Perth in September 2011: A wetter than average month

This statement was prepared before all data for the period were available. This may affect some of the statistics presented.
  • Rainfall: Average to above average.
  • Maximum temperature: Near average.
  • Minimum temperature: Near average.
This statement was prepared before all data for the period were available. This may affect some of the statistics presented.

Rainfall

Rainfall across the Perth metropolitan area during September 2011 was near average at most locations, however some sites in the eastern suburbs and hills saw above average rainfall. Rainfall totals on the metropolitan plain were generally in the 80 to 130 mm range, while Mundaring in the hills was the wettest in the Perth area with 175.0 mm. Perth Airport, Jandakot Aerodrome and Perth Metro observed their wettest September in 10 or more years.

A strong westerly flow across the south of WA, with embedded cold fronts, brought wet weather to Perth during the first few days of September. Moderate rainfall was registered across the Perth area, with daily totals in the 10 to 30 mm range on the 2nd, with lighter falls observed on subsequent days. After a lengthy break due to a very strong high pressure system, a number of cold fronts brought moderate falls across the Perth area during the second half of the month. Bedfordale observed 47.2 mm in the 24 hours to 9am on the 16th which was their highest daily total in its 18 years of record, and was also the highest daily total of September 2011 in the Perth area.

Perth Metro recorded 109.2 mm on 16 rain days in September 2011 which is above average and the wettest September since the 115.2 mm on 18 rain days in 2001. The average for September is 80.6 mm on 15.3 rain days with September rainfall totals ranging from 8.7 mm in 1916 to 199.1 mm in 1923. Last September (2010), Perth Metro recorded 43.6 mm on 6 rain days.

Perth Metro recorded 691.8 mm of rainfall on 86 rain days in the first 9 months of 2011 (January to September) which is below average, but still the wettest since the 700.0 mm on 88 rain days in 2008.

Maximum temperature

Mean daily maximum temperatures were near average across the Perth area during September 2011. Two consecutive warm days were experienced on the 11th and 12th, with daily maxima across Perth in the low to mid 20's, which is 3 to 4 °C warmer than normal. The daily maximum temperature of 26.2 °C at Perth Airport on the 12th was the highest temperature of the month in the Perth region. A few cool to cold days were experienced at the beginning and latter parts of the month due to cold fronts crossing the region. During this time, daily maxima were generally in the low to mid teens, which is 2 to 4 °C cooler than normal for most sites. The daily maximum temperature of 12.7 °C at Bickley on the 27th was the lowest temperature of September 2011 in the Perth area.

Perth Metro's mean daily maximum temperature in September was 20.5 °C which was close to the average of 20.1 °C. Daily maxima ranged from a cool 17.1 °C on the 2nd and the 27th to a warm 24.5 °C on the 12th.

Perth Metro's mean daily maximum temperature for the first 9 months of 2011 (January to September) was 25.3 °C, which was the warmest year to date since records commenced in 1897, breaking the record of 24.7 °C set in 1976 and 1978. The average for the 9 month (January to September) period is 24.0 °C.

Minimum temperature

Minimum temperatures across Perth during September 2011 were near average. A few warm nights were experienced in the middle of the month, with daily minima in the low to mid teens for most sites. The daily minimum temperature of 16.5 °C recorded at Gosnells City on the 21st was the highest minimum temperature of the month for the Perth area. Cold nights (daily minima less than 5 °C ) were observed near the end of the month at most inland sites. Jandakot Aerodrome observed the coldest night in the Perth area during September 2011 with 3.4 °C on the 29th.

Perth Metro's mean daily minimum temperature in September was 9.4 °C, equal with the long term average. Daily minima ranged from a cold 4.9 °C on the 29th to a mild 14.4 °C on the 16th.

Wind and Sunshine

A strong cold front crossed the Perth area on the 18th and caused severe wind gusts at Bickley (100 km/h), Rottnest Island (98 km/h) and Garden Island (91 km/h). Widespread though minor damage was reported in the Perth area, with the most serious damage in the southeast suburbs of Maddington and Westfield where trees fell on houses.

