Perth in summer 2011/12: A wet and warm summer

This statement was prepared before all data for the period were available. This may affect some of the statistics presented.
  • Rainfall: Very much above average; highest on record at some sites
  • Maximum temperature: Above average
  • Minimum temperature: Very much above average; highest on record at some sites

Rainfall

Rainfall across the Perth metropolitan area during summer 2011 was very much above average, with most sites recording more than double their normal summer rainfall. The wet summer was primarily due to heavy rainfall events during the first two weeks of December, slow moving thunderstorms in late January, and the passage of ex-Tropical Cyclone Iggy during early February. Pearce RAAF and Garden Island observed their wettest summer on record, while a number of other sites saw their wettest summer in over 10 years.

Significant rainfall events during summer 2011/12 in Perth:

  • A deep middle level trough near the west coast produced significant rainfall and thunderstorms across the Perth metropolitan area on 6 December 2011 and showers continued in the southeastern suburbs on the 7th. Rainfall totals during the event were generally in the 20 mm to 40 mm range, though heavier falls were recorded at Roleystone and Pearce RAAF. The daily rainfall total of 48.8 mm recorded at Pearce RAAF in the 24 hours to 9am on the 7th was its wettest December day in 48 years of record, as well as the wettest day of December 2011 in the Perth area.
  • Another deep mid-level trough near the WA west coast brought further heavy rain and thunderstorms across the Perth metropolitan area in the evening of 12 December 2011 and early on the 13th. Several sites, including Perth Airport, experienced their wettest December day on record. Most of the rain fell due to a slow moving storm in the hours just prior to midnight on the 12th, with Perth Metro recording 36.6 mm in 30 minutes (between 2202 WST and 2231 WST), which is a one in 50 to a one in 100 year event. The daily total of 43.6 mm at Perth Metro in the 24 hours to 9am on the 13th was its third wettest December day since records commenced in 1876.
  • Overnight thunderstorms on 3 January 2012 produced generally light rainfall across the Perth metropolitan area, with daily falls of less than 10 mm registered at most sites on the 4th. This was the first rainfall in Perth for three weeks since the heavy rainfall on 13 December 2011. Further light showers occurred in the eastern suburbs and hills in the evening of the 5th and in the morning of the 6th, with daily totals less than 5 mm. After a lengthy dry period, a surface trough off the west coast produced slow moving thunderstorms and significant rainfall across the Perth metropolitan area in the evening of 19 January and during the morning of the 20th. Rainfall totals during the event were generally in the 10 mm to 30 mm range, with some heavier falls of between 60 and 70 mm observed in the hills and to the southeast. As a result, Jarrahdale, Mundaring, and Chidlow registered their wettest January day in more than 100 years of rainfall record. Serpentine also witnessed its highest daily rainfall for January, and as a result of this single event also recorded its wettest January in 86 years of record.
  • After a very hot Australia day where temperatures reached the low 40s, thunderstorms brought some relief with rain recorded at most sites in the Perth metropolitan area in the afternoon and evening, although falls were generally less than 5 mm.
  • The passage of ex-TC Iggy brought a cloudband and moderate rainfall late on the 2nd and on the 3rd, with totals of generally 10 mm to 25 mm recorded during the event.

Perth Metro recorded 118.2 mm on 11 rain days during summer 2011/12, which was its 5th wettest summer on record, and the wettest summer for 12 years, since 146.2 mm was recorded on 13 rain days in 1999/2000. Rainfall recording commenced at Perth Metro in 1876. The average for summer at Perth Metro is 35.4 mm on 8.2 rain days. Rainfall totals at Perth Metro for individual months this summer were: December 75.8 mm (average 13.3 mm), January 18.8 mm (average 9.6 mm), February 23.6 mm (average 12.6 mm). The wettest day during the summer of 2011/12 was 13 December 2011 when 43.6 mm was recorded, which was the 3rd wettest day at Perth Metro in December on record. Last summer (2010/11), Perth Metro recorded 48.0 mm on 12 rain days.

Maximum temperature

Mean daily maximum temperatures were above to very much above average average for most sites during summer 2011/12, with mean maxima typically 1 to 2 °C above normal. Swanbourne observed its hottest day in 19 years of record with 43.1 °C on 26 January when Perth was in the midst of a heatwave.

