Wednesday, 1 October 2008 - Monthly Climate Summary for Sydney - Greater Sydney - Product code IDCKGC25x0

Sydney during September: Warm and sunny with above average rainfall

Summary

Warm, sunny month. Although rainfall was above average, the majority fell on one or two days early in the month with generally dry conditions prevailing for the remainder.

An archive of previous monthly summaries for Sydney - Greater Sydney is also available, as are summaries for other states and many other climate summaries and diagnostics.

Details

  • Above average rainfall
  • Warm month with above average maximum and minimum temperatures
  • First September in 150 years to record 2 days above 32°C
  • 11th consecutive year with above average maximum temperatures for September
  • 14th consecutive year with above average minimum temperatures for September
  • Sunny month averaging 8.5 hours of sunshine per day

Rainfall

Sydney had above average rainfall for the month of September with Observatory Hill recording 99.2 mm compared with the historical September average1 of 69.2 mm. September is normally Sydney's driest month. There were 10 rain days during September which is average for the month. Nearly all the rain fell on two days early in the month in association with a low pressure system which formed off the NSW coast. The remainder of the month was virtually dry as a prevailing high pressure system and dry NW winds maintained generally settled conditions.

The heaviest rainfall was recorded on the North Shore with over 100 mm at most locations. The lowest rainfall occurred in the far west where less than 50 mm was recorded. The highest monthly total was 126.4 mm at Turramurra in Sydney's north while the lowest was 30 mm at Willmot in the far western suburbs.

Between 40 and 70 mm of rain was recorded over the Warragamba Dam catchment during September, contributing to a slight rise in storage levels over the month. Recent rainfall in Sydney's drinking water catchments can be found on the Sydney Catchment Authority web site http://www.sca.nsw.gov.au/dams/rainfall.html

Temperatures

September was a particularly warm month for Sydney, with maximum temperatures above the historic averages throughout the Sydney basin. The mean maximum temperature at Observatory Hill of 21.4°C was 1.5°C above the historical September average1. This is now the 11th consecutive year with September mean maximum temperatures being above the historical average. The last time Sydney recorded a cool September (below average maximum temperatures) was back in 1997. The warm daytime temperatures were largely a result of prevailing NE - NW winds and generally clear skies.

For the first time in 150 years of record Sydney has recorded two days in September with a maximum temperature above 32°C, on the 20th and 28th. Most Septembers usually record zero such days or very occasionally, one day.

However, despite the generally mild days, very cold daytime temperatures were experienced on the 6th when heavy cloud cover, strong southerly winds and continuous rain caused record and near record low maximum temperatures. The maximum at Bankstown Airport reached only 12.6°C, the lowest for September in 40 years of record. At Sydney Airport the maximum temperature was the lowest September maximum for 13 years.

Overnight temperatures were above average in coastal Sydney, however, over much of the western suburbs, minimum temperatures were close to or slightly below average. The average minimum temperature at Observatory Hill was 12.2°C which is above the historical mean for September of 11.0°C. This is now the 14th consecutive year with above average September minimum temperatures in Sydney. The last time Sydney experienced below average minimum temperatures in September was back in 1994. The mild overnight conditions along the coast was partly due to the moderating influence of the ocean and mild NE - NW winds.

Some sites had their coldest September day (lowest maximum temperature) on record.

Wind

The prevailing wind direction along coastal Sydney was NE to NW during September with nearly 50% of all winds from this quarter. The highest wind gust in the Sydney area was 100 km/h at Wattamolla (Royal N.P.) on the 6th. Strong winds were observed at Sydney Airport on 7 days which is above the average for September of 5 windy days.

Other phenomena

A thunderstorm was reported from parts of NW Sydney and at Sydney Airport on the 14th and was accompanied by small hail. However, no thunderstorms were reported at the official Sydney city site during the month. The historical average for September is 2 storms. There was plentiful sunshine during the month with an average of 8.5 hours per day, compared to the historical average of 7.2 hours per day.

