Wednesday, 2 January 2013 - Annual Climate Summary for Perth - Product code IDCKGC11L0

Perth in 2012: One of the hottest years on record

• Rainfall: near average to below average
• Maximum temperature: very much above average, one of the hottest years for a number of sites
• Minimum temperature: Above average

Details Extremes Records Summaries Important notes the top

Rainfall

Rainfall across the Perth metropolitan area for 2012 was below average to near average. In general, sites in the Perth Hills and sites near the coast were close to average, while sites on the coastal plain were below to very much below average. Annual totals generally ranged between 500 mm and 700 mm near the coast and on the coastal plain, grading to just over 1000 mm in the hills.

The year of 2012 saw a close to average January and February in the Perth region followed by a dry autumn and very dry winter, which including the driest July on record at most sites. This was followed by above average rainfall during spring, with some record high monthly totals reported in November, and a very much above average December. Slow moving thunderstorms brought significant rainfall to the Perth metropolitan area in the evening of 19 January through to the morning of the 20th, and Chidlow recorded 86.4 mm, the highest daily fall in the Perth region during 2012.

Perth Metro recorded 608.2 mm in 2012, which is very much below the long-term average of 850.0 mm, and ranks as the 12th driest year since records commenced in 1876. The wettest month was June with 140.8 mm, and the driest month was March when 0.2 mm. Most notably, Perth Metro recorded only 34.6 mm in July, its lowest July total rainfall in 137 years of recording. Last year Perth Metro received slightly above average rainfall with 860.8 mm, while Perth Metro's driest year was in 2006 when 466.8 mm was observed.

Maximum temperature

Annual maximum temperatures were generally above average across the Perth metropolitan area during 2012, with means close to 23 °C on the offshore islands and in the hills, and between 25 °C and 26 °C on the coastal plain. Apart from the hills, mean annual maximum temperatures were close to 1.0 °C above average and most sites observed one of their hottest years on record; Perth Metro observed its equal hottest year in 116 years of record with 2011, whilst Perth Airport recorded its third hottest year in 68 years of record, with 2011 being the hottest, and 2010 being the second hottest.

Almost all months in 2012 were warmer than normal across Perth, with the exception of near average maximum temperatures in February and November. The year began with very hot conditions in January and heatwaves (three or more consecutive days with maximum temperatures of 35 °C or higher) were experienced from the 11th to 13th, 18th to 21st, and 24th to 28th for many sites. The daily maximum temperature of 43.1 °C at Swanbourne on the 26th was the hottest day at that site for any month in its 20 years of record, and the hottest day in the Perth metropolitan area during 2012. Heatwaves were also experienced during February from the 8th to 10th, and 20th to 22nd; and twice during March between from the 4th to 6th, and 9th to 12th. A prolonged heatwave of seven consecutive days of over 37 °C was registered at the end of year between the 25 and 31 December for most sites. The seven consecutive days of maximum temperature of 37 °C or higher between 25 and 31 December 2012 at Perth Metro has only been matched on two previous occasions (31 December to 6 January 1962 and 15 to 21 February 1988).

Perth Metro recorded seven heatwaves (three or more consecutive days with maximum temperatures of 35 °C or higher) during 2012, the second highest number recorded in any one year behind the nine in 1978. The two heatwaves in March 2012 were of note as March had seen two heatwaves on only one other occasion (1988) since records began in 1897.

Perth Metro recorded a very warm day on the first day of October, with a maximum temperature of 34.3 °C. This was the earliest instance of a temperature at 34 °C or higher in spring since records commenced in 1897, with the previous earliest date being 12 October. A maximum of 34.1 °C was recorded on 12 October 1968 and 34.0 °C on 12 October 1991.

One of the coldest days of the year in the metropolitan area occurred on 27 September as a result of a burst of cold air over the region after the passage of a cold front. Most sites reported maximum temperatures close to 15 °C; however, in the hills, Bickley reported a maximum of 10.9 °C, the lowest maximum temperature reported in the Perth metropolitan area during 2012.