Summer 2011/12 began with high daytime temperatures in the first few days of December 2011, with some sites observing heatwave conditions (3 or more consecutive days of daily maximum temperature of 35 °C or higher), before a cool change moved in on the 6th and most sites observed their coolest day for summer 2011/12 on 6 December 2011. Hot conditions returned late in December, with heatwave conditions at most locations from 27 to 29 December, before cooler conditions, in conjunction with some light rainfall, were evident during early 2012. Hot weather returned between the 11th and 13th with another heatwave, mostly confined to the southeast and western suburbs, whilst a 4-day heatwave was observed at Perth Metro, Perth Airport, and Jandakot Aerodrome between the 18th and the 21st. The hottest spell for summer 2011/12 effected the city from 24 to 28 January, with daily maxima in the 35 to 43 °C range and all sites recording their hottest summer 2011/12 day during this period. Some sites recorded a six day heatwave before cooler air from the southeast extended across the city and brought temperatures down to the low 30s in the last two days of January . Hot days returned to Perth for 1 February but the passage of ex-TC Iggy across the Southwest Land Division saw cool conditions across Perth from 2 to 6 February. The cool weather was short lived as another heatwave was experienced at most sites between 8 and 10 February, and again between 20 and 22 February, before summer 2011/12 ended with some cooler weather.

Perth Metro's mean daily maximum temperature for summer 2011/12 was 31.7 °C, 1.3 °C above the summer average of 30.4 °C, and the 4th warmest summer since records commenced in 1897. Daily maxima across summer 2011/12 ranged from a mild 23.9°C on 13 December 2011 to a very hot 42.1 °C on the 28 January 2012, which was the hottest January day at Perth Metro in 2 years since 42.7 °C was recorded on 18 January 2010. Last summer (2010/11), Perth Metro observed a mean daily maximum temperature of 32.0 °C, which was the equal hottest on record with 2009/10 and 1977/78. Perth Metro observed 2 heatwaves in each of the summer 2011/12 months (the first occasion this has occurred), for a record equalling 6 summer heatwaves. The summer of 1977/78 also recorded 6 heatwaves, but also saw another heatwave during March. During summer 2011/12, Perth Metro recorded 4 days with a maximum temperature of 40 °C or higher, which was the greatest number of such days in summer since the 4 days in 2009/10. The average for summer is 3 days, whilst the greatest number of such days is 6 days in 1949/50, 1961/62 and 1997/98.

Minimum temperature

Mean daily minimum temperatures during summer 2011/12 were above to very much above average across the Perth region, with overnight minima more than 1 °C above normal, and at some sites over 2 °C above normal. Several sites equalled or broke their warmest summer on record in terms of overnight temperatures, with warm nights experienced throughout much of December, the second half of January, and in the early and middle parts of February. Very warm nights were observed during the most significant heatwave of the summer from 25 to 28 January, with most sites observing overnight temperatures in the mid-to-high twenties. Swanbourne and Garden Island observed their warmest night on record on the 28th whilst Gosnells City observed the warmest night for summer 2011/12 in the Perth metropolitan area with 29.0 °C on the 28th.

Perth Metro's mean daily minimum temperature for summer 2011/12 was 19.1 °C, and ranks equal 5th warmest on record with 1972/73 and 1975/76. Summer 2011/12 was also the warmest since a mean of 19.2 °C was observed in 1991/92. Daily minima across summer ranged from a mild 12.1 °C on 26 February to a hot 26.6 °C on 28 January. The summer average minimum temperature at Perth Metro is 17.4 °C.

Wind and Sunshine

Perth’s average daily summer sunshine was 10.6 hours, and thus 2011/12 was the least sunniest summer since a mean of 10.6 hours was recorded in summer 2005/06. The average for summer in Perth is 11.4 hours of sunshine per day.

Further information

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Extremes in summer 2011-12
Hottest day 43.1 °C at Swanbourne on 26 Jan 2012
Warmest days on average 32.3 °C at Pearce RAAF
Coolest days on average 27.8 °C at Rottnest Island
Coldest day 20.3 °C at Bickley on 6 Dec 2011
Coldest night 8.8 °C at Jandakot Aero on 26 Feb 2012
Coolest nights on average 16.1 °C at Bickley
Warmest nights on average 20.0 °C at Rottnest Island
19.1°C at Perth Metro
Warmest night 29.0 °C at Gosnells City on 28 Jan 2012
Wettest overall 170.8 mm at Mundaring
Wettest day 86.4 mm at Chidlow on 20 Jan 2012
Highest wind gust 98 km/h at Bickley on 30 Jan 2012