Further information

NSW Climate Services Centre
NSW Regional Office
Bureau of Meteorology
Phone (02) 9296 1555
Email reqnsw@bom.gov.au

Extremes

Hottest day
Highest temperature
34.5°C at Sydney Olympic Park on the 28th
Warmest days on average
Highest mean daily maximum temperature
23.1°C at Penrith Lakes AWS
Coolest days on average
Lowest mean daily maximum temperature
20.6°C at Terrey Hills AWS
Coldest day
Lowest daily maximum temperature
11.6°C at Springwood on the 5th
Coldest night
Lowest temperature
−0.3°C at Camden Airport AWS on the 11th
Coolest nights on average
Lowest mean daily minimum temperature
7.0°C at Campbelltown (Mount Annan)
Warmest nights on average
Highest mean daily minimum temperature
12.2°C at Sydney (Observatory Hill)
Warmest night
Highest daily minimum temperature
19.8°C at Sydney (Observatory Hill) on the 28th
Wettest overall
Highest total rainfall
126.4 mm at Turramurra
Driest overall
Lowest total rainfall
30.0 mm at Willmot
Wettest day
Highest daily rainfall
85.8 mm at St Ives on the 6th
Highest wind gust
Eastern Sydney region
100 km/h at Wattamolla (Royal N.P.) on the 6th
85 km/h at Sydney Airport on the 22nd
Western Sydney
80 km/h at Penrith Lakes AWS on the 14th

AWS = Automatic Weather Station


Records

Record lowest September daily maximum temperature
Lowest daily maximum
temperature
in September 2008 (°C)
Previous lowest
for September
Years of
record
Normal for
September
Bankstown Airport AWS 12.6 on the 6th 13.1 on the 24th in 1970 40 21.0



Summaries

This table is very wide and may not fit if printed.

Summary statistics for September 2008
Maximum temperatures
for September
(°C)
Minimum temperatures
for September
(°C)
Rainfall
for September
(millimetres)
Mean for
September
2008
Diff
from
normal
Highest for
September
2008
Mean for
September
2008
Diff
from
normal
Lowest for
September
2008
Total for
September
2008
Normal
for
September
Rank of
September
2008
Fraction of
September
normal
Sydney (Observatory Hill) 21.4 +1.5 32.9 28th 12.2 +1.2 7.0 10th 99.2 69.2 high 142%
Bankstown Airport AWS 22.2 +1.2 33.4 28th 9.1 +0.7 3.1 11th 44.4 45.4 average 98%
Parramatta North 22.4 +1.5 33.1 28th 9.4 +0.1 4.2 2nd 88.5 53.6 high 165%
Penrith Lakes AWS 23.1 +1.8 33.4 28th 9.2 −0.2 3.1 11th 39.4 40.1 average 98%
Prospect Reservoir 22.7 +2.0 32.8 20th 9.3 −0.1 3.1 10th 50.0 47.4 average 106%
Richmond RAAF 22.2 +1.2 32.6 20th 7.6 −0.5 0.5 2nd 33.2 58.0 average 57%
Springwood* 21.1   31.3 20th 9.3   3.1 11th 63.2 56.3 average 112%
Terrey Hills AWS* 20.6   32.1 28th 10.9   5.3 10th 104.2

* new stations, no historic average temperatures available and no historic average rainfall available for Terrey Hills


Notes

This statement has been prepared based on information available at 11 am on Wednesday 1 October 2008. Some checks have been made on the data, but it is possible that results will change as new information becomes available.

Normals 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, as they cannot then be calculated reliably.
The median is sometimes more representative than the mean of long-term average ("normal") 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, normal in decile 4 to 7, high in decile 8 or 9 and very high is in decile 10).
The Fraction of normal shows how much rain has fallen this time as a percentage of the long-term mean.

Further information

NSW Climate Services Centre
NSW Regional Office
Bureau of Meteorology
Phone (02) 9296 1555
Email reqnsw@bom.gov.au