Thursday, 1 October 2009 - Monthly Climate Summary for Perth - Product Code: IDCKGC11LO

Perth's coolest September for 38 years

Rainfall - near average: The city received 80.2 mm of rainfall over 26 days in September, compared with the average of 81 mm on about 15 days. Historically, September rainfall has ranged from 8.7 mm in 1916 to 199.1 mm in 1923. The wettest day in September 2009 was the 11th when 12.0 mm was recorded.

Rain days - equal record:  Perth recorded 26 rain days out of a possible 30 in September 2009. This equals the record for the most number of rain days in September, with 26 days also observed in 1915. The average for September is about 15 days.

Record September wet spell:  From 5th to 24th September 2009, Perth observed its longest wet spell for September on record, with 20 consecutive days of rainfall. The previous longest wet spell for September was 17 days in 1915.

Mean daily maximum temperature - below average: Perth's mean daily maximum temperature in September was 18.6°C. This is the lowest mean daily maximum temperature for September for 38 years, since the 18.6°C in 1971. The average for September is 20.1°C. Daily maxima ranged from a cold 13.9°C on the 29th, which was the lowest daily maximum temperature for September since the 13.5°C on 3rd September 1999, to a warm 26.0°C on the 27th. The mean daily maximum temperature last September was 20.6°C.

Mean daily minimum temperature - near average: Perth's mean daily minimum temperature in September was 9.8°C, compared with the average of 9.5°C. Daily minima ranged from a cold 3.1°C on the 4th, to a mild 14.6°C on the 10th. 

Mean sunshine hours - well below average: Perth's mean sunshine hours in September was 6.3 hours, which was the least sunniest September since the 6.0 hours in 1986. The average September sunshine hours is 7.7 hours. Last September, Perth recorded 7.3 hours. 

September monthly mean temperature and sunshine
Element

2009

Long- term Average

Highest

Year

Lowest

Year Records Commence
Maximum
Temperature (°C)
18.6
20.1
22.6
1987
16.8
1915
1898
Minimum Temperature (°C)
9.8
9.5
12.4
1988
8.0
2004
1898
Sunshine
(hours per day)
6.3
7.7
8.8
4 years
4.9
1907
1898
September rainfall and rain days
Element 2009 Long-term Average Highest Year Lowest Year Records Commence
Rainfall (mm)
80.2
81
199.1
1923
8.7
1916
1876
Rain days
26
15.2
26
1915
4
1877
1876

September daily extremes
Element 2009 Date Extreme Date

Records Commence

Highest daily maximum (°C)
26.0
 27/09/2009
32.7
30/9/1918
1897
Lowest daily maximum (°C)
13.9
 29/09/2009
11.4
17/09/1917
1897
Highest daily minimum (°C)
14.6
 10/09/2009 
19.5
08/09/1916
1897
Lowest daily minimum (°C)
3.1
04/09/2009
1.0
22/09/2008
1897
Wettest 24 hours to 9am (mm)
12.0
11/09/2009
51.8
14/09/1984
1876

Perth's Year to Date

Year to date rainfall - very much below average: The total rainfall for January to September this year was 563.2 mm on 97 days which was the driest January to September period since the 426.8 mm on 80 days in 2006. The average for this period is 766 mm on about 92 days. The total for the same period last year was 700 mm on 88 days.

January to September mean daily maximum temperature - equal fifth highest on record: Perth's mean daily maximum temperature for the January to September period was 24.4°C, which was the equal fifth highest mean daily maximum temperature on record with 2008. The average for the January to September period is 23.9°C. The highest mean daily maximum temperature recorded for January to September in Perth was 24.7°C in 1976 and 1978.

Perth's top 10 mean maximum temperatures
for year to date (January-September)
Year
Mean Maximum Temperatures (°C)
Departure from normal
Ranking
1976
24.7
+0.8
1
1978
24.7
+0.8
1
1985
24.5
+0.6
3
1988
24.5
+0.6
3
2008
24.4
+0.5
5
2009
24.4
+0.5
5
1972
24.3
+0.4
7
1949
24.2
+0.3
8
1983
24.2
+0.3
8
1999
24.2
+0.3
8

Climate of Perth in October

October days are generally mild, with frequent sunshine and some warm to hot days. There is typically a marked reduction in rainfall compared with September as the October rainfall average is 53 mm on about 9 days.

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

Records
Commence

Maximum temperature
(°C)
22.9
25.8
1969
18.8
1924
1897
Minimum temperature
(°C)
11.2
14.2
1969
9.3
1910
1897

Sunshine
(hours per day)

9.6
10.9
2000
5.5
1898
1898
October rainfall and rain days
Element
Average
Highest
Year
Lowest
Year
Records Commence
Rainfall (mm)
53
199.9
1890
1.0
1969
1876
Rain days
9.2
22
1898
1
1969
1876

October daily extremes
Element
Highest
Date
Lowest
Date
Records Commence
Maximum temperature (°C)
37.3
29/10/1967
11.9
08/10/1932
1897
Minimum temperature (°C)
22.2
29/10/1979
2.2
06/10/1994
1897
Rainfall 24 hours to 9am (mm)
68.2
18/10/1995
n/a
n/a
1876

Hot days in October: On average, Perth has one hot day when the maximum temperature is 32°C or higher in October. The greatest number of such days was four in 1969 and 2008.

Earliest 35°C day of the season: The earliest 35°C or greater maximum temperature of the season has occurred on 20 October 1996 with 36.9°C and on 20th October 2008 with 35.7°C.

Cold nights in October: On average, Perth can expect one night in October where the minimum temperature is 5°C or less. There were two such nights in October 2008.

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 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 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:
JR (John Relf) or Patrick Ward, Western Australia Climate Services Centre
on, tel: (08) 9263 2222, office hours.