Record highest total summer rainfall
Total rainfall
for summer 2011-12 (mm)
Previous wettest
for summer
Years of
record
Average for
summer
Pearce RAAF 91.2 86.9 in 1952 46 27.7
Garden Island HSF 73.8 63.2 in 2005 11 30.9

Highest total summer rainfall for at least 10 years
Total rainfall
for summer 2011-12 (mm)
Most recent summer
at least this wet
Years since
wetter
Average for
summer
Serpentine 140.8 204.4 in 1954* 37 34.6
Mundaring 170.8 209.4 in 1989 22 47.8
Medina Research Centre 101.6 274.7 in 1991 20 42.9
Perth Airport 112.6 184.8 in 1991 20 35.6
Jarrahdale 150.6 157.8 in 1991* 16 47.7
Bickley 120.8 145.2 in 1999 12 51.0
Gosnells City 84.6 156.4 in 1999 12 39.1
Perth Metro 118.2 146.2 in 1999 12 34.8
Roleystone 112.0 169.6 in 1999 12 46.0
Swanbourne 92.6 145.6 in 1999 12 34.2

* note: there are gaps in the historical record at this site, so it is possible a higher value has gone unreported.




Record highest summer temperature
Highest temperature
in summer 2011-12 (°C)
Previous warmest
for summer
Years of
record
Average for
summer
Swanbourne 43.1 on 26 Jan 2012 43.0 on 26 Dec 2007 19 29.2




Record highest summer daily minimum temperature
Highest daily minimum
temperature
in summer 2011-12 (°C)
Previous warmest
for summer
Years of
record
Average for
summer
Swanbourne 28.0 on 28 Jan 2012 27.2 on 26 Feb 2010 19 17.6
Garden Island HSF 25.9 on 28 Jan 2012 25.5 on 14 Feb 2008 11 18.3



Record highest summer mean daily minimum temperature
Mean daily minimum
temperature
for summer 2011-12 (°C)
Previous warmest
for summer
Years of
record
Average for
summer
Medina Research Centre 18.7 18.6 in 2010 22 16.5
Swanbourne 19.2 18.9 in 2010 18 17.6
Garden Island HSF 19.7 19.6 in 2010 10 18.3



Summary statistics for summer 2011-12
Maximum temperatures
for summer
(°C)
Minimum temperatures
for summer
(°C)
Rainfall
for summer
(millimetres)
Mean for
summer
2011-12
Diff
from
average
Highest for
summer
2011-12
Mean for
summer
2011-12
Diff
from
average
Lowest for
summer
2011-12
Total for
summer
2011-12
Average
for
summer
Rank of
summer
2011-12
Fraction of
summer
average
Bickley 29.1 -0.7 38.0 26 Jan 2012 16.1 +1.3 9.2 5 Feb 2012 120.8 51.0 v high 237%
Champion Lakes 30.9   40.6 28 Jan 2012 19.2   12.1 8 Jan 2012 99.0
Garden Island HSF 28.6 +1.7 40.2 25 Jan 2012 19.7 +1.4 13.9 5 Feb 2012 73.8 30.9 highest 239%
Jandakot Aero 31.5 +1.0 41.5 26 Jan 2012 18.0 +2.0 8.8 26 Feb 2012 68.4 43.3 high 158%
Medina Research Centre 31.3 +1.3 41.8 26 Jan 2012 18.7 +2.2 10.6 8 Jan 2012 101.6 42.9 v high 237%
Pearce RAAF 32.3 0.0 41.3 26 Jan 2012 18.5 +2.2 10.9 8 Jan 2012 91.2 27.7 highest 329%
Perth Airport 31.8 +1.0 41.5 26 Jan 2012 18.5 +2.1 9.6 26 Feb 2012 112.6 35.6 v high 316%
Perth Metro 31.7 +1.3 42.1 28 Jan 2012 19.1 +1.7 12.1 26 Feb 2012 118.2 35.4 v high 334%
Rottnest Island 27.8 +1.7 39.5 25 Jan 2012 20.0 +1.4 14.6 5 Feb 2012 90.2 27.8 v high 324%
Swanbourne 31.1 +1.9 43.1 26 Jan 2012 19.2 +1.6 13.1 8 Jan 2012 92.6 34.2 v high 271%

Notes

This statement was prepared before all data for the period were available. This may affect some of the statistics presented.

A 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 2 pm on Wednesday 29 February 2012. 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 10 years of record.
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 minimum 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 climate statistics for other months, please click here for extremes and here for averages.

Further information

Media
(03) 9669 4057
Enquiries