Climate Model Summary Archive: July 2015

El Niño likely to strengthen and persist through 2015

El Niño remains well established in the tropical Pacific. All models surveyed indicate further warming of the tropical Pacific is likely over the coming months, and that the 2015 El Niño will remain in place for the rest of the year.

Recent and vigorous tropical cyclone activity, including a rare July southern hemisphere cyclone in the western Pacific, has brought about a strong reversal of the Pacific trade winds. This has resulted in enhanced warming of sea surface temperatures (SSTs) across the Pacific. All of the main SST indices have remained above El Niño thresholds for several weeks, with collective values not seen since the strong 1997-98 El Niño. Atmospheric indicators, such as wind, cloud and pressure patterns, also remain consistent with a well-established El Niño.

All models indicate SSTs in the central tropical Pacific (i.e., NINO3.4) will exceed 2 °C above average by October, with an all-model average temperature anomaly of +2.6 °C. The most recent NINO3.4 value is +1.5 °C for the week ending 12 July 2015. Persistent NINO3.4 values above +0.8 °C typically indicate El Niño.

The Indian Ocean Dipole (IOD) is currently neutral. Three out of the five models that issue IOD forecasts suggest development of a positive IOD is likely in coming months. 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.

NINO3.4 outlook

The latest NINO3.4 forecasts (initialised in July) indicate that sea surface temperatures across the central tropical Pacific Ocean are likely to persist at above El Niño thresholds through until the end of 2015. The all-model average NINO3.4 outlook for October is just above +2.6 °C, increasing to +2.7 °C by December. 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 +2.2 °C and +3.4 °C for December; all well above the El Niño threshold and indicative of a substantial El Niño.

The most recent NINO3.4 value is +1.5 °C for the week ending 12 July 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. Three out of five model outlooks suggest some tendency towards a positive IOD by spring 2015, while the other two suggest 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 +0.3 °C for the week ending 12 July 2015 following three weeks of weak-negative values. 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 5 July) predicts that NINO3.4 is likely to remain at least +2 °C above average - well above El Niño thresholds - until at least the end of the year. The following forecast values (at the top of the table) are for POAMA's NINO3.4 ensemble mean.

POAMA archive 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

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.

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.