Tuesday, 2 September 2008 - Seasonal Climate Summary for Sydney extreme rainfall - Product code IDCKGC25x0

Sydney has coldest winter for 10 years

Summary

  • coldest average daytime maximum temperatures since 1998
  • close to average minimum temperatures
  • below average rainfall
  • less sunshine in Winter - cloudiest since 1998

An archive of previous seasonal summaries for Sydney extreme rainfall is also available, as are summaries for other states and many other climate summaries and diagnostics.

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Rainfall

The total Winter rainfall of 261.0 mm at Sydney (Observatory Hill) was below the historic Winter average1 of 311 mm. About half of the season's rainfall occurred in June with below average rainfall in July and August. There were 34 rain days, which is above the historic average of 31 rain days. The highest Winter rainfall totals were in the eastern suburbs with Randwick recording 357mm for the season. The lowest totals were in the far west, Willmot recording only 98 mm for the season.

Apart from some moderate rain in June, cold, dry southwesterly winds prevailed for extended periods during July and August with high pressure systems maintaining mostly settled conditions over the metropolitan area. Consequently mostly light showers were associated with the passage of the occasional cold front and southerly airstream.

Sydney's Warragamba Dam catchment area recorded Winter rainfall totals of 120-140 mm in the lower catchment and 90-100 mm in the upper catchment (towards Goulburn). This has contributed towards generally steady storage levels over the season. 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

Although Sydney's average Winter maximum temperature was slightly above the historical average, it was still the lowest average maximum temperature for 10 years. The average maximum (daytime) temperature at Observatory Hill was 17.7 °C, which is 0.7 °C above the historic Winter average1 of 17.0 °C and the coolest since 1998 (when 17.3 °C). Slightly below average Winter maximum temperatures were recorded over the remainder of the Sydney metropolitan area.

Sydney's Winter nights were very close to, or slightly above the historical average. The average minimum temperature at Observatory Hill of 9.4 °C was 0.7 °C above the historic Winter average1 of 8.7°C. Average minimum temperatures in the far western suburbs were more than 5 °C colder than coastal suburbs but very close to normal winter averages. During Winter there were extended periods with cold nights. At Sydney Observatory Hill there were 25 consecutive nights (22 July to 15 Aug) with minimum temperatures below 10 °C, the longest spell since June-July 1971 (when 26 consecutive nights below 10 °C). At Richmond there was 72 consecutive nights (21 June to 31 Aug) with minimums below 8 °C, a record long spell. The previous longest spell was 48 days below 8 °C in June and July 1943.

The cool Winter nights were largely a result of extended periods of unusually strong high pressure systems in the Southern Ocean, mainly during July and August, directing south-westerly winds over Sydney and NSW which combined with numerous clear, calm nights.

The highest temperature at Sydney Observatory Hill during Winter was 23.1 °C on 14 July while the lowest temperature was 5.3 °C on 19 August.  Corresponding extremes across the Sydney metropolitan area ranged from a high of 23.1 °C at Sydney Observatory Hill on 14 July and at Sydney Olympic Park on 26 August. The lowest temperature was -2.9 °C at Richmond RAAF on 19 August.

Wind

There were 17 windy days* in coastal Sydney during Winter, compared to the historic average of 13 windy days. The prevailing coastal wind direction was between west and south for about 56% of the time during the afternoons. The highest wind gust recorded in the Sydney metropolitan area was 94 km/h at Penrith Lakes AWS on 2 August associated with several strong cold fronts. On 28 July a wind gust of 98 km/h was recorded at Wattamolla in the Royal National Park south of Sydney.

Other phenomena

There were 4 thunderstorms in Sydney during Winter which is average for the season. The most severe was on 27 July when a hailstorm hit Bankstown, Concord, Chatswood and Killara, covering the ground in small hail and causing drifts 15cm deep. Heavy rain on 5 June caused minor flooding at Audley Weir in Sydney's south. It was partly cloudy Winter with an average of 6.2 hours of sunshine per day, the lowest since 1998 (when 5.2 hours per day). Normally Sydney would expect about 6.8 hours per day for the season.

Further information

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

* Windy day defined as average wind speed of 40 km/hr or more over a 10 minute period.

Extremes for the Sydney area

Hottest day
Highest temperature
 23.1 °C at Sydney (Observatory Hill) on 14 Jul
and at Sydney Olympic Park on 26 Aug
Warmest days on average
Highest mean daily maximum temperature
 18.0 °C at Liverpool and at Sydney Olympic Park
Coolest days on average
Lowest mean daily maximum temperature
 16.1 °C at Springwood
Coldest day
Lowest daily maximum temperature
 10.5 °C at Terrey Hills AWS on 22 Aug
Coldest night
Lowest temperature
 -2.9 °C at Richmond RAAF on 19 Aug
Coolest nights on average
Lowest mean daily minimum temperature
 4.0 °C at Richmond RAAF
Warmest nights on average
Highest mean daily minimum temperature
 9.4 °C at Sydney (Observatory Hill)
Warmest night
Highest daily minimum temperature
 15.6 °C at Sydney Airport on 4 Jun
Wettest overall
Highest total rainfall
 356.6 mm at Randwick
Driest overall
Lowest total rainfall
 98.0 mm at Willmot
Wettest day
Highest daily rainfall
 85.2 mm at North Turramurra on 5 Jun
Highest wind gust
 94 km/h at Penrith Lakes AWS on 2 Aug

AWS = Automatic Weather Station

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Records

Nil recorded

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Summaries for the Sydney area

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

Summary statistics for Winter 2008
Maximum temperatures
for winter
(°C)		 Minimum temperatures
for winter
(°C)		 Rainfall
for winter
(millimetres)
Mean for
winter
2008		 Diff
from
normal		 Highest for
winter
2008		 Mean for
winter
2008		 Diff
from
normal		 Lowest for
winter
2008		 Total for
winter
2008		 Normal
for
winter		 Rank of
winter
2008		 Fraction of
winter
normal
Sydney (Observatory Hill) 17.7 +0.7 23.1 14 Jul 9.4 +0.7 5.3 19 Aug 261.0 310.8 average 84%
Bankstown Airport AWS 17.5 -0.5 22.5 30 Jun 6.1 +0.1 0.5 10 Aug 182.2 170.3 average 107%
Camden Airport AWS 17.5 -0.5 22.1 26 Aug 4.4 +0.7 -2.4 30 Jun 142.6 141.0 average 101%
Parramatta North 17.9 -0.1 22.2 30 Jun 6.8 -0.1 1.8 19 Aug 169.0 188.3 average 90%
Penrith Lakes AWS 17.9 -0.7 22.7 30 Jun 6.0 -0.1 0.3 23 Jul 138.8 114.1 high 122%
Prospect Reservoir 17.4 -0.2 22.1 26 Aug 6.5 -0.3 1.0 9 Aug 162.7 183.5 average 89%
Richmond RAAF 17.6 -0.8 22.7 11 Jun 4.0 -0.2 -2.9 19 Aug 124.2 120.4 average 103%
Springwood* 16.1   21.5 26 Aug 7.0   2.4 12 Jul 144.0 190.3 average 76%
Terrey Hills AWS* 16.2   20.7 12 Jun 7.9   2.9 12 Jul 245.2

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

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Notes

This statement has been prepared based on information available at 11 am on Tuesday 2 September 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
Bureau of Meteorology
Phone (02) 9296 1555
Email reqnsw@bom.gov.au