Thursday, 30 September 2010 - Monthly Climate Summary for Perth - Product code IDCKGC21L0

Perth in September 2010: A dry and sunny September

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

Details Extremes Records Summaries Important notes the top

  • Very much below average rainfall across the Perth area.
  • Sunniest September on record.
  • Above average mean maximum temperature.
  • Below average mean minimum temperature.

Details Extremes Records Summaries Important notes the top

Rainfall

A ridge of high pressure dominated the weather over the Perth area for much of September 2010, apart from a few cold fronts during the first half of the month, resulting in very much below average rainfall. Total monthly rainfall was generally less than half of the long term September average, with several sites recording their lowest September rainfall in 30 to 40 years; while Medina Research Centre recorded its lowest September rainfall in 27 years of record. The low September rainfall follows one of the driest winters on record in the Perth area.

Despite light showers observed in the Perth area during the morning of the 30th, Perth Metro recorded nil measurable rainfall in the 24 hours to 9am on the 30th meaning the site experienced a record 18 consecutive days without rainfall (13th to 30th), breaking the previous September record of 17 days set in 1987 (1st to 17th).

Perth Metro recorded 43.6 mm of rainfall on 6 rain days in September, which was the driest September since the 35.2 mm in 2004 and well below the long term average of 80.9 mm. Historically, September rainfall at Perth Metro has ranged from 8.7 mm in 1916 to 199.1 mm in 1923. Last September (2009), Perth Metro recorded 80.2 mm on 26 days.

The total rainfall for the nine months from January to September 2010 at Perth Metro was 454.2 mm, recorded on 52 rain days, which was the driest January to September period since the 426.8 mm in 2006, and the fourth driest since records commenced in 1876. The average for the January to September period is 765.2 mm on 92.3 rain days while the total for the same period last year was 562.2 mm on 97 days. Perth Metro also experienced its least number of rain days for the nine months (January to September) on record with 52, breaking the previous record low of 72 days in 1876.

Maximum temperature

Warmer than normal daytime temperatures were experienced across the Perth area during September 2010 with a ridge of high pressure dominating the weather for much of the month resulting in several stations breaking their highest September mean daily maximum records. A particularly hot day on the 29th saw many stations record maximum temperatures of close to 30 °C, with the 29.8 °C at Swanbourne a record for the site as well as the hottest day for the month in the Perth area.

Perth Metro's mean daily maximum temperature in September was 21.8 °C, which was the equal third warmest September on record along with 1974 and 1990. Perth Metro’s warmest September was in 1987 with a mean monthly maximum of 22.6 °C while the average for September is 20.0 °C. The warmest day of the month was 29.0 °C on the 29th, which was the warmest September day since the 30.5 °C on 29 September 2006, while the coolest day was the 16.5 °C on the 12th.

Perth Metro recorded five consecutive days of over 25 °C (21st to 25th), which is the equal second longest run of this kind in September behind the six days of over 25 °C observed in 1916 (5th to 10th). On the 23rd, Perth Metro recorded its greatest diurnal temperature range (difference between the maximum and minimum temperature) for September with 22.1 °C, (min 6.1 °C, max 28.2 °C) since records commenced in 1897. The previous record for September was 21.8 °C recorded on the previous day on 22 September 2010.

Minimum temperature

A ridge of high pressure over the south of WA during much of September 2010 resulted in below average mean minimum temperatures at most sites in the Perth area. Jandakot observed the lowest overnight temperatures in the Perth area with a monthly average of 6.6 °C. Despite the cooler than normal average minimum temperatures experienced for much of the month, Perth observed an unusually warm September night overnight on the 29th. Following a warm day on the 29th, middle level cloud developed over Perth resulting in minimum temperatures in the 18 to 19 ° range and a number of September records were broken.

