Perth in autumn 2017: Dry with mild temperatures

It was a dry autumn across the Perth metropolitan area with rainfall below average. Mean maximum temperatures were close to average for some sites, but below average for coastal and island sites and above average for parts of the coastal plain. Mean minimum temperatures were close to average.

Below average rainfall

  • Autumn rainfall was only one-half to two-thirds of the long-term average, due to the combination of a wet March, a rain free April, and a below average May
  • Perth Metro recorded a total of 94.4 mm, its lowest autumn rainfall for 8 years, since 57.8 mm in autumn 2009
  • A 38-day dry spell at Perth Metro (28 March-4 May) was its 5th-longest autumn dry spell since records commenced in 1876, and longest for 13 years since a 39-day autumn dry spell between 1 March and 8 April 2004
  • Zero rain in April at Perth Metro was its fourth rain free April on record. Other rain free Aprils occurred in 1982, 1977, and 1920

Cooler daytime temperatures near the coast; Cooler overnight temperatures

  • Mean maximum temperatures were close to normal for some sites, but some coastal plain sites saw mean maxima 0.5-0.6 °C above average
  • Coastal and islands sites were close to 1 °C below average, and Swanbourne and Rottnest Island had their coolest autumn daytime temperatures for over two decades
  • Perth Metro's mean maximum of 25.9 °C equalled its seasonal average, but it was warmer than previous two autumns
  • Mean minimum temperatures were slightly below average for most sites, though Pearce RAAF recorded a mean 1.1 °C below average
  • Perth Metro's mean minimum of 13.4  °C was 0.3 °C below average, and 1.0 °C cooler than last autumn

Further information

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Extremes in autumn 2017
Hottest day 40.1 °C at Pearce RAAF on 1 Mar
Warmest days on average 26.9 °C at Pearce RAAF
Coolest days on average 22.8 °C at Rottnest Island
23.2 °C at Bickley
Coldest day 12.8 °C at Bickley on 20 May
Coldest night 3.8 °C at Pearce RAAF on 28 May
Coolest nights on average 12.1 °C at Bickley
Warmest nights on average 16.7 °C at Rottnest Island
14.7 °C at Swanbourne
Warmest night 24.5 °C at Gosnells City on 4 Mar
Warmest on average overall 19.7 °C at Perth Metro
19.7 °C at Rottnest Island
Coolest on average overall 17.7 °C at Bickley
Wettest overall 143.0 mm at Bickley
143.0 mm at Bungendore
Driest overall 73.4 mm at Perth Airport
Wettest day 32.8 mm at Bickley on 21 May
Strongest wind gust 85 km/h at Rottnest Island on 21 May

Record lowest autumn mean daily maximum temperature
New record
(°C)
Old
record
Years of
record
Average for
autumn
Swanbourne 24.3 = 24.3 in 2016 23 25.5

Lowest autumn mean daily maximum temperature for at least 20 years
Observed
(°C)
Most recent
lower
Average for
autumn
Rottnest Island 22.8 22.2 in 1993 23.6



Record lowest autumn mean temperature
New record
(°C)
Old
record
Years of
record
Average for
autumn
Swanbourne 19.5 = 19.5 in 2006 23 20.3

Lowest autumn mean temperature for at least 20 years
Observed
(°C)
Most recent
lower
Average for
autumn
Rottnest Island 19.7 19.1 in 1993 20.4



Summary statistics for autumn 2017
Maximum temperatures
(°C)
Minimum temperatures
(°C)
Rainfall
(millimetres)
Mean for
autumn
2017
Diff
from
average
Highest for
autumn
2017
Mean for
autumn
2017
Diff
from
average
Lowest for
autumn
2017
Total for
autumn
2017
Average
for
autumn
Rank of
autumn
2017
Fraction of
autumn
average
Bickley 23.2 -0.4 36.6 1 Mar 12.1 -0.4 6.2 29 May 143.0 212.3 low 67%
Garden Island HSF 23.0 -1.1 30.0 2 Apr 15.6 -0.5 10.2 28 May 83.0 131.5 v low 63%
Gosnells City 26.5 0.0 38.6 1 Mar     8.9 30 Apr 87.7 165.4 low 53%
Jandakot Aero 25.6 -0.2 37.1 1 Mar 12.4 0.0 4.1 28 May 108.2 166.1 low 65%
Medina Research Centre 26.2 +0.5 38.0 4 Mar     5.5 29 Apr 91.9 159.0 v low 58%
Pearce RAAF 26.9 +0.6 40.1 1 Mar 12.3 -1.1 3.8 28 May 81.0 136.0 low 60%
Perth Airport 26.2 +0.5 38.1 1 Mar 12.9 -0.2 4.7 28 May 73.4 155.6 v low 47%
Perth Metro 25.9 0.0 37.7 1 Mar 13.4 -0.3 4.9 28 May 94.4 180.8 low 52%
Rottnest Island 22.8 -0.8 30.0 2 Apr 16.7 -0.4 12.2 28 May 83.0 127.7 low 65%
Swanbourne 24.3 -1.2 34.1 1 Mar 14.7 -0.4 7.2 28 May 100.2 154.0 low 65%
Note: Observations for “Perth Metro” are taken from the current site at Mount Lawley (Bureau number 009225).
Comparisons are made against combined data from the current site (which opened in early 1993) and the previous site at Perth Regional Office (009034), which ran from 1876 to early 1992.

Notes

The Seasonal climate summary, generally published on the first working day of each month, lists the main features of the weather in Perth using the most timely and accurate information available on the date of publication; it will generally not be updated. More extensive discussion of significant weather events, along with later information and data that has had greater opportunity for quality control, will be presented in the Monthly Weather Review.

This statement has been prepared based on information available at 10 am on Thursday 1 June 2017. Some checks have been made on the data, but it is possible that results will change as new information becomes available.

In some situations, some or all of the rainfall is in the form of hail or snow. In these cases the totals given are for the water equivalent: the depth of liquid water that results from melting any frozen precipitation. There can be significant 'undercatch' of snow in strong winds, meaning the true precipitation can be higher than that reported.

Averages for individual sites are long-term means based on observations from all available years of record, which vary widely from site to site. They are not shown for sites with less than 10 years of record, as they cannot then be calculated reliably.
The median is sometimes more representative than the mean of long-term average rain.

Observations for “Perth Metro” are taken from the current site at Mount Lawley (Bureau number 009225).
Comparisons are made against combined data from the current site (which opened in early 1993) and the previous site at Perth Regional Office (009034), which ran from 1876 to early 1992.

The Rank indicates how rainfall this time compares with the climate record for the site, based on the decile ranking (very low rainfall is in decile 1, low in decile 2 or 3, average in decile 4 to 7, high in decile 8 or 9 and very high is in decile 10).
The Fraction of average shows how much rain has fallen this time as a percentage of the long-term mean.

Where temperature area averages are mentioned, they are derived from the ACORN-SAT dataset.

Further information

Media
(03) 9669 4057
Enquiries