Australia in September 2017

In brief

  • Daytime temperatures exceptionally warm for Australia as a whole, but especially New South Wales, Queensland, and the Top End
  • Significant heat event late in the month; many stations across the eastern mainland set daily temperature records
  • A Special Climate Statement will be released in the next few days, discussing the extreme heat
  • Minimum temperatures somewhat above average overall; above average in the west, South Australia, and parts of Queensland, but below average in Tasmania, the inland southeast, and the northwest
  • September rainfall below to very much below average over much of Australia; lowest on record for the Murray-Darling Basin as a whole
  • Rainfall above average across much of the west of Western Australia and Central Australia, western Tasmania, and the western and southern coast of Victoria

Temperatures

September was a very warm month for Australia, particularly in terms of maximum temperatures (equal fifth-warmest September mean maximum temperature on record, 2.03 °C above average). Maximum temperatures for September were above average for Australia as a whole, with maxima in the highest 10% of historical observations (decile 10) for September across the Top End and east of the Northern Territory, the majority of Queensland and New South Wales, part of central eastern South Australia, and parts of the Kimberley and northern Interior in Western Australia. For Queensland as a whole it was the second-warmest September on record, while New South Wales ranked sixth-warmest. Tasmania was the only State to observe cooler than average days.

An exceptional period of unseasonal warm weather during the last week of the month resulted in many high temperature records being set in Victoria, New South Wales, and Queensland. A sequence during which surface and mid-level troughs deepened in the central Australia between slow-moving high pressure systems over the Tasman Sea and low pressure systems to the south of Australia; the result was a strong flow of warm air from central and northern Australia being drawn into eastern Australia, culminating in two distinct pulses of heat.

Many long-term stations set records for early season or monthly high maximum temperature records on the 23rd, 24th and between the 27th and end of the month. Numerous stations in New South Wales, and a few in Queensland, also set records for high overnight minimum temperatures. Some stations set new State records during the first period, which were then broken during the second pulse of hot weather. Multiple area-average temperature records were also set, including Australia's warmest September day on record on the 22nd, reaching an area average of 33.50 °C, more than six degrees above mean (surpassing the previous record of 33.39 °C, set on 30 September 1998).

State records for warmest September day were broken in each of the mainland eastern States: the new records are 37.7 °C at Mildura, Victoria, on the 23rd; 41.4 °C at Wanaaring Post Office, New South Wales, and 42.8 °C at Birdsville, Queensland, both on the 27th.

A Special Climate Statement will be released in the coming days, and will contain a full summary of records set during the event.

Nationally, minimum temperatures were above average (with an anomaly of +0.46 °C).

Minimum temperatures were above average across the west of Western Australia; most of South Australia except away from the northeast, extending into the eastern Interior of Western Australia; large parts of Queensland, particularly in the southwest, southeast and along the coast of the Cape York Peninsula and southern Gulf; and small pockets in of western New South Wales. Minimum temperatures were cooler than average for the Kimberley in Western Australia, extending through the west of the Northern Territory and the central Alice Springs District. Minima were also below average for Tasmania, an area spanning northern border regions of Victoria, through central to northern New South Wales along the western slopes and plain of the Great Dividing Range.

The passage of strong cold fronts followed by clear skies, light winds and relatively dry air brought some particularly cool nights at some points during the start and middle of the month. Between the 4th and 6th snow was reported settling down to 300 m in parts of Victoria including the Otway, Macedon and Dandenong ranges, and down to 100 to 200 m in the west and far south of Tasmania. Snow again settled to low levels in Tasmania on the 8th and 9th. Some sites in Tasmania and Victoria with relatively short record had their coldest September day on record on the 4th or 5th. In New South Wales a handful of sites observed their lowest September minimum temperature on record on the 1st, 2nd, or 17th.


Areal average temperatures
Maximum Temperature Minimum Temperature Mean Temperature
Rank
(of 108)
Anomaly
(°C)
Comment Rank
(of 108)
Anomaly
(°C)
Comment Rank
(of 108)
Anomaly
(°C)
Comment
Australia = 103 +2.03 equal 5th highest 74 +0.46 = 97 +1.25
Queensland 107 +2.85 2nd highest (record +4.12 °C in 2013) 78 +0.69 102 +1.77 7th highest
New South Wales 103 +2.82 6th highest 67 +0.29 100 +1.56 9th highest
Victoria 79 +0.99 57 −0.05 71 +0.47
Tasmania 21 −0.74 27 −0.64 20 −0.68
South Australia 95 +2.03 89 +0.99 94 +1.51
Western Australia 92 +1.36 85 +0.60 94 +0.98
Northern Territory 96 +2.05 = 51 −0.23 = 75 +0.91

Rank ranges from 1 (lowest) to 108 (highest). A rank marked with ’=‘ indicates the value is tied for that rank. Anomaly is the departure from the long-term (1961–1990) average.