Perth Metro's mean daily minimum temperature in September was 8.2 °C, which was the second coldest September for Perth Metro on record behind the 8.0 °C in 2004 and well below the long term average of 9.5 °C. The coldest night of the month at Perth Metro was the 2.4 °C on the 13th, which was the coldest September night since the 1.0 °C on 22 September 2008. Perth Metro recorded seven cold nights (minimum temperature of less than 5.0 °C) which equalled the September record set in 2004. The average number of cold nights at Perth Metro during September is three. In contrast, Perth Metro recorded an overnight minimum temperature of 18.2 °C on the 30th, which was the warmest September night for 51 years since the 18.3 °C on the 2 September 1959 and ranked as the fourth warmest September night on record. Perth Metro’s warmest night in September on record was 19.5 °C observed on 8 September 1916.

Wind

The highest wind gust recorded in the Perth metropolitan area in September 2010 was 87 km/h at Rottnest Island on the 12th as a cold front crossed Perth.

Offshore winds resulting from the persistent ridge of high pressure over the south of WA were a feature of September 2010, with approximately double the average amount of east to south east winds experienced across the Perth area.

Sunshine

Perth recorded an average daily sunshine of 9.4 hours in September 2010, which was the sunniest September on record. The previous September record was 8.8 hours observed in 1914, 1929, 1954 and 1987 while the long-term September average is 7.6 hours per day.

Further information

Western Australia Climate Services Centre
Bureau of Meteorology
Phone (08) 9263 2222
Email climate.wa@bom.gov.au
Extremes in September 2010
Hottest day 29.8 °C at Swanbourne on the 29th
Warmest days on average 22.5 °C at Gosnells City
Coolest days on average 19.0 °C at Bickley
Coldest day 12.9 °C at Bickley on the 8th
Coldest night 0.5 °C at Jandakot Aero on the 13th
Coolest nights on average 6.6 °C at Jandakot Aero
Warmest nights on average 12.7 °C at Rottnest Island
Warmest night 19.2 °C at Perth Airport on the 30th
Wettest overall 47.8 mm at Swanbourne
Wettest day 20.6 mm at Jarrahdale on the 8th
Highest wind gust 87 km/h at Rottnest Island on the 12th

Details Extremes Records Summaries Important notes the top

Record lowest total September rainfall
Total rainfall
for September 2010 (mm) 		Previous lowest
for September		 Years of
record		 Average for
September
Medina Research Centre 33.6 33.8 in 2006 28 76.1

Lowest total September rainfall for at least 30 years
Total rainfall
for September 2010 (mm) 		Most recent September
this low or lower		 Years of
record		 Average for
September
Bickley 33.4 (2nd driest) 9.7 in 1969 41 122.7
Gosnells City 24.8 (2nd driest) 4.1 in 1969 41 81.6
Jarrahdale 40.6 (7th driest) 8.6 in 1969 41 125.7
Perth Airport 28.2 (3rd driest) 27.9 in 1974 36 72.0
Mundaring 46.6 (13th driest) 42.2 in 1977 33 113.0
Jandakot Aero 32.4 (2nd driest) 31.8 in 1977 33 86.1


Record highest September temperature
Highest temperature
in September 2010 (°C) 		Previous highest
for September		 Years of
record		 Average for
September
Swanbourne 29.8 on the 29th 28.9 on the 29th in 2006 18 19.5


Record highest September mean daily maximum temperature
Mean daily maximum
temperature
for September 2010 (°C) 		Previous highest
for September		 Years of
record		 Average for
September
Jandakot Aero 21.8 21.5 in 1994 20 19.8
Gosnells City 22.5 22.3 in 1994 17 20.5
Swanbourne 21.4 21.2 in 1994 17 19.5


Record highest September daily minimum temperature
Highest daily minimum
temperature
in September 2010 (°C) 		Previous highest
for September		 Years of
record		 Average for
September
Perth Airport 19.2 on the 30th 17.2 on the 28th in 1998 67 8.9
Pearce RAAF 19.1 on the 30th 19.0 on the 20th in 1985 53 8.8
Medina Research Centre 17.8 on the 30th 17.0 on the 14th in 1987 26 9.1
Jandakot Aero 18.5 on the 30th 16.0 on the 28th in 1998 21 8.1
Rottnest Island 18.6 on the 30th 17.2 on the 26th in 1999 21 12.8
Gosnells City 18.5 on the 30th 17.5 on the 3rd in 2003 18 10.0


