD weakening.
July 2013 ENSO remains neutral; negative IOD likely
June 2013 Negative IOD, but ENSO remains neutral.
May 2013 Neutral ENSO, possible negative IOD development.
April 2013 Neutral ENSO conditions expected to persist.
March 2013 ENSO neutral set to continue.
February 2013 Models predict neutral conditions to continue.
19 September 2012 Pacific remains close to El Niño thresholds.
5 September 2012 Borderline El Niño conditions continue.
22 August 2012 El Niño remains likely for 2012.
8 August 2012 Models predict weak El Niño in 2012.
25 July 2012 El Niño remains likely in 2012.
11 July 2012 Models suggest increased risk of El Niño in 2012.
27 June 2012 Models suggest further warming through winter.
13 June 2012 Models suggest further warming through winter.
30 May 2012 Neutral in tropical Pacific, but further warming likely.
16 May 2012 Warming in tropical Pacific set to continue.
2 May 2012 Neutral conditions, but warming in tropical Pacific continues.
18 April 2012 Continued warming in tropical Pacific Ocean.
4 April 2012 La Niña ends; conditions neutral.
26 October 2011 La Niña re-established in the Pacific.
27 April 2011 Models predict neutral conditions by southern hemisphere winter.
30 March 2011 Models predict continued weakening of La Niña conditions.
2 March 2011 Models predict continued weakening of La Niña conditions.
2 February 2011 Models predict La Niña will persist into the southern hemisphere autumn.
18 January 2011 Models predict La Niña event will persist through southern hemisphere summer.
8 November 2010 Models predict La Niña event will persist into first quarter of 2011.
27 October 2010 Models predict La Niña event will persist into at least early 2011.
13 October 2010 Models predict La Niña event likely to continue until at least early 2011.
29 September 2010 Models predict La Niña event to continue through 2010.
15 September 2010 Models predict La Niña conditions to continue: La Niña intensifies in the Pacific.
1 September 2010 Models predict conditions to remain above La Niña thresholds: La Niña strengthens in the Pacific.
18 August 2010 Models predict continued cooling in the tropical Pacific: La Niña conditions persist in the Pacific.
31 May 2010 Models predict neutral conditions to persist over coming months, with the possibility of cool conditions later in the year.
April 2010 Models predict neutral conditions to persist over coming months, with the possibility of cool conditions later in the year.
March 2010 Models predict neutral conditions to return to the Pacific by June 2010.
November 2009 Models predict that El Niño conditions will persist through summer 2009/10.