Australia has experienced a wide range of contrasting weather and climate conditions this year. Nationally, the main story has been one of warmth.
Temperatures have been well-above average for Australia so far during 2017, meaning the year will be the sixth in row above the 1961–1990 average. The annual mean temperature is on track to be one of the ten warmest on record, although it is very unlikely to exceed the national record set in 2013. The year-to-date anomaly for January to October was 0.96 °C warmer than average.
Daytime maximum temperatures in particular have been very warm nationally. The mean maximum temperature for January to October 2017 was 1.34 °C above average. The annual value is likely to be among the five warmest on record.
Minimum temperatures have also been warmer than average, though less so than maxima. For January to October the mean minimum temperature was 0.57 °C above average, and the annual value is likely to finish in the top 20 for 2017 as a whole. The smaller minimum temperature anomaly partly reflects colder than average and dry conditions in southeast Australia during winter associated with clear skies and frosty nights.
The current climate outlook indicates that temperatures are likely to remain warmer than average over most of the country during November and December, suggesting a warm end to the year.
Rainfall has been above average for Australia as a whole for 2017 so far, but with marked regional variation. Above average totals for the year-to-date have been recorded in much of Western Australia away from the west coast, and across most of the Northern Territory. To date, rainfall has been below average in Tasmania, eastern Victoria, much of New South Wales, and inland Queensland.
While rainfall varies locally, this year has continued the pattern of above average rainfall in tropical and northwestern Australia, and below average rainfall across the far south. This pattern has been a pronounced trend over recent decades, and is a result of increasing monsoonal rainfall in the north and reduced cool season rainfall in the south, associated with higher atmospheric pressure across the middle of the country and fewer rain bearing cold fronts and cut-off lows reaching the south.
The year so far
The year began with above average temperatures in eastern Australia during January, but cooler than average maxima in the northwest associated with heavy tropical rainfall. Very wet weather in Western Australia in late January and early February caused flooding and below average temperatures, while a prolonged heatwave affected the eastern mainland and resulted in a much warmer than average end to summer, including widespread record high temperatures in New South Wales.
Autumn was also warmer than average. The most notable weather event was tropical cyclone Debbie which delivered extreme rainfall, flooding and very warm minimum temperatures to Australia's east coast towards the end of March.
The May to September period was unusually dry for southern, and particularly southeastern, Australia, exacerbating rainfall deficiencies in the far west, much of New South Wales and southern and eastern Queensland.
The lack of frontal systems and rainfall across the southern half of Australia in June saw clear skies accompanied by very cold overnight temperatures and frosts. Record low overnight temperatures were experienced over parts of southern inland New South Wales and northern Victoria. It was also the second-driest June on record nationally, and the driest on record for Victoria.
New South Wales and the Murray Darling Basin had their driest September on record. Sydney experienced its driest September since observations began at Observatory Hill in 1858.
As well as being very dry, September also saw some exceptionally warm days with two extreme heat events resulting in new State monthly temperature records for Victoria, New South Wales and Queensland.
After a slow start due to the dry conditions during June, the snow season was one of the best in recent years. Spencers Creek in the New South Wales Snowy Mountains recorded a snow depth of more than two metres in September, the deepest observed since 2000. The lack of a strong El Niño or La Niña signal may have assisted this, as neutral years historically bring the most consistently good snow seasons in Australia.
In northern Australia, the dry season was unusually warm. The mean maximum temperature for northern Australia for May to September was 2.01 °C warmer than average, the warmest on record by almost 0.5 °C. July was an exceptionally warm month; mean maximum temperatures for the month were the warmest on record for Queensland, the Northern Territory and Western Australia.
Heavy rains associated with surface troughs during the first few days of October and around the middle of the month saw daily rainfall records set at some stations around Bundaberg in the Wide Bay and Burnett District, and around Tully on the North Tropical Coast. Some riverine flooding resulted around Bundaberg.
As we move into the significant weather season for Australia, climate models have started to suggest that a weak La Niña may form in the Pacific Ocean. We will be closely monitoring the situation to help emergency services, and others impacted by the potential for above average rainfall, plan for the rest of the year.
How might 2017 end?
With the year coming to an end, we can start making meaningful estimates of how the 2017 Australian temperatures compare to previous years.
For Australia, the year-to-date mean temperature (January–October) is currently running at third-warmest on record (0.96 °C above average), when compared to other annual values for January–December. This is behind 2013 (+1.20 °C) and 2005 (+1.03 °C), and above 2014 (+0.91 °C).
While climate drivers in the Indian and tropical Pacific oceans are currently neutral, sea surface temperatures in the central Pacific have been cooling since mid-winter. Outlooks suggest that La Niña thresholds may be reached or exceeded during November. If a La Niña does occur this year it is likely to be weak and short-lived, as sea surface temperatures in the tropical Pacific are forecast to warm again in early 2018.
Unlike during a typical La Niña, current seasonal forecasts for the rest of the year do not favour widespread above average rainfall. They do suggest a strong tendency towards warmer than average temperatures for northern and southeastern Australia. A shift towards La Niña conditions may also increase the chance of prolonged warm spells in southeast Australia.
Based on this climate outlook and the behaviour of recent years, we expect that the final annual mean temperature is likely to be between 0.8 °C to 1.2 °C above average. It is very likely the year will fall in the ten warmest on record for Australia. However it is highly unlikely that 2017 will set a new record for Australia's warmest year.
What about the globe as a whole?
The global climate has also experienced several extreme weather events during 2017. The Atlantic Basin had a very active hurricane season with 16 major systems, including Harvey, Irma, and Maria, which caused extensive damage to Central America and the east coast of North America.
East Africa is currently recovering from one of its most severe droughts in recent decades, while monsoonal flooding affected millions in south Asia during August and September. Significant fires raged across California, Chile, South Africa, Portugal, Ireland, Greenland, and Canada.
The World Meteorological Organization (WMO) issued its preliminary statement on the climate of 2017 on 6 November. For the globe as a whole, 2017 is likely to be the second or third warmest year on record, continuing the recent pattern of very warm years. Both 2015 and 2016 also broke the pre-2015 record for warmest year. It is however unlikely that 2017 will beat the current record, set in 2016. The exceptional warmth of 2017 has occurred in the absence of El Niño conditions, which contributed to record warm temperatures globally during 2016 and 2015.
The global mean temperature estimate is produced by the WMO using the average of several global climate datasets. The datasets in 2017 will include, for the first time, two estimates of global-mean temperature based on reanalysis data. These are the European Centre for Medium-Range Weather Forecasts (ERA-Interim) reanalysis, and the Japan Meteorological Agency (JRA-55) reanalysis.
Reanalyses are generated by feeding past and very recent observations of surface temperature and other variables into numerical weather models to achieve complete global coverage of atmospheric behaviour. The reanalyses complement the gridded temperature observations that have been used by WMO in the past—namely the UK Met Office Hadley Centre (HadCRUT4), the US National Oceanic and Atmospheric Administration (MLOST), the US Goddard Institute of Space Studies (GISTEMP).