Perth in Summer 2009-10

A record hot and dry summer

  • Record dry summer for much of the Perth metropolitan area.
  • Highest or equal highest mean maximum temperature on record.
  • Above average mean minimum temperature.

Rainfall

Very dry conditions prevailed throughout the Perth metropolitan area during summer 2009-10 with many sites experiencing their driest summer on record including Perth Metro, Perth Airport and Pearce RAAF, with the latter two registering no rainfall for the entire summer.

Extended dry spells, which began in late spring (21 November 2009), were observed at many stations in the Perth area over summer 2009-10. By 9am on 28 February 2010, Perth Airport had registered 100 continuous days without measurable rain, which was 17 more than its previous longest dry spell of 83 days between 24 December 1947 to 15 March 1948. Perth Metro had 78 days without measurable rainfall until 7 February 2010, when 0.2 mm was recorded, which was Perth Metro's second longest dry spell on record. The longest dry spell at Perth Metro was 83 days between 15 December 1974 and 7 March 1975.

While summer is usually a time of low rainfall in the Perth region, higher than normal pressure over southern WA and a lack of moisture from the tropics due to a generally suppressed monsoon over WA resulted in relatively few thunderstorms over the Perth area in summer 2009-10, and thus a record dry summer for many Perth metropolitan locations.

Perth Metro recorded 0.2 mm on 1 day during summer 2009-10, which is Perth Metro's driest summer since records commenced in 1876. The previous record was in 1974-75 with 0.8 mm on 2 days and the average for summer at Perth Metro is 35.1 mm on about 8 days.

Maximum temperature

Sites across the Perth metropolitan area all experienced their hottest or equal hottest summer on record in terms of mean daily maximum temperature, with the highest departure from mean maximum summer temperature of +2.7°C at Perth Airport.

Several heat waves (three or more days of maximum temperature over 35°C) were observed at several Perth sites during summer 2009-10: 2 to 5 January; 17 to 19 January; and 24 to 28 February. During the second hot spell (17-19 January), Perth Airport recorded three days with daily maximum temperatures above 42C, which had only occurred once before at the airport (18 and 21 January 1961) since records began in 1944. Perth Metro recorded three days with daily maximum temperatures above 41.0C from 17 to 19 January. A run of three days over 41C has happened on only two other occasions at the official Perth site since recording began in 1897: 13 to 15 March 1922 and 7 to 9 February 1933. The hottest temperature for summer 2009-10 was registered during this time with Pearce RAAF recording 44.2°C on 18 January 2010.

Perth Metro's mean daily maximum temperature in summer 2009-10 was 32.0°C, which ranked as equal hottest mean maximum temperature for summer on record with 1977-78. Daily maxima ranged from a mild 22.6°C on 2 December 2009 to a very hot 42.9°C on 17 January 2010, which was Perth Metro's highest daily maximum temperature for January since the current record of 45.8°C on 31 January 1991.

Minimum temperature

Mean daily minimum temperatures during summer 2009-10 were above to very much above average across the Perth metropolitan area, and up to 1.0C warmer than normal at eastern and southern recording sites.

Bickley recorded its highest summer mean daily minimum temperature of 15.6°C, whilst Swanbourne registered its highest daily minimum temperature with 27.2C on 26 February during a heatwave at the end of summer.

Perth Metro's mean minimum temperature for summer 2009-10 was 18.0°C, 0.7°C above average. Daily minima ranged from a hot 26.8°C on 19 January 2010, the highest daily minimum temperature for January since the current record of 27.8°C on 21 January 1989, to a cool 12.3°C on 5 February 2010.

Wind

There were a higher percentage of easterly winds in the Perth hills in the morning during summer 2009-10 and Perth Airport reported 57% of east to southeasterly winds at 9am, compared with the long-term average of 47%.

A highest daily wind gust for summer of 89 km/h was recorded at Rottnest Island on 30 January 2010, when a strong south-southwesterly sea-breeze was experienced in the Perth metropolitan area.

Other Phenomena

The average sunshine hours for summer 2009-10 was 11.6 hours, which was just above the long-term average of 11.4 hours.

Further information

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Extremes in summer 2009-10
Hottest day 44.2 °C at Pearce RAAF on 18 Jan 2010
Warmest days on average 34.4 °C at Pearce RAAF
Coolest days on average 26.6 °C at Rottnest Island
Coldest day 20.3 °C at Garden Island on 16 Dec 2009
Coldest night 7.8 °C at Jandakot Aero on 3 Feb 2010
Coolest nights on average 15.6 °C at Bickley
Warmest nights on average 19.0 °C at Rottnest Island
Warmest night 28.8 °C at Pearce RAAF on 18 Jan 2010
Wettest overall 5.6 mm at Serpentine
Wettest day 4.0 mm at Gosnells City on 24 Jan 2010
Highest wind gust 89 km/h at Rottnest Island on 30 Jan 2010

