Tuesday, 3 January 2012 - Annual Climate Summary for Perth - Product code IDCKGC11L0

Perth in 2011: Hottest year on record for Perth Metro

  • Rainfall: Near average to above average.
  • Maximum temperature: Above average; highest on record at several sites.
  • Minimum temperature: Above average; highest on record at several sites.

Details Extremes Records Summaries Important notes the top

Rainfall

Rainfall across the Perth metropolitan during 2011 area was near average for most sites, in stark contrast to 2010, which was one of the driest years on record (see the Perth 2010 annual climate summary). The Perth metropolitan area saw an above average January, but a below average February and autumn, and thus a relatively dry start to the year. However, near average rainfall during winter followed by an above average spring, and some very heavy rainfall during the first two weeks of December saw annual rainfall totals close to normal, with all sites recording between 97% and 113% of their long-term mean. The reduced rainfall that has been seen in the metropolitan area in recent decades has meant however that recording annual totals near the long-term mean has been rare and in fact in 2011, Mundaring and Perth Airport observed their wettest year for 15 years, since 1996.

Perth Metro recorded 860.8 mm in 2011, making it the wettest year since 2005, when 874.8 mm was observed for the entire year. Last year, Perth Metro experienced its 2nd driest year on record with 503.8 mm. Perth Metro's driest year was 466.8 mm in 2006, while the long-term average is 850.0 mm.

Maximum temperature

Mean daily maximum temperatures were very much above average across Perth during 2011, with Perth Metro and a number of other sites observing their warmest year on record.

The year began with very hot conditions throughout the summer months and into autumn. Heatwave conditions (three or more consecutive days of 35 °C or more) were experienced during 1 to 4 January, 27 to 30 January, and 21 to 28 February for most sites. The hot conditions continued throughout much of March (with another heatwave late in the month) and into the first week of April. December also began with a heatwave making it a very hot start to summer 2011/12, and further heatwave conditions occurred after Boxing day between the 27th and 29th. All months of the year saw either close to average or above average mean maximum temperatures, with no months recording significantly below average maxima, and thus a record hot year was observed at several sites.

Perth Metro saw a mean daily maximum temperature of 25.7°C in 2011, breaking the record of 25.3 °C set in 2010. This is a continuation of a very warm three year period. Perth Metro’s four hottest years in 114 years of record have been 2011 (25.7°C), 2010 (25.3 °C), 1978 (25.2 °C), and 2009 (25.0 °C). The hot conditions were due to consistently warm months throughout most of 2011, with five of the twelve months ranking in the top 10 hottest for their respective month - January (equal 7th), February (3rd), March (1st), April (5th), August (2nd) and October (3rd). Only November observed below average daytime temperatures during 2011, and it was the first month to see below average daytime temperatures at Perth Metro since July 2010.

Perth Metro observed 76 hot days (maximum temperature of 32 °C or more) in 2011, breaking the previous record of 66 in 1978. The annual average is 49 hot days. Perth Metro also observed 39 days over 35 °C, which was second highest behind the 45 in 1978. Perth Metro observed just the 1 day over 40 °C in 2011, below the average of 3.4 days and well shy of the record of 9 days in 2007. These statistics highlight that persistant above average temperatures characterised the year in Perth, and the record heat was not associated with particularly extreme temperature events.

Minimum temperature

Mean daily minimum temperatures were very much above average across Perth during 2011, with a number of sites observing their warmest year on record. Rottnest Island recorded an annual mean minimum temperature of 16.7 °C, the highest in its 111 years of record, and 0.6 °C warmer than previous record of 16.1 °C set in 1984.

Similar to maximum temperatures, minimum temperatures throughout the year were consistently near average or above average in the Perth metropolitan area with no month significantly below average. In fact only three months were seen to be near average, and thus 9 months were in the above average range, leading to record warm conditions in terms of annual means.

The second half of February 2011 saw a particularly warm period with nearly all sites in the Perth region observing minimum temperatures over 20 °C from the 14th through to the end of the month. Perth Metro observed 15 consecutive nights with a minimum temperature of 20 °C or more during February 2011 (14th to 28th), which is the longest hot spell of this kind, breaking the record of 13 nights observed in 1985 (17 February to 1 March) and in 1990 (23 February to 7 March).

The coldest night of 2011 for most sites was on 4 July, with several sites registering daily minimum temperatures of 5 °C or lower, and Jandakot Aerodrome recorded the lowest minimum in Perth in 2011 with -0.4 °C.

Perth Metro observed a mean daily minimum temperature of 14.0 °C during 2011, very much above the average of 12.7 °C, and the highest mean minimum recorded at the Mt Lawley observation site since annual records commenced their in 1994.

Sunshine

The annual mean daily sunshine hours recorded at Perth Airport was 8.7 hours, which was near the average of 8.8 hours. Last year, Perth Airport experienced the sunniest year since records commenced in Perth in 1898 with an average of 9.2 hours of sunshine per day.