Perth recorded an average daily sunshine of 7.6 hours in September 2011, close to the average of 7.7 hours.

Further information

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Extremes in September 2011
Hottest day 26.2 °C at Perth Airport on the 12th
Warmest days on average

21.1 °C at Gosnells City

Coolest days on average 17.3 °C at Bickley
Coldest day 12.7 °C at Bickley on the 27th
Coldest night 3.4 °C at Jandakot Aero on the 29th
Coolest nights on average 8.1 °C at Jandakot Aero
Warmest nights on average 12.9 °C at Rottnest Island
11.1 °C at Swanbourne (mainland)
Warmest night 16.5 °C at Gosnells City on the 21st
Wettest overall 175.0 mm at Mundaring
Wettest day 47.2 mm at Bedfordale on the 16th
Highest wind gust

100 km/h at Bickley on the 18th


Record highest September daily rainfall
Highest daily rainfall
in September 2011 (mm)
Previous highest
for September
Years of
record
Bedfordale 47.2 on the 16th 40.6 on the 29th in 2001 18



Highest total September rainfall for at least 10 years
Total rainfall
for September 2011 (mm)
Most recent September
this high or higher
Years since
higher
Average for
September
Perth Airport 103.6 114.4 in 1998 13 71.8
Jandakot Aero 114.4 140.8 in 1999 12 85.4
Perth Metro* 109.2 115.2 in 2001 10 80.6



Summary statistics for September 2011
Maximum temperatures
for September
(°C)
Minimum temperatures
for September
(°C)
Rainfall
for September
(millimetres)
Mean for
September
2011
Diff
from
average
Highest for
September
2011
Mean for
September
2011
Diff
from
average
Lowest for
September
2011
Total for
September
2011
Average
for
September
Rank of
September
2011
Fraction of
September
average
Bickley 17.3 -0.1 23.5 12th 8.6 +0.5 4.7 28th 168.4 121.6 high 138%
Champion Lakes 19.4   23.7 12th 10.3   4.3 28th
Garden Island HSF 18.9   22.2 11th 12.0   7.8 28th 72.8 59.8 average 122%
Gosnells City 21.1 +0.5 26.0 12th         114.9 81.2 high 142%
Jandakot Aero 19.9 0.0 24.2 12th 8.1 0.0 3.4 29th 114.4 85.4 high 134%
Medina Research Centre 20.2 0.0 25.0 11th 9.5 +0.5 4.7 28th 89.9 76.6 average 117%
Pearce RAAF 19.9 -0.1 25.9 12th 8.7 0.0 4.6 28th 78.8 69.1 average 114%
Perth Airport 20.4 +0.3 26.2 12th 8.9 +0.1 3.8 28th 103.6 71.8 high 144%
Perth Metro* 20.5 +0.3 24.7 12th 9.4 0.0 4.9 29th 109.2 80.6 high 135%
Rottnest Island 18.6 -0.1 21.7 12th 12.9 +0.1 10.3 28th 54.4 58.5 average 93%
Swanbourne 20.1 +0.5 23.9 11th 11.1 +0.2 6.8 28th 80.2 80.4 average 100%

