Monday, 3 August 2009 - Monthly Climate Summary for Perth - Product Code: IDCKGC11LO

Near average July for Perth

Rainfall - near average: The city received 149.6 mm of rainfall on 16 days in July 2009, compared to the average of 170 mm on about 17 days.  The wettest day in July 2009 was the 19th when 30.6 mm was recorded.  Historically, July rainfall total has ranged from 61.5 mm in 1876, to 425.1 mm in 1958. Last July Perth recorded 179.4 mm on 20 days.

Year to date rainfall - below average: The total rainfall for January to July this year was 372.0 mm recorded on 51 days, which was the driest January to July period since the 215.6 mm in 2006. The average for this period is 551 mm on about 61 days. The total for the same period last year was 596.4 mm on 65 days.

Mean daily maximum temperature - near average: Perth's mean daily maximum temperature in July was 17.8°C, compared with the average of 18.3°C, which was the lowest mean daily maximum temperature for July for 6 years, since the 17.8°C in 2003. Daily maxima ranged from a cold 14.3°C on the 20th, to a warm 21.7°C on the 30th, which was the highest daily maximum temperature for July since the 23.7°C on 18th July 2007.

January to July mean daily maximum temperature - equal second highest on record: Perth's mean daily maximum temperature for the January to July period was 26.0°C. This is the equal second highest mean daily maximum temperature for this period (26.0°C was also observed in 1976) since records commenced in 1897. The highest mean daily maximum temperature recorded for January to July in Perth was 26.1°C in 1978 and the average is 25.2°C.

Perth's top 10 mean maximum temperatures
for year to date (January-July)
Year
Mean Maximum Temperatures (°C)
Departure from normal
Ranking
1978
26.1
+0.9
1
1976
26.0
+0.8
2
2009
26.0
+0.8
2
1988
25.8
+0.6
4
1972
25.7
+0.5
5
1985
25.7
+0.5
5
1996
25.6
+0.4
7
1999
25.6
+0.4
7
2008
25.6
+0.4
7
1949
25.5
+0.3
10
1962
25.5
+0.3
10

Mean daily minimum temperature - near average: Perth's mean daily minimum temperature in July was 7.2°C, compared with the average of 8.0°C, which was the lowest mean daily minimum temperature for July for 3 years, since the 6.5°C in 2006. Daily minima ranged from a cold 1.5°C on the 14th to a mild 13.5°C on the 18th.

Cold nights: Perth recorded 11 cold nights this July with minimum temperatures of 5°C or less. It was the greatest number of such nights since the eleven in July 2004.  On average, Perth can expect eight cold nights in July. In 1998 and 2001, Perth recorded the most number of cold nights for July with 16.

July monthly mean temperature and sunshine
Element

2009

Long- term Average

Highest

Year

Lowest

Year Records Commence
Maximum
Temperature (°C)
17.8
18.3
19.9
1976/1977
15.7
1910
1897
Minimum Temperature (°C)
7.2
8.0
11.4
1921
5.3
1997
1897
Sunshine
(hours per day)
6.3
6.0
7.5
1918
3.2
1926
1898
July rainfall and rain days
Element 2009 Long-term Average Highest Year Lowest Year Records Commence
Rainfall (mm)
149.6
170
425.1
1958
61.5
1876
1876
Rain days
16
17.5
29
1946
6
1918
1876

July daily extremes
Element 2009 Date Extreme Date

Records Commence

Highest daily maximum (°C)
21.7
30/07/2009
26.3
††Twice
1897
Lowest daily maximum (°C)
14.3
20/07/2009
10.5
09/07/1906
1897
Highest daily minimum (°C)
13.5
18/07/2009
16.1
12/07/1898
1897
Lowest daily minimum (°C)
1.5
14/07/2009
0.0
Twice
1897
Wettest 24 hours to 9am (mm)
30.6
19/07/2009
95.0
29/07/1987
1876

†Denotes the lowest minimum temperature for July on record on the following dates: 15 July 1997 and 27 July 1998.

††Denotes the highest maximum temperature for July on record on the following dates: 17 & 18 July 1976.

Climate of Perth in August
August heralds the end of winter and generally shows signs of the forthcoming change in the season. Mean temperatures are generally similar to those in July, but there is a slight reduction in the mean rainfall. Mean sunshine hours increase, with an extra 1 hour per day on average.

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

Records
Commence

Maximum temperature (°C)
18.8
20.3
1902
16.3
1932
1897
Minimum temperature (°C)
8.1
11.5
1977/1983
5.6
2008
1897

Sunshine (hours per day)

7.2
8.5
2008
4.2
1946
1898
August monthly rainfall and rain days
Element
Average
Highest
Year
Lowest
Year
Records Commence
Rainfall (mm)
134
318.3
1945
11.8
1902
1876
Rain days
15.7
29
1955
4
1902/1978
1876

August daily extremes
Element
Highest
Date
Lowest
Date
Records Commence
Maximum temperature (°C)
27.8
21/08/1940
9.9
05/08/1951
1897
Minimum temperature (°C)
17.0
07/08/2006
1.3
21/08/2000
1897
Rainfall 24 hours to 9am (mm)
73.9
14/08/1945
n/a
n/a
1876

Warm days in August: On average, Perth can expect a warm day, when the maximum temperature is 25 degrees or higher, one year in five in August. The greatest number of warm days in August was four in 1914, whilst there were none recorded last year.

Cold days in August: On average, Perth can expect one cold day, when the maximum temperature is 15 degrees or less. The greatest number of such days was 10 in 1917. There were none last August.

Cold nights in August: On average, Perth can expect seven cold nights with a minimum temperature of 5 degrees or less. The greatest number of such nights in August was 15 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 (Mount 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 (Mount 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:
JR (John Relf) and Yanhui Blockley Western Australia Climate Services Centre
on, tel: (08) 9263 2222, office hours.