Details Extremes Records Summaries Important notes the top

Summary statistics for September 2010
Maximum temperatures
for September
(°C)		 Minimum temperatures
for September
(°C)		 Rainfall
for September
(millimetres)
Mean for
September
2010		 Diff
from
average		 Highest for
September
2010		 Mean for
September
2010		 Diff
from
average		 Lowest for
September
2010		 Total for
September
2010		 Average
for
September		 Rank of
September
2010		 Fraction of
September
average
Bickley 19.0 +1.7 26.4 29th 7.6 -0.6 3.0 13th 33.4 120.5 v low 28%
Champion Lakes 21.0   28.2 29th 9.7   4.8 13th 31.2
Garden Island HSF 19.9 +1.4 27.8 29th 10.9 -0.9 7.3 13th 25.4 58.4 v low 43%
Gosnells City 22.5 +2.0 29.4 29th     4.2 10th 24.8 80.5 v low 31%
Jandakot Aero 21.8 +2.0 29.3 29th 6.6 -1.5 0.5 13th 32.4 84.6 v low 38%
Medina Research Centre 21.9 +1.7 29.0 29th 7.9 -1.2 2.2 3rd 33.6 76.1 lowest 44%
Pearce RAAF 21.6 +1.7 29.7 29th 8.2 -0.6 2.5 11th 35.8 69.0 low 52%
Perth Airport 22.1 +2.0 29.7 29th 8.0 -0.9 2.7 13th 28.2 71.3 v low 40%
Perth Metro* 21.8 +1.8 29.0 29th 8.2 -1.3 2.4 13th 43.6 80.9 v low 54%
Rottnest Island 19.5 +0.8 25.6 29th 12.7 -0.1 8.6 13th 36.6 53.7 low 68%
Swanbourne 21.4 +1.9 29.8 29th 9.8 -1.1 4.9 13th 47.8 80.4 low 59%

Details Extremes Records Summaries Important notes the top

Daily rainfall
Central Coast (09)123456789101112131415161718192021222324252627282930
Bickley 1.6 0.2 - - - - - 17.8 8.2 - - 5.4 - - - - - - - - - - - - 0.2 - - - - -
Champion Lakes 8.2 - - - - - - 12.4 6.8 - - 3.8 - - - - - - - - - - - - - - - - - -
Garden Island HSF 1.4 - - 3.0 0.2 - - 7.0 9.0 0.2 - 4.4 0.2 - - - - - - - - - - - - - - - - -
Gosnells City 2.6 - - 0.2 - - - 12.0 5.8 - - 4.0 0.2 - - - - - - - - - - - - - - - - -
Jandakot Aero 7.4 - - 0.6 - - - 14.2 3.2 - - 7.0 - - - - - - - - - - - - - - - - - -
Jarrahdale 2.2 - - 0.2 - 0.2 - 20.6 10.2 0.2 0.2 6.0 0.2 - 0.4 - - - - - - - - - 0.2 - - - - -
Medina Research Centre 4.6 - - 0.6 - - 0.4 10.8 12.0 - - 5.2 - - - - - - - - - - - - - - - - - -
Mundaring 4.2
0.2 1.0 0.2 0.2
13.6 19.0 0.2 0.2 7.0 0.2


0.2






0.2 0.2



Pearce RAAF 11.0 - - 0.8
- - 11.2 5.8 - - 7.0 - - - - - -
- - - - - - - - - - -
Perth Airport 2.0 - - 1.4 - - - 11.4 7.6 - - 5.8 - - - - - - - - - - - - - - - - - -
Perth Metro 10.0 - - 2.8 0.2 - - 12.0 10.6 - - 8.0 - - - - - - - - - - - - - - - - - -
Rottnest Island 20.2 - - 3.6 0.4 - - 5.6 1.8 - - 5.0 - - - - - - - - - - - - - - - - - -
Serpentine 2.0 - - - - - - 12.2 7.2 - - 3.6 - - - - - - - - - - - - - - - - - -
Swanbourne 12.6 - - 3.0 0.2 - - 13.0 9.4 - - 8.8 - - - - - - - - - - - - 0.2 - - - - 0.6

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.

Details Extremes Records Summaries Important notes the top

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 Thursday 30 September 2010. 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.
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 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

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