Perth Metro saw a mean daily maximum temperature of 25.7 °C in 2012, the equal hottest year in 116 years of record. Of the five hottest years in Perth Metro's 116 year recording history, four have occurred in the past four years, the rank order being 2012 (25.7 °C), 2011 (25.7 °C), 2010 (25.3 °C), 1978 (25.2 °C), and 2009 (25.0 °C). During 2012, eight individual months ranked in the top 10 hottest for their respective month for Perth Metro - January (2nd), March (3rd), May (equal 7th), July (3rd), August (equal 4th), September (equal 6th), and October (2nd) and December (3rd).

Minimum temperature

Mean daily minimum temperatures were above average across Perth during 2012, with departures from the long-term mean generally about 0.5 °C. Annual mean minima ranged from 15°C to 16 °C on the offshore islands grading to generally 12 °C to 14 °C on the coastal plain and in the hills.

Monthly mean minimum temperatures were near average in the Perth metropolitan area for much of 2012, aside from January when record high monthly values were observed, and in June, October and December when above average minima were recorded; and in July which saw record low monthly means as a result of the lack of cloud and westerly winds that coincided with Perth Metro's driest July on record. The daily minimum temperature of 25.9 °C at Garden Island on 28 January, during a spell of very warm overnight temperatures in Perth, was the highest overnight temperature for the site for any month since records commenced in 2001. Gosnells City recorded the warmest night in Perth in 2012 during the very warm spell in late January with a minimum of 29.0 °C on the 28th. The coolest night of the year for most sites in Perth was 25 July. Several sites recorded sub-zero minima and Jandakot Aerodrome registered the lowest minimum in Perth for 2012 with –1.6 °C.

Perth Metro observed an annual mean daily minimum temperature of 13.2 °C during 2012, above the average of 12.7 °C. Perth Metro's warmest month, in terms of overnight temperatures, was January, with a mean minimum of 20.1 °C, Perth Metro's equal fifth warmest January, and warmest for 20 years, whilst the coldest month was July with a mean minimum of 5.2 °C, Perth Metro's lowest mean minimum for any month since records commenced at the current Mt Lawley site in 1993.

Sunshine

The annual mean daily sunshine hours recorded at Perth Airport was 8.9 hours, which was near the average of 8.8 hours.

Notable events

• After a length dry period in January 2012, a surface trough off the west coast produced slow moving thunderstorms bringing significant rainfall to the Perth metropolitan area in the evening of 19 January through to the morning of the 20th. Rainfall totals during the event were generally between 10 mm and 70 mm; however, Chidlow recorded 86.4 mm, the highest daily fall in the Perth area during 2012. 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 recorded its wettest January in 86 years of record.
• Significant cold fronts and low pressure systems moved through the Perth region during the early to middle part of June 2012, resulting in a tornado in the suburbs of Dianella and Morley, record high tides at Fremantle Harbour, and wind gusts in excess of 100 km/h. Rottnest Island recorded the highest wind gust of 2012 in the Perth Metropolitan area on 10 June with 119 km/h. Please refer to Special Climate Statement 40 for more details.
• Due to persistent high pressure systems over southern WA and a contraction of cold fronts and westerly flow southwards during July, monthly rainfall totals across the Perth metropolitan area were lowest on record at almost all sites. Rainfall totals in the region were in the 20 to 50 mm range, more than 100 mm less than the long-term average at most sites, and significantly below the previous July records. This event was particularly notable given that some sites have over 100 years of record (Perth Metro 136 years, Jarrahdale 128 years, and Mundaring 111 years), and the low monthly rainfall easily exceeded their previous lowest July total.
• A line of thunderstorms developed over central parts of Perth at approximately 1100 WST on 24 November and moved southward through southern suburbs before thunderstorms to the north of Perth moved over the city in the late afternoon, with heavy falls in the northern and eastern suburbs and hail observed in northern suburbs. The daily total at Perth Airport of 26.0 mm in the 24 hours to 9am on the 25th was the third wettest day in November on record at the site, and 20.8 mm of this total fell in the 10 minutes from 1813 WST to 1822 WST on the 24th, which is a one in 20 to 50 year event.
• A cold front moved across the Perth area early on 28 November, followed by a secondary front during the evening, connected to a rapidly deepening low just off the the WA southwest coast. The systems brought widespread squally showers, very strong winds, and very high tides. Well exposed sites across the metropolitan area recorded maximum wind gusts in excess of 90 km/h, whilst coastal sites recorded wind gusts greater than 100 km/h, with the maximum gust reported during the event being 117 km/h at Rottnest Island. Most wind recording sites in the metropolitan area recorded their greatest November wind gusts for more than 10 years, and Perth Airport recorded its highest November wind gust since 1965. It was a rare occurrence for such a strong storm in late spring and the storm caused traffic congestion, with one lane closed on the Kwinana Freeway due to waves on the Swan River over-topping the sea wall, airport delays, and extensive power outages with reports of 50,000 houses losing power. Daily falls on the 28th and 29th were generally moderate with heavier falls in the Perth hills. Bickley recorded 40.4 mm on the 29th.
• Heavy rainfall was observed at some sites in the metropolitan area due to a middle level low pressure system near the west coast, with Champion lakes observing 50.6 mm in the 24 hours to 9am on 13 December.

