` Monday, 2 June 2008 - Seasonal Climate Summary for Sydney extreme rainfall - Product code IDCKGC25x0

Cold nights, sunny days in Sydney during a dry Autumn

Summary

  • below average rainfall
  • cool days - maximum temperatures below average (coolest since 1995)
  • cold nights - minimum temperatures well below average (coldest since 1984)
  • record cold nights in some western suburbs
  • sunny Autumn - 2nd sunniest on record

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Rainfall

The total Autumn rainfall of 213.0 mm at Sydney (Observatory Hill) was below the historic Autumn average1 of 372 mm. Most of the season's rainfall occurred in April with generally dry conditions in March and May. There were 33 rain days, which is below the historic average of 37 rain days. The highest Autumn rainfall totals were in the southern suburbs with Cronulla recording 309mm during Autumn. The lowest totals were in the far west, Glenmore Park recording only 81 mm for the season.

High pressure systems dominated Sydney's weather during Autumn maintaining the generally dry, settled conditions. Apart from some rain in April, very few rain bearing systems affected Sydney's weather. Cooler than average sea surface temperatures in the Tasman Sea also contributed towards the dry conditions.

Sydney's Warragamba Dam catchment area recorded Autumn rainfall totals of 100-130 mm in the lower catchment and 50-70 mm in the upper catchment (towards Goulburn). This has contributed toward a gradual decrease in 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

Temperature

Sydney had its coolest Autumn in 13 years which stands in contrast to the frequent warm Autumns Sydney has experienced in recent years. The average maximum (daytime) temperature at Observatory Hill was 22.4 °C, which is 0.5 °C below the historic Autumn average1 of 22.9°C and the coolest since 1995 (when also 22.9 °C was recorded). Below average Autumn maximum temperatures were recorded over the entire metropolitan area, especially the far west. At Richmond, the average maximum temperature was more than 1.0 °C below the historic average.

Sydney's Autumn nights were cool along the coast and cold in the western suburbs. The average minimum temperature at Observatory Hill of 14.2 °C was 0.9 °C below the historic Autumn average1 of 15.1°C, and the coldest since 1984. Average minimum temperatures in the western suburbs were 3 or 4 °C colder than coastal suburbs, and in some cases were the lowest on record for Autumn. The average minimum temperature at Richmond was the coldest since the Autumn of 1944.

The cool Autumn nights were mainly caused by several cool changes which brought cold, dry southerly air to the region. This combined with frequent clear, calm nights to produce the cool conditions. Cooler than average sea surface temperatures in the Tasman Sea also contributed towards cold nights.

The highest temperature at Sydney Observatory Hill during Autumn was 28.7 °C on 2 April while the lowest temperature was 8.4 °C on 30 April.  Corresponding extremes across the Sydney metropolitan area ranged from a high of 33.2 °C at Penrith Lakes on 20 March to a low of 0.7 °C at Camden Airport AWS on 5 May.

Some sites had their lowest Autumn mean daily minimum temperature on record.

Wind

There were 7 windy days* in coastal Sydney during Autumn, compared to the historic average of 12 windy days. The highest wind gust recorded in the Sydney metropolitan area was 78 km/hr at Richmond on 27 April associated with a strong cold front.

Other phenomena

There were 8 thunderstorms in Sydney during Autumn compared to the historical average of 5 storms. The most severe were on 7 March, 13 April and 28th/29th May when heavy rain caused local flash flooding in some suburbs. There was plentiful sunshine during Autumn with an average of 7.5 hours per day, the 2nd highest on record (the sunniest was 7.7 hours per day in Autumn 2006). Normally Sydney would expect about 6.6 hours per day for the season.

Further information

Mike De Salis
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		 33.2 °C at Penrith Lakes AWS on 20 Mar
Warmest days on average
Highest mean daily maximum temperature		 23.4 °C at Liverpool
Coolest days on average
Lowest mean daily maximum temperature		 21.1 °C at Terrey Hills AWS
Coldest day
Lowest daily maximum temperature		 15.1 °C at Springwood on 28 Apr
Coldest night
Lowest temperature		 0.7 °C at Camden Airport AWS on 5 May
Coolest nights on average
Lowest mean daily minimum temperature		 9.3 °C at Camden Airport AWS
Warmest nights on average
Highest mean daily minimum temperature		 14.2 °C at Sydney (Observatory Hill) and at Sydney Airport
Warmest night
Highest daily minimum temperature		 20.3 °C at Sydney Airport on 10 Mar and 20 Mar
Wettest overall
Highest total rainfall		 309.4 mm at Cronulla South
Driest overall
Lowest total rainfall

81.2 mm at Glenmore Park

Wettest day
Highest daily rainfall		 64.8 mm at Berowra on 8 Mar
Highest wind gust
 78 km/hr at Richmond RAAF on 27 Apr

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Records for the Sydney area

Record lowest Autumn mean daily minimum temperature
Mean daily minimum
temperature
for Autumn 2008 (°C)		 Previous lowest
for Autumn		 Years of
record		 Normal for
Autumn
Camden Airport
9.4
 9.8 in 2006 30 11.2


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Summaries for the Sydney area

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

Summary statistics for Autumn 2008
Maximum temperatures
for Autumn
(°C)		 Minimum temperatures
for Autumn
(°C)		 Rainfall
for Autumn
(millimetres)
Mean for
Autumn
2008		 Diff
from
normal		 Highest for
Autumn
2008		 Mean for
Autumn
2008		 Diff
from
normal		 Lowest for
Autumn
2008		 Total for
Autumn
2008		 Normal
for
Autumn		 Rank of
Autumn
2008		 Fraction of
Autumn
normal
Sydney (Observatory Hill) 22.4 -0.5 28.7 2 Apr 14.2 -0.9 8.4 30 Apr 213.0 371.8 low 57%
Liverpool 23.4 -0.2 32.1 20 Mar 10.6 -2.0 3.8 25 May 117.0 255.2 low 46%
Parramatta 22.8 -0.8 31.5 6 Mar 11.5 -1.5 5.3 23 May 204.1 264.5 normal 77%
Prospect Dam 23.1 -0.4 32.5 20 Mar 11.5 -1.6 4.5 29 Apr 163.2 239.4 normal 68%
Richmond RAAF 22.8 -1.1 32.1 20 Mar 10.0 -2.0 1.9 5 May 102.2 145.4 low 70%
Springwood 21.3   30.2 20 Mar 11.3   4.7 29 Apr 143.6 287.8 low 50%
Terrey Hills AWS 21.1   29.6 20 Mar 12.5   5.3 18 May 198.2

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Notes

This statement has been prepared based on information available at 2pm on Monday 2 June 2008. Some checks have been made on the data, but it is possible that results will change as new information becomes available.

1Averages:  historic average temperatures for Observatory Hill and Richmond are based on the period 1961 to 1990 which is a convention of the World Meteorological Organisation.  Average temperatures for Parramatta are based on all available data, 1968 - 2006 and Camden 1972 - 2007.  Rainfall averages and extremes for Observatory Hill are based on all years of record 1859 - 2007.

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 "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 mikede@bom.gov.au