Seasonal Climate Outlook August – October 2021

The Bureau of Meteorology (BOM) has released its climate outlook for August to October in Australia. This outlook gives interested parties an insight into what the climate actually has in store for the near future when compared to average temperature and rainfall in Australia.

Key points

  • Rainfall for August to October is expected to be in excess of the median for most parts of Australia.
  • Maximum temperatures for August to October are expected to be in excess of the median in the northern tropics and south-eastern areas of the country.
  • A negative Indian Ocean Dipole has been observed which means that many parts of the eastern Indian Ocean have higher temperatures than normal.
  • The El Niño–Southern Oscillation is neutral, but there is a suggestion that La Niña thresholds could be reached during spring. This would increase the possibility of above average rainfall in eastern and northern Australia.

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Rainfall predictions

Overall, there is a 60% chance that rainfall for most of the country will exceed the median for the time of year. In the eastern part of the mainland, the chances increase to 80%.

The situation is different in Western Australia where parts of the state are expected to have rainfall that is below the median. In southern Victoria and Tasmania there is an equal chance of the rainfall being above or below the median.

There is a strong possibility that these predictions will be correct for most parts of the country as historically they are accurate. However, in parts of Western Australia and south-eastern Australia, previous predictions have been only moderately accurate which means that there is more room for uncertainty.

Temperature predictions

Across the country, nights are expected to be warmer than the median in most areas. The same applies to the days in areas such as the northern tropics and south-eastern Australia. Other areas where temperatures are likely to be higher than normal include most of Victoria, the coast of New South Wales, and Tasmania.

However, in south-western areas of Western Australia there is an equal chance of higher than median or lower than median temperatures. The situation changes again in the area from west of the Great Dividing Range in New South Wales to central western parts of the country. Here, temperatures are likely to be lower than the median.

When it comes to maximum and minimum temperatures for Australia, accuracy of BOM predictions is generally very high. The accuracy of these predictions lessens to moderate for maximum temperatures in some southern mainland areas and north-west Australia. For minimum temperatures, it lessens to moderate in north-west Australia.

Influences on the climate

Currently, a negative Indian Ocean Dipole is underway. The majority of models suggest that this pattern is likely to continue into the middle of spring. This makes it more likely that there will be above average rainfall for winter-spring in southern and eastern parts of Australia.

Another factor that is affecting rainfall predictions is the above average temperature of the sea surface north of the Australian mainland.

In addition, the El Niño–Southern Oscillation (ENSO) is neutral right now. The seven models predicting what will happen indicate that it’s likely the central tropical Pacific will cool. Three of the models predict that La Niña thresholds will be reached in spring. This is another pattern that could be contributing to increased rainfall.

There is also much talk about how climate change is having an effect on rainfall and temperature in Australia. Between 1910–2019, Australia’s climate warmed by 1.44 °C. Also, in recent decades, the southern part of the country has experienced a 10-20% reduction in cool season rainfall.

 

BOM predictions take into account the effects of climate change. Its model uses physics of the atmosphere, oceans, ice, and land. It also takes information from satellites and land and water observations. These models and observations are taken into account, along with natural climate influencers, to optimise the accuracy of predictions.

 

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