Australia’s warmest 12-month period on record, again

Australia’s warmest September on record

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Australia’s record for warmest 12-month period has been broken for a second consecutive month. This continues a remarkable sequence of warmer-than-average months for Australia since August 2012.

September 2013 was easily Australia’s warmest September on record. The national average temperature for September was +2.75 °C above the long-term (1961–1990) average, which also sets a record for Australia’s largest positive anomaly for any monthly mean temperature. The previous record of +2.66 °C was set in April 2005.

The mean temperature for Australia, averaged over the 12 months from October 2012 to September 2013, was 1.25 °C above the long-term average. This was also 0.17 °C warmer than any 12-month period prior to 2013.

The previous record, set over September 2012 to August 2013, was +1.11 °C above the long-term average, and the record preceding the current warm spell was +1.08 °C, set between February 2005 and January 2006.

Temperatures for the calendar year to date (January to September) have also been the warmest on record, at 1.31 °C above the long-term average, well above the figure set for January to September 2005 (+1.07 °C). 2005 currently holds the record for Australia’s warmest calendar year.

The past 18 months have been characterised by widespread heat across Australia. The mean temperature has been above average over the entire continent.

October 2012 to September 2013 mean temperature deciles for Australia showing 12-month temperatures were the highest on record for 39% of Australia.

In the past 12-month period a large number of mean temperature records have fallen across Australia including:

• Australia’s warmest month on record (January)
• Australia’s warmest September on record
• Australia’s largest positive monthly anomaly on record (September)
• Australia’s warmest summer on record (December 2012 to February 2013)
• Australia’s warmest January to September period on record
• Australia’s warmest 12-month period on record (broken twice, for the periods ending August and September)
• Indeed, Australia’s warmest period on record for all periods 1 to 18 months long ending September 2013

Two significant daily maximum temperature records were also set this year:

• Australia’s hottest summer day on record (7 January)
• Australia’s warmest winter day on record (31 August)

The periods inclusive of September 2013 have also resulted in numerous State and Territory mean temperature records including:

• Warmest September on record for South Australia, Victoria, New South Wales, Queensland and the Northern Territory
• Largest positive monthly anomaly on record for South Australia and Queensland (September)
• The warmest January to September period on record for South Australia, Victoria, New South Wales and the Northern Territory, and also for Melbourne, Sydney and Adelaide
• The warmest 12-month period on record for South Australia, the Northern Territory, and southern Australia

In addition to these records, and those set during the heat events of January and autumn, many individual stations have set records for early season heat or September record highs.

Generally above-average temperatures have persisted with few breaks since September 2012. The period has been characterised by long periods of warmer-than-average days and a distinct lack of cold weather. Nights have also been warmer than average, but less so than daytime temperatures.

Every calendar month since September 2012 has recorded temperatures at least 0.5 °C above average, with eight of those thirteen months topping 1.0 °C above average including January, April, May, July, August and September of 2013. Widespread record warmth has also been recorded in the oceans around Australia.

Monthly mean temperature anomalies for September 2012 to September 2013.

The Remainder of 2013

The year-to-date temperature anomaly is currently so large that mean temperatures during the remaining three months of 2013 only need to be slightly above average for the year to set a new calendar year record. An anomaly of just +0.24 °C for the remainder of the year (i.e. October to December) will result in 2013 equalling the record held by 2005. Zero anomalies for the last three months of the year will result in 2013 finishing as the second-warmest year on record.

It also remains possible that the 12-month mean temperature record will be equalled or broken again before the end of the year, for the periods ending October, November and/or December.

The Bureau’s latest seasonal outlook indicates that both maximum and minimum temperatures are most likely to be above average over most of Australia. The outlook for warmer-than-average temperatures over the remainder of the year is consistent with the Bureau’s knowledge of background temperature trends, and the well-above-average sea surface temperatures that currently surround Australia. Australian temperatures are now on average more than 1 °C warmer than during the 1950s.

Running means for Australian temperature anomalies for 12-month periods ending September 2013. Vertical grid lines mark 12-month periods commencing January 1920, January 1930, etc.