Daily maximum temperature
Central Coast (09)123456789101112131415161718192021222324252627282930
Bickley19.613.315.315.316.917.917.016.717.819.521.123.519.120.018.217.418.013.816.518.114.412.917.720.318.113.812.715.620.2
Champion Lakes21.416.317.318.418.319.219.119.320.621.323.323.720.723.119.320.219.816.818.420.017.516.319.421.119.416.415.818.321.2
Garden Island HSF20.516.817.718.617.717.319.320.220.719.922.221.918.219.519.620.520.017.118.620.717.915.918.218.920.117.116.818.019.1
Gosnells City23.517.118.420.019.221.020.522.023.525.226.022.723.921.122.021.518.019.521.718.517.021.023.021.318.020.023.2
Jandakot Aero22.217.118.618.819.319.519.819.921.021.423.924.221.021.819.121.420.617.318.920.918.516.519.721.520.517.417.418.521.8
Medina Research Centre22.516.918.519.118.919.620.020.421.722.025.024.020.822.220.421.721.417.418.720.918.317.020.921.417.017.019.721.5
Pearce RAAF22.415.517.317.718.719.519.018.819.620.723.525.920.622.420.721.521.517.319.121.019.216.119.522.420.220.217.018.221.9
Perth Airport23.116.718.319.019.820.620.320.020.822.424.226.221.822.921.320.821.117.819.121.219.016.920.622.320.417.517.218.522.6
Perth Metro22.917.118.419.219.119.820.020.221.122.423.924.721.723.021.321.520.717.820.221.120.217.519.921.720.817.817.119.622.2
Rottnest Island20.416.517.518.318.716.617.418.318.819.421.321.718.120.419.220.319.617.018.820.217.916.117.819.420.016.715.917.319.2
Swanbourne21.316.919.119.520.119.720.920.921.921.723.923.520.520.819.821.120.217.320.320.918.617.319.721.021.417.417.018.922.4

This table is very wide; you may have to scroll sideways to see all the days, and you may need to set the paper to 'landscape' to print.
The temperatures in this table are coloured by
their difference from the long-term average for the period
-10.0 -9.0 -8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0 +1.0 +2.0 +3.0 +4.0 +5.0 +6.0 +7.0 +8.0 +9.0 +10.0 °C difference from average


Daily minimum temperature
Central Coast (09)123456789101112131415161718192021222324252627282930
Bickley10.110.35.89.59.26.56.46.36.85.67.010.812.111.013.213.29.08.68.210.911.06.85.77.39.011.26.94.76.07.5
Champion Lakes10.012.78.012.29.28.07.310.19.910.310.99.111.112.214.315.59.911.310.711.513.410.27.09.08.513.87.84.37.812.3
Garden Island HSF12.713.612.313.914.311.110.710.910.610.310.78.515.310.612.915.614.412.012.114.915.110.99.69.611.613.812.17.810.012.2
Gosnells City8.77.411.68.07.37.19.79.59.511.011.211.814.614.911.511.616.59.75.97.013.67.99.712.0
Jandakot Aero6.912.87.110.66.24.55.07.36.96.24.34.09.27.713.113.86.411.211.89.812.59.04.44.45.313.19.63.53.411.5
Medina Research Centre8.013.18.612.19.46.58.07.47.98.46.85.610.39.412.813.88.111.510.714.314.18.85.67.413.911.04.76.311.5
Pearce RAAF8.312.97.410.87.46.45.48.48.69.97.35.18.97.912.812.39.111.411.011.09.58.36.65.46.412.47.74.66.012.2
Perth Airport8.713.27.511.07.36.37.27.18.29.06.97.79.011.213.013.99.011.511.610.512.07.75.24.76.712.78.23.84.711.6
Perth Metro8.913.28.311.28.37.48.86.88.68.76.96.49.611.513.914.49.212.211.912.012.49.56.15.27.113.49.85.14.911.6
Rottnest Island14.813.411.012.913.912.211.510.811.611.213.114.215.114.216.315.413.512.111.815.315.310.411.312.214.413.610.710.312.713.2
Swanbourne10.813.210.813.214.47.88.17.89.49.510.09.713.212.115.015.211.512.211.814.815.89.68.57.910.113.810.86.87.611.6

This table is very wide; you may have to scroll sideways to see all the days, and you may need to set the paper to 'landscape' to print.
The temperatures in this table are coloured by
their difference from the long-term average for the period
-10.0 -9.0 -8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 0.0 +1.0 +2.0 +3.0 +4.0 +5.0 +6.0 +7.0 +8.0 +9.0 +10.0 °C difference from average


