Tuesday, 1 September 2009 - Monthly Climate Summary for Perth - Product Code: IDCKGC11LO

Warm nights and wet cloudy days for Perth in August

Rainfall - near average: The city received 111.0 mm of rainfall over 20 days in August, compared with the average of 134 mm on about 16 days. Historically, August rainfall has ranged from 11.8 mm in 1902 to 318.3 mm in 1945. The wettest day in August 2009 was the 21st when 16.2 mm was recorded.

Wet spell - the longest in 13 years:  Between the 8th and 24th August, Perth recorded 17 consecutive rain days, which was its longest wet spell in Perth for 13 years, since the 23 consecutive rain days from the 16th July to 7th August in 1996.

Year to date rainfall - very much below average: The total rainfall for the 8-month period (January-August) this year was 483.0 mm on 71 days, which was the ninth driest January to August period on record, and the driest since the 340.4 mm on 63 days in 2006. The average for the January to August period is 685 mm on about 77 days. The total rainfall for the same period last year was 624.2 mm on 71 days.

Perth's top 10 driest years to date
(January-August )
Year
Rainfall (mm)
Rain Days
Ranking
2006
340.4
63
1
1940
361.7
65
2
1914
405.6
74
3
1894
437.6
69
4
1979
455.8
75
5
1977
474.4
68
6
1912
479.5
71
7
1877
480.4
83
8
2009
483.0
71
9
1959
483.4
83
10

Mean daily maximum temperature - near average: Perth's mean daily maximum temperature in August was 18.9°C, compared with the average of 18.8°C. Daily maxima ranged from a cold 15.0°C on the 15th, to a warm 21.4°C on the 8th.

January to August mean daily maximum temperature - third highest on record:
Perth's mean daily maximum temperature for the January to August period was 25.1°C, which was the third highest mean daily maximum temperature on record. The average for the January to August period is 24.4°C. The highest mean daily maximum temperature recorded for January to August in Perth was 25.4°C in 1978.

Perth's top 10 mean maximum temperatures
for year to date (January-August)
Year
Mean Maximum Temperatures (°C)
Departure from normal
Ranking
1978
25.4
+1.0
1
1976
25.2
+0.8
2
2009
25.1
+0.7
3
1988
25.0
+0.6
4
1985
24.9
+0.5
5
2008
24.9
+0.5
5
1949
24.7
+0.3
7
1962
24.7
+0.3
7
1972
24.7
+0.3
7
1991
24.7
+0.3
7
1996
24.7
+0.3
7
1999
24.7
+0.3
7

Mean daily minimum temperature - above average: Perth's mean daily minimum temperature in August was 9.3°C, compared with the average of 8.1°C. It was the highest mean minimum temperature since the 9.7°C in 2006. Daily minima ranged from a cold 2.7°C on the 29th to a mild 14.3°C on the 14th.

Mean sunshine hours - well below average: Perth's mean sunshine hours in August was 6.1 hours, which was the least sunniest August in 25 years since the 5.7 hours in 1984. The average August sunshine hours is 7.2 hours. Last August, Perth experienced its sunniest August on record with 8.5 hours.   

August monthly mean temperature and sunshine
Element

2009

Long- term Average

Highest

Year

Lowest

Year Records Commence
Maximum
Temperature (°C)
18.9
18.8
20.3
1902
16.3
1932
1897
Minimum Temperature (°C)
9.3
8.1
11.5
1977/1983
5.6
2008
1897
Sunshine
(hours per day)
6.1
7.2
8.5
2008
4.2
1945
1898
August rainfall and rain days
Element 2009 Long-term Average Highest Year Lowest Year Records Commence
Rainfall (mm)
111.0
  134   
318.3
1945
11.8
1902
1876
Rain days
20
15.7
29
1955
4
1902/1978
1876

August daily extremes
Element 2009 Date Extreme Date

Records Commence

Highest daily maximum (°C)
21.4
08/08/2009
27.8
21/08/1940
1897
Lowest daily maximum (°C)
15.0
15/08/2009
9.9
05/08/1951
1897
Highest daily minimum (°C)
14.3
14/08/2009
17.0
07/08/2006
1897
Lowest daily minimum (°C)
2.7
29/08/2009
1.3
21/08/2000
1897
Wettest 24 hours to 9am (mm)
16.2
21/08/2009
73.9
14/08/1945
1876

Climate of Perth in September

September is the first month of spring. The warming and drying trends accelerate in Perth as monthly rainfall and the number of wet days typically fall, whilst mean maximum and minimum temperatures and the number of sunshine hours increase.

September monthly mean temperatures and sunshine
Element Average Highest Year Lowest Year

Records
Commence

Maximum temperature (°C)
20.1
22.6
1987
16.8
1915
1897
Minimum temperature (°C)
9.5
12.4
1988
8.0
2004
1897

Sunshine (hours per day)

7.7
8.8
4 years
4.9
1907
1898
September monthly rainfall and rain days
Element
Average
Highest
Year
Lowest
Year
Records Commence
Rainfall (mm)
81
199.1
1923
8.7
1916
1876
Rain days
15.2
26
1915
4
1877
1876

September daily extremes
Element
Highest
Date
Lowest
Date
Records Commence
Maximum temperature (°C)
32.7
30/09/1918
11.4
17/09/1917
1897
Minimum temperature (°C)
19.5
08/09/1916
1.0
22/09/2008
1897
Rainfall 24 hours to 9am (mm)
51.8
14/09/1984
n/a
n/a
1876

Warm days in September: On average, Perth can expect two days when the maximum temperature is 25°C or higher. The record is 10 days in 1987, when the highest mean daily maximum temperature on record for September of 22.6°C was recorded.

Earliest 32-degree day of the season (hot day): The earliest 32-degree maximum temperature of the season was on the 18th September 1988, when 32.3°C was recorded, the second highest temperature for September on record.

Cold days in September: On average, Perth can expect approximately one day every five years when the maximum temperature is 15°C or lower. The record is four days in 1903 whilst there was no such day last year.

Cold nights in September: On average, Perth can expect three nights when the minimum is 5°C or lower. The record is seven nights in 2004 and there were three such nights last year.

Note: 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 Perth (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 Perth (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.

Further information:
John Relf (JR) and Glenn Cook Western Australia Climate Services Centre
on, tel: (08) 9263 2222, office hours.