Notable events

  • Ex-Tropical Cyclone Bianca approached the Perth region on 30 January 2011, however the low had weakened considerably and only light showers and drizzle were reported overnight.
  • A strong pressure gradient over the south of WA caused fresh to strong and gusty easterly winds on 5 and 6 February 2011, with winds easing during the afternoon of the 7th. Sustained winds of 35 to 45 km/h, with gusts of 75 to 85 km/h, were observed in the Perth hills and foothills. The strong winds caused very high to severe fire dangers and significant bushfires at Redhill and Roleystone/Kelmscott destroyed or damaged over 100 homes.
  • Severe thunderstorms developed during the afternoon of 28 February and produced heavy rainfall in northern, eastern, and southern parts of the Perth metropolitan area during the afternoon. Mundaring, in the Perth hills, observed its second highest March daily rainfall on record with the 82.0 mm in the 24 hours to 9am on the 1st. This was also the highest daily rainfall total in the Perth area for 2011.
  • A strong cold front brought heavy rainfall in the late afternoon of 24 June through to the early morning of 25 June, with many sites registering daily rainfall totals in the 50 to 60 mm range. As a result, flash flooding caused some property damage.
  • Rottnest Island received an exceptionally heavy fall from a thunderstorm with daily total of 66.8 mm on 21 July, the third highest July daily rainfall recorded at Rottnest Island.
  • Flash flooding occurred in Fremantle on 22 July and several cold fronts and a low pressure system produced more downpours and windy weather in the last few days of July which resulted in Jarrahdale observing 72.8 mm, the highest daily rainfall total for winter 2011 in the Perth metropolitan area.
  • Very heavy rainfall was observed in early December during separate thunderstorm events on the 6th and 13th, with December daily rainfall records being broken at several sites in the metropolitan area during each of these events. See the Special Climate Statement Very heavy rainfall in southern WA for more information.

Further information

Western Australia Climate Services Centre
Bureau of Meteorology
Phone (08) 9263 2222
Email climate.wa@bom.gov.au
Extremes in 2011
Hottest day 42.0 °C at Gosnells City on 29 Jan
Warmest days on average 26.1 °C at Pearce RAAF
26.1 °C at Perth Airport
Coolest days on average 23.2 °C at Bickley
23.2 °C at Rottnest Island
Coldest day 9.6 °C at Bickley on 11 Jul
Coldest night -0.4 °C at Jandakot Aero on 4 Jul
Coolest nights on average 12.2 °C at Bickley
Warmest nights on average 16.7 °C at Rottnest Island
14.9 °C at Champion Lakes
14.9 °C at Swanbourne
Warmest night 27.5 °C at Medina Research Centre on 28 Jan
Wettest overall 1267.0 mm at Mundaring
Wettest day 82.0 mm at Mundaring on 1 Mar
Highest wind gust 126 km/h at Rottnest Island on 27 Jul

tails Extremes Records Summaries Important notes the top

Highest total annual rainfall for at least 10 years
Total rainfall
for 2011 (mm) 		Most recent annual
this high or higher		 Years since
higher		 Annual
average
Mundaring 1267.0 1277.4 in 1996 15 1074.2
Perth Airport 834.2 889.2 in 1996 15 775.1


Record highest annual mean daily maximum temperature
Mean daily maximum
temperature
for 2011 (°C) 		Previous annual
highest		 Years of
record		 Annual
average
Perth Airport 26.1 26.0 in 2010 66 24.4
Medina Research Centre 25.7 25.5 in 2010 21 24.2
Jandakot Aero 25.8 25.7 in 2010 19 24.4
Perth Metro 25.7 25.3 in 2010 114 24.5
Swanbourne 25.5 24.8 in 2010 17 23.9


Record highest annual mean daily minimum temperature
Mean daily minimum
temperature
for 2011 (°C) 		Previous annual
highest		 Years of
record		 Annual
average
Pearce RAAF 13.8 13.2 in 1967 48 12.2
Medina Research Centre 14.0 12.7 in 2003 21 12.2
Jandakot Aero 12.9 12.7 in 1991 19 11.2
Rottnest Island 16.7 16.1 in 1983 111 15.6
Bickley 12.2 11.4 in 1994 17 11.1
Swanbourne 14.9 14.2 in 2000 17 13.8

Highest annual mean daily minimum temperature for at least 10 years
Mean daily minimum
temperature
for 2011 (°C) 		Most recent annual
this high or higher		 Years since
higher		 Annual
average
Perth Airport 13.6 13.7 in 1963 48 12.1


Details Extremes Records Summaries Important notes the top

Summary statistics for 2011
Maximum temperatures
(°C)		 Minimum temperatures
(°C)		 Rainfall
(millimetres)
Mean
for
2011		 Diff
from
average		 Highest
for
2011		 Mean
for
2011		 Diff
from
average		 Lowest
for
2011		 Total
for
2011		 Average
annual
total		 Rank
of
2011		 Fraction
of annual
average
Bickley 23.2 +0.7 38.1 28 Jan 12.2 +1.1 3.0 5 Aug 1204.6 1079.9 high 112%
Champion Lakes 25.0   39.5 29 Jan 14.9   3.8 4 Jul
Garden Island HSF 23.9   37.9 28 Dec 15.9   7.4 4 Jul 649.6 607.3 average 107%
Jandakot Aero 25.8 +1.4 40.6 29 Jan 12.9 +1.7 -0.4 4 Jul 915.6 831.6 average 110%
Medina Research Centre 25.7 +1.5 40.0 16 Feb 14.0 +1.8 1.3 4 Jul 750.0 762.2 average 98%
Pearce RAAF 26.1 +1.0 41.8 28 Jan 13.8 +1.6 0.7 4 Jul 636.8 658.1 average 97%
Perth Airport 26.1 +1.7 41.8 29 Jan 13.6 +1.5 0.2 4 Jul 834.2 775.1 average 108%
Perth Metro 25.7 +1.2 40.4 29 Jan 14.0 +1.4 1.3 4 Jul 860.8 850.0 average 101%
Rottnest Island 23.2 +1.1 36.3 28 Dec 16.7 +1.1 9.2 3 Jul 712.4 682.7 average 104%
Swanbourne 25.5 +1.6 40.1 28 Dec 14.9 +1.1 4.7 4 Jul 822.6 725.7 high 113%

Details Extremes Records Summaries Important notes the top

Notes

A Annual 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 4 pm on Tuesday 3 January 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

Western Australia Climate Services Centre
Bureau of Meteorology
Phone (08) 9263 2222
Email climate.wa@bom.gov.au