Further information

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

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Extremes in 2012
Hottest day	43.1 °C at Swanbourne on 26 Jan
Warmest days on average	26.2 °C at Pearce RAAF
Coolest days on average	22.7 °C at Bickley
Coldest day	10.9 °C at Bickley on 27 Sep
Coldest night	-1.6 °C at Jandakot Aero on 25 Jul
Coolest nights on average	11.7 °C at Bickley
Warmest nights on average	16.3 °C at Rottnest Island 14.2 °C at Swanbourne
Warmest night	29.0 °C at Gosnells City on 28 Jan
Wettest overall	1063.6 mm at Bickley
Wettest day	86.4 mm at Childlow on 20 Jan
Highest wind gust	119 km/h at Rottnest Island on 10 Jun

Extremes Records Summaries Important notes the top

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Record highest temperature
	Highest temperature in 2012 (°C)		Previous annual warmest		Years of record	Annual average
Swanbourne	43.1	on 26 Jan	43.0	on 26 Dec 2007	20	24.0

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Record highest annual mean daily maximum temperature
	Mean daily maximum temperature for 2012 (°C)	Previous annual warmest		Years of record	Annual average
Perth Metro	25.7	= 25.7	in 2011	116	24.6

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Record highest daily minimum temperature
	Highest daily minimum temperature in 2012 (°C)		Previous annual warmest		Years of record	Annual average
Garden Island HSF	25.9	on 28 Jan	25.5	on 12 Mar 2010	12	14.8

Extremes Records Summaries Important notes the top

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Summary statistics for 2012
	Maximum temperatures (°C)				Minimum temperatures (°C)				Rainfall (millimetres)
	Mean for 2012	Diff from average	Highest for 2012		Mean for 2012	Diff from average	Lowest for 2012		Total for 2012	Average annual total	Rank of 2012	Fraction of annual average
Bickley	22.7	+0.2	38.6	31 Dec	11.7	+0.6	2.9	9 Jul	1063.6	1079.5	average	99%
Champion Lakes	24.8		40.8	31 Dec	14.1		2.7	25 Jul	711.0
Garden Island HSF	23.3	+0.7	40.2	25 Jan	15.2	+0.4	5.6	13 Jul	590.6	605.8	average	97%
Jandakot Aero	25.3	+0.8	41.5	26 Jan	11.8	+0.5	-1.6	25 Jul	684.4	827.4	low	83%
Pearce RAAF	26.2	+1.1	42.7	31 Dec	12.5	+0.3	-0.8	25 Jul	544.5	655.5	low	83%
Perth Airport	25.7	+1.3	42.2	31 Dec	12.6	+0.5	-0.7	25 Jul	647.4	773.2	low	84%
Perth Metro*	25.7	+1.1	42.1	31 Dec	13.2	+0.5	0.4	25 Jul	608.2	850.0	low	72%
Rottnest Island	23.2	+1.1	39.5	25 Jan	16.3	+0.7	8.9	28 Sep	493.6	682.7	low	72%
Swanbourne	25.3	+1.3	43.1	26 Jan	14.3	+0.5	3.9	25 Jul	694.8	724.1	average	96%

Extremes Records Summaries Important notes the top

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Further information

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

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