Climate Model Summary

Climate Model Summary Archive: December 2014

Tropical Pacific Ocean likely to remain near El Niño thresholds over summer

The tropical Pacific Ocean remains warm, with surface temperatures exceeding El Niño thresholds for several weeks now. However atmospheric indicators of El Niño, such as the trade winds, cloudiness and tropical rainfall, are yet to show widespread and sustained patterns consistent with El Niño.

Most of the surveyed models forecast tropical Pacific Ocean sea surface temperatures to remain near, or just above, El Niño thresholds in January. Most models indicate NINO3.4 will peak at its maximum temperature in the coming months and then begin to cool. However, all models predict NINO3.4 will still be on the warm side of neutral in May 2015.

Two models indicate El Niño thresholds will continue to be exceeded in May 2015. Model forecasts spanning the autumn months tend to have reduced accuracy than at other times of the year and should therefore be treated with caution.

The Indian Ocean Dipole (IOD) has no observed impact on Australian climate from December to April due to the natural position of the monsoon trough at this time of year.

NINO3.4 outlook

The latest NINO3.4 forecasts (initialised in December) indicate the tropical Pacific Ocean is likely to be warmer than average over the coming months, with most models suggesting sea surface temperatures (SSTs) will be close to, or above, the El Niño threshold for the remainder of the 2014-15 summer. A transition to El Niño this late in the year would be considered unusual.

Two models suggest SSTs will continue to exceed El Niño thresholds until at least May, however, model forecasts spanning the autumn months tend to have reduced accuracy than at other times of the year and should therefore be treated with caution.

The most recent NINO3.4 value is +0.9 °C for the week ending 14 December 2014. Sustained NINO3.4 values above +0.8 °C can indicate El Niño conditions. NINO3.4 has been above this threshold for five weeks now. In this situation, the atmosphere is yet to show a widespread and consistent El Niño signal.

Indian Ocean Dipole (IOD) outlook

The Indian Ocean Dipole (IOD) is neutral. The IOD does not impact on Australian climate from December to April. This is due to the monsoon trough moving southwards over the regions of ocean where the IOD pattern occurs. This alters the wind patterns, and results in the IOD pattern being unable to form during these months.

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 14 December) predicts NINO3.4 is likely to drop just below El Niño thresholds in January, with a gradual cooling throughout the forecast period although remaining warmer than normal. The following forecast values (at the top of the table) are for POAMA's 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