Friday, 1 August 2008 - Monthly Climate Summary for Sydney extreme rainfall - Product code IDCKGC15x0

Sydney during July: mild along coast, cold, dry inland

Summary

  • Slightly above average temperatures along coast, below average inland
  • Average rainfall along coast, below average inland
  • Partly cloudy month with slightly below average sunshine
  • Frosty mornings inland suburbs

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Rainfall

Although there was close to average rainfall along coastal Sydney during July, western suburbs recorded well below average totals. At Observatory Hill the total of 89.6 mm was only a few millimetres below the historic July average1 of 97.6 mm. There were 12 rain days during July which is a little above the July average of 10 days. Most of Sydney's rain fell during the last week of the month when two separate low pressure systems in the northern Tasman Sea directed moist south-east airstreams onto the NSW coast.

The wettest suburbs were in coastal Sydney where Randwick recorded 145.2 mm for the month. Rose Bay recorded Sydney's wettest day for the month with 70.6 mm on the 29th. However, the heavy coastal showers failed to penetrate inland with only light falls in the west. The lowest total for July was only 10.0 mm at Glenmore Park, near Penrith.

Only light rainfall was recorded over the Warragamba Dam catchment during July. The entire catchment recorded between 20 and 40 mm during the month which is below the historical July average. This contributed towards a very slow decline in storage levels during 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.

Temperature

July was a cool to cold month across the Sydney basin with both the maximum and minimum temperatures below the historic averages for all areas except the coastal sites of Observatory Hill and Sydney airport. The average maximum temperature at Observatory Hill of 17.2 °C was 0.9°C above the historic July average1. This is now the 10th consecutive July with above average maximum temperatures at Observatory Hill.

Sydney's nights were cool during July, the average minimum temperature at Observatory Hill was 8.3°C which is 0.3°C above the historic July average 1. This is the lowest average minimum temperature for July since 2002 (when 7.9°C). The western suburbs experienced much colder nights due to the clear, calm conditions which favour the development of frosts under the stabilising influence of slow-moving high pressure systems during the month. There were 14 frosts recorded at Richmond during the month, close to the historic average of 13 frosts for July.

A very cold, wet and windy day on the 28th caused the apparent (wind chill) temperature to fall to a very cold −1°C at Sydney Airport at 5pm, one of the few times the apparent temperature has fallen below zero in coastal Sydney.

Wind

There were 8 windy days2 in coastal Sydney during July, twice the normal number of 4 windy days. Sydney experienced a dominance of winds from the W-NW during the mornings with over 80% of all winds from this direction, compared to the normal frequency of about 70% for this time of year. The highest wind gust in the greater Sydney area was 81 km/hr at Sydney Airport on the 1st. However, the more exposed coastal site at Wattamolla in the Royal National Park south of Sydney, recorded a wind gust of 98 km/hr on the 28th.

Other phenomena

Sunshine hours averaged 6.5 hours per day which is slightly below the normal Sydney sunshine of 6.6 hours per day. Fog was recorded over parts of the metropolitan area on the 15th but none recorded in the city or at the airport during July. A thunderstorm on the 27th caused heavy soft hail in various suburbs including Bankstown, Concord, Chatswood and Killara. Cold air from the hailstorm dropped the 3.30pm temperature to 7.7°C at Bankstown, the lowest on record at this time for that site.

Further information

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

2 Windy day defined as average wind speed of 40 km/hr or more at observation time.

Extremes for the Sydney area

Warmest day
Highest temperature		 23.1°C at Sydney (Observatory Hill) on the 14th
Warmest days on average
Highest mean daily maximum temperature		 17.5°C at Sydney Olympic Park AWS
Coolest days on average
Lowest mean daily maximum temperature		 15.3°C at Springwood
Coldest day
Lowest daily maximum temperature		 11.5°C at Springwood on the 28th
Coldest night
Lowest temperature		 −2.5°C at Richmond RAAF AWS on the 12th
Coolest nights on average
Lowest mean daily minimum temperature		 2.6°C at Richmond RAAF AWS
Warmest nights on average
Highest mean daily minimum temperature		 8.3°C at Sydney (Observatory Hill)
Warmest night
Highest daily minimum temperature		 10.8°C at Sydney (Observatory Hill) on the 2nd and 20th and at Terrey Hills AWS on the 14th
Wettest overall
Highest total rainfall

145.2 mm at Randwick

Driest overall
Lowest total rainfall		 10.0 mm at Glenmore Park
Wettest day
Highest daily rainfall

70.6 mm at Rose Bay on the 29th
Highest wind gust

98 km/h at Wattamolla on 28th
81 km/h at Sydney Airport AWS on the 1st

AWS = Automatic Weather Station

 

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 July 2008
Maximum temperatures
for July
(°C)		 Minimum temperatures
for July
(°C)		 Rainfall
for July
(millimetres)
Mean for
July
2008		 Diff
from
normal		 Highest for
July
2008		 Mean for
July
2008		 Diff
from
normal		 Lowest for
July
2008		 Total for
July
2008		 Normal
for
July		 Rank of
July
2008		 Fraction of
July
normal
Sydney (Observatory Hill) 17.2 +0.9 23.1 14th 8.3 +0.3 5.5 23rd 89.6 97.6 normal 92%
Bankstown Airport AWS 16.7 −0.5 21.7 14th 4.5 −0.6 1.0 12th 61.2 43.5 high 141%
Camden Airport AWS 16.8 −0.4 20.5 14th 2.7 −0.2 −2.2 23rd 21.6 39.7 normal 54%
Parramatta 17.3 normal 22.1 14th 5.4 −0.8 2.3 22nd 38.8 45.7 normal 85%
Penrith Lakes AWS 17.0 −0.7 21.5 14th 4.8 −0.6 0.3 23rd 16.6 50.8 low 33%
Prospect Reservoir 16.6 −0.2 21.2 14th 5.4 −0.6 1.5 12th 31.4 57.4 normal 55%
Richmond RAAF 17.0 −0.5 22.0 14th 2.6 −0.9 −2.5 12th 10.2 35.9 low 28%
Springwood* 15.3   20.7 14th 5.9   2.4 12th 17.4 57.3 low 30%
Terrey Hills AWS* 15.5   19.9 14th 7.0   2.9 12th 70.0

* 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 10am on Friday 1 August 2008. Some checks have been made on the data, but it is possible that results will change as new information becomes available.

1Averages:  historic rainfall and temperature averages are based on all available data.

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 reqnsw@bom.gov.au