Climate Model Summary

Climate Model Summary Archive: February 2015

ENSO neutral, though tropical Pacific Ocean likely to remain warm

The tropical Pacific Ocean remains in a neutral ENSO state, with near normal temperatures in the eastern Pacific, although warmer than normal temperatures remain in the western Pacific near the Date Line.

Most of the surveyed models forecast tropical Pacific Ocean sea surface temperatures to be above average, but remaining within the neutral range until at least May. By July, however, six of the eight models suggest a renewed warming, with the NINO3.4 index likely to reach El Niño thresholds. Forecasts spanning February to May (the traditional ENSO transition period) generally have lower accuracy than forecasts made at other times of year, therefore these forecasts should be treated with caution.

The Indian Ocean Dipole (IOD) has little 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 February) indicate the tropical Pacific Ocean is likely to be warmer than average over the coming months, but most models expect NINO3.4 to remain within the neutral range until at least May. One model anticipates a much stronger warming during the coming months with a May value of NINO3.4 well into El Niño territory. Six of the eight models indicate the warming pattern in the central Pacific to be maintained during the southern winter with values reaching El Niño thresholds in July, while a seventh model falls just short of the El Niño threshold. One model maintains neutral conditions throughout the forecast period.

Model forecasts spanning the February to May period tend to have reduced accuracy than at other times of the year. This period is known as the "predictability barrier" as the temperature gradients across the tropical Pacific Ocean naturally weaken at this time of year. Model outlooks for predictions through autumn and beyond should therefore be treated with caution.

The most recent NINO3.4 value is +0.4 °C for the week ending 15 February 2015. NINO3.4 values between –0.8 °C and +0.8 °C typically indicate neutral ENSO conditions.

Indian Ocean Dipole (IOD) outlook

The Indian Ocean Dipole (IOD) is neutral. The IOD does not affect Australian climate from December to April. This is due to the monsoon trough moving southwards over the regions of ocean where the IOD occurs. This alters the wind patterns, and results in negative or positive IOD patterns 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 1 February) predicts NINO3.4 is likely to warm throughout the autumn and winter months with El Niño thresholds likely to be reached by the austral spring. However, POAMA's forecast skill is lower at this time of year than at other times, due to the autumn predictability barrier. 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