Record lowest total summer rainfall
Total rainfall
for summer 2009-10 (mm)
Previous lowest
for summer
Years of
record
Average for
summer
Perth Airport 0.0 0.5 in 1974 66 34.0
Pearce RAAF 0.0 0.2 in 1997 55 30.6
Bickley 1.2 3.0 in 2003 39 49.1
Jandakot Aero 0.2 0.5 in 1973 35 42.6
Perth Metro* 0.2 0.8 in 1975 134 35.1
Swanbourne 0.2 0.6 in 1993 17 30.5

Record highest summer mean daily maximum temperature
Mean daily maximum
temperature
for summer 2009-10 (°C)
Previous highest
for summer
Years of
record
Average for
summer
Perth Airport 33.4 32.9 in 1977 65 30.7
Pearce RAAF 34.4 = 34.4 in 1977 47 32.2
Medina Research Centre 31.8 30.8 in 1994 20 29.8
Jandakot Aero 32.9 31.3 in 1997 19 30.3
Gosnells City 34.0 33.2 in 1997 16 31.9
Swanbourne 30.7 30.3 in 1999 16 29.0
Bickley 31.8 30.8 in 1997 15 29.6
Perth Metro* 32.0 =32.0 in 1997 113 30.2

Record highest summer daily minimum temperature
Highest daily minimum
temperature
in summer 2009-10 (°C)
Previous highest
for summer
Years of
record
Average for
summer
Swanbourne 27.2 on 26 Feb 2010 27.1 on 26 Feb 1997 17 17.5

Record highest summer mean daily minimum temperature
Mean daily minimum
temperature
for summer 2009-10 (°C)
Previous highest
for summer
Years of
record
Average for
summer
Bickley 15.6 15.5 in 1994 15 14.7

Summary statistics for summer 2009-10
Maximum temperatures
for summer
(°C)
Minimum temperatures
for summer
(°C)
Rainfall
for summer
(millimetres)
Mean for
summer
2009-10
Diff
from
average
Highest for
summer
2009-10
Mean for
summer
2009-10
Diff
from
average
Lowest for
summer
2009-10
Total for
summer
2009-10
Average
for
summer
Rank of
summer
2009-10
Fraction of
summer
average
Bickley 31.8 +2.2 41.8 18 Jan 2010 15.6 +0.9 9.4 2 Dec 2009 1.2 49.1 lowest 2%
Champion Lakes 32.4   41.5 17 Jan 2010 18.6   12.4 2 Dec 2009 0.4
Garden Island HSF 27.5 +1.0 40.4 17 Jan 2010 18.6 +0.5 13.3 8 Dec 2009 1.6 26.0 v low 6%
Gosnells City 34.0 +2.1 43.8 17 Jan 2010 18.6 +1.0 11.5 3 Feb 2010 4.0 38.1 v low 10%
Jandakot Aero 32.9 +2.6 43.0 18 Jan 2010 16.7 +0.8 7.8 3 Feb 2010 0.2 42.6 lowest 0%
Medina Research Centre 31.8 +2.0 43.8 17 Jan 2010 17.4 +1.0 10.7 3 Feb 2010 5.0 41.1 low 12%
Pearce RAAF 34.4 +2.2 44.2 18 Jan 2010 17.1 +0.9 8.9 5 Feb 2010 0 30.6 lowest 0%
Perth Airport 33.4 +2.7 43.2 18 Jan 2010 17.4 +1.0 9.1 2 Dec 2009 0 34.0 lowest 0%
Perth Metro* 32.0 +1.8 42.9 17 Jan 2010 18.0 +0.7 12.3 5 Feb 2010 0.2 35.1 lowest 1%
Rottnest Island 26.6 +0.6 41.1 17 Jan 2010 19.0 +0.5 14.0 8 Dec 2009 3.4 24.5 low 14%
Swanbourne 30.7 +1.7 42.9 17 Jan 2010 18.1 +0.6 12.3 3 Feb 2010 0.2 30.5 lowest 1%

Notes

The Seasonal Climate Summary is prepared to list 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. 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.

This statement has been prepared based on information available at 9 pm on Monday 1 March 2010. Some checks have been made on the data, but it is possible that results will change as new information becomes available.

Averages 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 5 years of record, as they cannot then be calculated reliably.
The median is sometimes more representative than the mean of long-term average rain.

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.

Records in this summary are based on sites with at least 10 years of data.

*Official Perth observations have been recorded at several different sites with varying instrumentation over the years, and these changes can affect the continuity of the climate record. For the current Mt Lawley site, the most significant changes of this kind relate to temperature and rain days.

For that reason, current mean temperature and rain-day data quoted here are based only on readings from the Mt Lawley site, which commenced observations in 1993. Sunshine recordings are from Perth Airport and for similar reasons current means use only Perth Airport data, which commenced in 1993.

For PDF files of Perth Metro monthly climate statistics, please click here for extremes and here for averages.

Further information

Media
(03) 9669 4057
Enquiries