Monday, 2 June 2008 - Monthly Climate Summary for Sydney extreme rainfall - Product code IDCKGC15x0

Driest May in 150 years of record in Sydney

Summary

  • Driest May on record with total of 3.0 mm.
  • Mild days - slightly above average daytime temperatures
  • Cold nights - well below average minimum temperatures
  • Sunny month - well above average sunshine hours

Rainfall

Sydney (Observatory Hill) experienced its driest May in 150 years of record. The official site at Observatory Hill recorded only 3.0 mm which is well below the historic May average1 of 121.5 mm. The previous lowest total was 3.7 mm in 1957. There were 5 rain days during May which is also well below the May average of 12 days. Only 6 previous Mays have had fewer than 5 rain days. The dry, stable conditions were caused by a persistant ridge of high pressure over Sydney and NSW and weak rain bearing systems.

The dry conditions extended over parts of the metropolitan area with many areas recording less than 10 mm for the month, and record or near record low May totals at several suburban sites (see table below). However, because of the patchy nature of storms, some suburbs experienced very heavy showers causing local flash flooding. Such storms, often accompanied by hail, occurred at Cronulla (57 mm) and Campbelltown (37 mm) on the 28th and 29th and Glenorie on the 13th (23.4 mm).

Only light rain fell in the Warragamba Dam catchment during May (generally less than 20 mm) which contributed towards a slight decline in storage levels. 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.

Some sites had their lowest May rainfall on record.

Temperature

Daytime temperatures were generally mild across the Sydney basin during May. The average maximum temperature at Observatory Hill of 20.5 °C was 0.2 °C above the historic May average 1. Slightly above average maximum temperatures were recorded at all sites across the Sydney metropolitan area.

Sydney's nights were cool to cold throughout with below average minimum temperatures along the coast and well below average minimums over inland suburbs. The average minimum temperature at Sydney Observatory Hill was 11.4 °C which is 0.6 °C below the historic May average 1. Western suburbs experienced much colder nights with minimum temperatures about 2-3 °C below the historic average. At Camden, the average May minimum temperature of 5.1 °C was the lowest recorded since 1982. Several cool changes during the month which introduced cold, dry air to the region combined with numerous clear nights producing favourable conditions for low overnight temperatures.

Wind

There was a dominance of winds from east to south during the afternoons with more than 70% of all coastal winds from this direction. Normally Sydney would expect winds from this direction less than 50% of the time. The highest wind gust in the greater Sydney area was 65 km/hr at Sydney Airport on the 17th.

Other phenomena

Thunderstorms occurred over Sydney on the 13th, 28th and 29th, some producing heavy hail and local flash flooding. Widespread fog on the morning of the 15th reduced visibility to only 100 metres over many parts of the city. Sunshine was plentiful during May with an average of 7.6 hours per day, making it the 4th sunniest May on record. Normally Sydney would expect around 6.1 hours of sunshine per day.

Further information

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

Extremes for the Sydney area

Hottest day
Highest temperature
24.9 °C at Sydney Olympic Park on the 15th
Warmest days on average
Highest mean daily maximum temperature
21.3 °C at Sydney Olympic Park
Coolest days on average
Lowest mean daily maximum temperature
19.0 °C at Springwood
Coldest day
Lowest daily maximum temperature
15.9 °C at Terrey Hills on the 18th
Coldest night
Lowest temperature
0.7 °C at Camden Airport on the 5th
Coolest nights on average
Lowest mean daily minimum temperature
5.1 °C at Camden Airport
Warmest nights on average
Highest mean daily minimum temperature
11.4 °C at Sydney (Observatory Hill)
Warmest night
Highest daily minimum temperature
15.2 °C at Sydney (Observatory Hill) on the 17th
Wettest overall
Highest total rainfall
63.5 mm at Cronulla South
Driest overall
Lowest total rainfall
1.6 mm at Glenmore Park
Wettest day
Highest daily rainfall
57.0 mm at Cronulla South on the 29th
Highest wind gust
65 km/hr at Sydney Airport on the 17th

 


Records for the Sydney area

Record lowest total May rainfall
Total rainfall
for May 2008 (mm)
Previous lowest
for May
Years of
record
Normal for
May
Sydney (Observatory Hill)
3.0
3.7 in 1957 149 121.5
Sans Souci
3.0
4.5 in 1957 107 107.5
Randwick
3.2
4.6 in 1957 98 118.6
Turramurra
2.6
= 2.6 in 1982 79 123.8
Bexley
1.6
7.6 in 1957 72 94.4
Berowra
5.5
6.6 in 1982 60 108.2
Rose Bay
3.8
12.2 in 2007 41 133.3



Summaries for the Sydney area

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

Summary statistics for May 2008
Maximum temperatures
for May
(°C)
Minimum temperatures
for May
(°C)
Rainfall
for May
(millimetres)
Mean for
May
2008
Diff
from
normal
Highest for
May
2008
Mean for
May
2008
Diff
from
normal
Lowest for
May
2008
Total for
May
2008
Normal
for
May
Rank of
May
2008
Fraction of
May
normal
Sydney (Observatory Hill) 20.5 +0.2 23.6 6th 11.4 -0.6 8.8 18th 3.0 121.5 lowest on record 2%
Liverpool 21.2 +0.7 24.0 15th 7.0 -2.3 3.8 25th 5.6 68.8 very low 7%
Parramatta 20.7 +0.1 23.8 15th 8.5 -1.6 5.3 23rd 5.2 73.0 very low 7%
Prospect Dam 20.5 +0.3 23.2 6th 8.1 -2.0 4.5 18th 3.8 73.0 very low 5%
Richmond 20.5 +0.1 23.4 16th 5.5 -2.7 1.9 5th 2.8 58.3 very low 5%
Springwood* 19.0   22.4 16th 8.8   4.9 18th 2.8 73.9 very low 4%
Terrey Hills* 19.2   22.2 15th 9.8   5.3 18th 3.4

* 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 10am 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 - 2007 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