Temperature maps
MeanAnomalyDeciles
Mean
daily
maximum
temperatures
Map of mean daily maximum temperature Map of mean daily maximum temperature anomalies Map of mean daily maximum temperature deciles
Mean
daily
minimum
temperatures
Map of mean daily minimum temperature Map of mean daily minimum temperature anomalies Map of mean daily minimum temperature deciles
Mean
daily
temperatures
Map of mean daily temperature Map of mean daily temperature anomalies Map of mean daily temperature deciles

Rainfall

Rainfall for September was below average for most of Queensland south of the Cape York Peninsula, New South Wales, northern and far eastern Victoria, South Australia south of Lake Eyre and east of Ceduna, and the east coast of Tasmania. Below average rainfall was also observed between the Kimberley and western Queensland, however much of northern Australia away from eastern Queensland is typically seasonally dry at this time of year. A large area of the mainland southeast observed monthly rainfall in the lowest 10% of historical observations (decile 1) for September; this region extended from central to southeastern Queensland, across most of New South Wales, parts of northern Victoria, and northern agricultural and parts of southern pastoral districts of South Australia.

For Australia as a whole rainfall was about two thirds of the usual average for September. For New South Wales and the Murray-Darling Basin as a whole September rainfall was the lowest on record, while for Queensland it was the tenth-driest September on record; records commence in 1900.

Large areas of the west of Western Australia recorded above average September rainfall totals, with an unseasonal rain event at the end of the month resulting in above average monthly totals across Central Australia. A wetter than average September was also observed across coastal Victoria between the extreme southeast of South Australia and South Gippsland, and across the west of Tasmania, while light falls across the Cape York Peninsula and heavier falls on the north tropical coast resulted in above average monthly rainfall for northern Queensland.


Area-average rainfall
Rank
(of 118)
Average
(mm)
Departure
from mean
Comment
Australia 35 10.9 −34%
Queensland 10 1.6 −88% 10th lowest; lowest since 2003
New South Wales 1 4.9 −86% lowest
Victoria 37 47.6 −27%
Tasmania 84 160.6 +16%
South Australia 86 20.7 +21%
Western Australia 82 11.3 +7%
Northern Territory 82 5.3 −25%
Murray-Darling Basin 1 7.1 −79% lowest

Rank ranges from 1 (lowest) to 118 (highest). A rank marked with ’=‘ indicates the value is tied for that rank. Departure from mean is relative to the long-term (1961–1990) average.


Rainfall maps
TotalsPercentagesDeciles
Total
rainfall
Map of total rainfall Map of percentage of normal rain Map of rainfall deciles


Australian weather extremes during September 2017
Hottest day 42.8 °C    at Birdsville (Qld.) on the 27th
Coldest day −3.9 °C    at Mount Hotham (Vic.) on the 4th
Coldest night −9.5 °C    at Perisher Valley AWS (NSW) on the 1st
Warmest night 27.8 °C    at Carters Bore (Qld.) on the 27th
Wettest day 143.0 mm at Babinda Post Office (Qld.) on the 19th


Notes

The Monthly Climate Summary is prepared to list the main features of the weather in Australia using the most timely and accurate information available on the date of publication; it will generally not be updated. Later information, including data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review, usually published in the fourth week of the month.

Climate Summaries are usually published on the first working day of each month.

This statement has been prepared based on information available at 1 pm EST on Monday 2 October 2017. Some checks have been made on the data, but it is possible that results will change as new information becomes available, especially for rainfall where much more data becomes available as returns are received from volunteers.

Long-term averages in this statement and associated tables are for the period 1961 to 1990 unless otherwise specified.

The system used for calculating areal averages of rainfall was changed in October 2009; the main effect was that current and historical values for Tasmania were increased. Since October 2012, ACORN-SAT has been used for calculating areal averages of temperature; the major change from earlier datasets is that the ACORN-SAT dataset commences in 1910, and hence rankings are calculated using a larger set of years.


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