Daily rainfall
Central Coast (09)123456789101112131415161718192021222324252627282930
Bedfordale 3.8 10.0 0.2 0.4 47.2 5.4 20.2 7.8 14.4 »» 20.8 3.8 5.0 -
Bickley - 28.2 11.8 5.4 0.4 0.2 - - - - - - 0.2 - - 18.6 13.6 26.4 7.6 1.0 1.6 16.2 - - - 12.6 10.4 14.2 - -
Champion Lakes




- - - - - - - - - - 4.8 0.6 13.2 1.2 - 1.6 13.8 - - - 7.2 6.2 3.4 - -
Garden Island HSF 0.2 15.0 0.8 2.2 0.2 - - - - - - - - - - 14.4 4.2 17.6 1.0 0.2 4.6 7.4 0.2 - - 1.6 1.4 1.6 0.2 -
Gosnells City »» 24.4 3.8 4.2 0.6 - - -
- - - - - 0.2 8.8 »» »» 4.2 0.4 5.6 16.6 0.2 »» »» 11.8 »» 10.4 0.1 -
Jandakot Aero - 21.8 3.0 7.2 0.2 - - - - - - - - - 0.8 18.4 5.6 16.4 4.4 0.6 2.2 12.2 - - - 6.2 13.2 2.2 - -
Jarrahdale - 31.4 4.4 9.2 0.4 - 0.2 - - - - 0.2 - 0.2 - 0.2 0.4 18.8 8.0 1.4 18.6 22.2 - 0.4 - 8.4 5.8 7.4 0.4 -
Medina Research Centre - 15.0 1.4 4.2 1.3 - - - - - - - - - 0.2 11.4 2.5 13.4 4.5 0.3 13.4 8.6 - - - 5.8 3.2 4.7 - -
Mundaring 0.2 35.4 17.0 3.6 1.0 0.2 0.2
0.2


0.8
1.4 11.6 13.0 20.0 10.8 1.6 4.2 17.4


16.2 6.8 13.2 0.2
Pearce RAAF - 11.2 10.2 2.0 1.0 - - - - - - - - - 2.4 10.6 1.6 10.0 3.2 - 0.4 4.8 - - - »» 12.0 3.4 - -
Perth Airport - 16.0 6.8 1.6 - - - - - - - - - - - 19.0 3.2 13.6 4.4 0.4 3.6 13.6 - - - 12.6 4.0 4.8 - -
Perth Metro 0.2 15.0 6.4 2.4 0.6 - - - - - - - - - 0.6 16.0 6.2 17.6 3.0 1.0 1.0 13.2 - - - 15.6 5.8 4.6 - -
Rottnest Island - 10.8 0.8 5.0 - - - - - - - - 0.8 - 0.8 8.0 0.2 7.8 1.4 - 1.8 6.6 - - - 4.6 2.0 3.8 - -
Serpentine - 19.6 2.6 4.4 - 0.2 - - - - - - - - - 10.0 3.8 26.2 4.8 1.0 9.0 14.0 0.2 - - 3.2 4.4 5.4 0.2 -
Swanbourne 0.2 17.8 1.2 2.2 - - - - - - - - 0.2 - 0.4 8.2 9.2 11.2 3.0 1.0 0.6 13.2 - - - 5.6 4.2 2.0 - -

Most values are the precipitation in the 24 hours to 9 am on the day indicated. Days marked with »» are part of a longer accumulation, which is marked like this on the final day. Values over 100 mm have been rounded to the nearest whole millimetre. Days marked with - have a rainfall report of zero; days left blank have no rainfall report (which often indicates no rain fell).
This table is very wide; you may have to scroll sideways to see all the days, and you may need to set the paper to 'landscape' to print.


Notes

This statement was prepared before all data for the period were available. This may affect some of the statistics presented.

A Monthly 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 11 am on Friday 30 September 2011. 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

Media
(03) 9669 4057
Enquiries