Wednesday, 1 August 2007 - Monthly Climate Summary for Sydney extremes - Product code IDCKGC1xx0

Coldest July in Sydney for 9 years

Summary

  • Average temperatures very close to historic averages
  • However, average maximum temperature lowest since 1998
  • Rainfall below average
  • Frosty nights in western suburbs
  • Windy along coast, 6 windy days recorded
  • Sunny month with above average sunshine hours

Rainfall

The total July rainfall of 67.2 mm at Sydney Observatory Hill was below the historic July average1 of 97.6 mm. Although the monthly total is only 69% of the average it still falls within the normal range of variability for July totals. Practically the whole month's rainfall occurred on 2 days, the 9th and 10th, when a low pressure system passed over Sydney.  Very little rain occurred over the remainder of the month with high pressure systems dominating the Sydney region.  There were 8 rain days during the month, below the historic average of 10 rain days. Rainfall distribution over the Sydney area for July was highest in parts of the eastern and northern suburbs and lowest in the western suburbs with well below average totals in the far west. Totals ranged from 67.2 mm at Sydney Observatory Hill to 12.0 mm at Springwood in the lower Blue Mountains. See Sydney rainfall distribution map.

Despite the below average rainfall over Sydney and much of NSW in July, computer models (current as of 1st August 2007) are still predicting moderate cooling of the central and eastern tropical Pacific Ocean in the next month or two, and a moderate chance of a La Niņa occurring in 2007. Even if La Niņa thresholds are not met, cooler than average waters in the central to eastern Pacific are usually associated with average to wetter than average seasons over eastern and northern Australia, especially if accompanied by positive SOI values. More information and updates on La Niņa can be found at the Bureau's ENSO Wrap-up page.

The Warragamba Dam catchment received only light rainfall during July, however, supply levels continued to increase slowly.  Monthly totals over the catchment were generally in the 10−20 mm range, significantly below the historic July average of 40−50 mm.  Recent rainfall in Sydney's catchments can be found on the Sydney Catchment Authority web site at: http://www.sca.nsw.gov.au/dams/rainfall.html.

Temperatures

The average maximum (daytime) temperature at Observatory Hill was 17.1°C, which is equal to the historic average1.  Although temperatures were average, it is still the lowest average maximum for July since 1998 (when 16.2°C).  The elevated locations of Springwood (362 metres) and Terrey Hills (199 metres) recorded slightly cooler daytime temperatures.

Night-time temperatures were close to average along the coast but below average in the far west. The average minimum at Sydney (Observatory Hill) of 8.5°C was 0.1°C above the historic1 July average. However, minimum temperatures were more than 5°C lower in far western suburbs, averaging 3.2°C at Richmond. Extended periods of frost were recorded in low-lying parts of the western suburbs, especially from 12th to 19th July.  Liverpool recorded 13 frosts during the month compared to an average of 7 frosts for July.

The highest temperature at Sydney (Observatory Hill) during July was 23.4°C on the 26th while the lowest temperature was 3.7°C on the 17th.  This is the lowest temperature recorded at the Observatory Hill site in 21 years (since 3.1°C in July 1986).  Corresponding extremes in the Sydney area ranged from 23.8°C at Sydney Olympic Park and Parramatta on the 3rd to −3.5°C at Badgerys Creek on the 17th.

Although coastal Sydney recorded close to average temperatures in July, several factors have made it seem colder, including a series of mild Julys in recent years. Since 1999 every July has recorded an average maximum temperature between about half and 2°C above the historic average.  This period also includes Sydney's warmest July on record (2005) as well as its 3rd and 4th warmest Julys (2002 and 2000).  Other factors include a higher than usual number of windy days (see wind section below).

For the winter season so far (1 June to 31 July), Sydney has had its coldest start to winter since 1989. The average maximum temperature for the 2 month period is 16.9°C, the lowest since 1989 when 16.5°C was recorded. The historic average maximum for the 2 month period is 17.4°C.

Some sites had their lowest July temperature on record.

Wind

Sydney experienced quite windy conditions in July, especially along the coast, with 6 windy days recorded (average speed 40−62 km/hr), compared with an average of 4 windy days.  The highest wind gust in the Sydney area was 91 km/hr at Sydney Airport on the 5th.  The prevailing direction during the month was NW to SW with about 77% of all winds within this quadrant. Normally Sydney would expect less than 60% of winds from this direction. The prevailing westerlies contributed toward the dry conditions experienced in the Sydney area during July.

Other phenomena

Generally sunny conditions prevailed during July with sunshine averaging 7.2 hours per day compared to the historic average for July is 6.6 hours per day. There were two thunderstorms during the month (historic average 1storm), one producing small hail on the 9th.

Further information

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


Extremes for the Sydney area

Hottest day
Highest temperature
23.8°C at Parramatta and Sydney Olympic Park on the 3rd
Warmest days on average
Highest mean daily maximum temperature
17.3°C at Sydney Olympic Park
Coolest days on average
Lowest mean daily maximum temperature
15.4°C at Terrey Hills
Coldest day
Lowest daily maximum temperature
11.8°C at Terrey Hills on the 8th
Coldest night
Lowest temperature
−3.5°C at Badgerys Creek on the 17th
Coolest nights on average
Lowest mean daily minimum temperature
2.9°C at Campbelltown (Mount Annan)
Warmest nights on average
Highest mean daily minimum temperature
8.5°C at Sydney (Observatory Hill)
Warmest night
Highest daily minimum temperature
13.9°C at Sydney (Observatory Hill) on the 4th
Wettest overall
Highest total rainfall
67.2 mm at Sydney (Observatory Hill)
Driest overall
Lowest total rainfall
12.0 mm at Springwood
Wettest day
Highest daily rainfall
43.8 mm at Riverview on the 9th
Highest wind gust
91 km/h at Sydney Airport on the 5th

Records for the Sydney area

Record lowest July temperature
Lowest temperature
in July 2007 (°C)
Previous lowest
for July
Years of
record
Normal for
July
Prospect Dam −0.6 on the 17th 0.0 on the 16th in 1978

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Summaries for the Sydney area

Summary statistics for July 2007
Maximum temperatures
for July
(°C)
Minimum temperatures
for July
(°C)
Rainfall
for July
(millimetres)
Mean for
July
2007
Diff
from
normal
Highest for
July
2007
Mean for
July
2007
Diff
from
normal
Lowest for
July
2007
Total for
July
2007
Normal
for
July
Rank of
July
2007
Fraction of
July
normal
Sydney (Observatory Hill) 17.1 0.0 23.4 26th 8.5 +0.1 3.7 17th 67.2 97.6 normal 69%
Parramatta 17.1 −0.2 23.8 3rd 6.2 0.0 0.0 17th 35.8 45.9 normal 79%
Richmond 17.0 −0.3 22.7 3rd 3.2 −0.3 −3.4 17th 20.8 35.9 low 58%

Liverpool

17.1

−0.2

23.4

26th

3.4

−1.3

−2.6

17th

31.2

40.1

normal

78%

Springwood* 15.6 21.6 26th 4.9 −2.6 17th 12.0 58.0 low 21%
Terrey Hills* 15.4 21.6 3rd 6.8 0.2 17th 42.0

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

Additional climate data for Sydney (Observatory Hill) for July 2007
 

July 2007

Normal for July

Number of rain days

 8

 10

Average sunshine hours per day*

 7.2

6.6

Average humidity at 3pm (%)

 47

52

Number of thunderstorms

2

1

Number of windy days*

6

4

* recorded at Sydney Airport


Notes

This statement has been prepared based on information available at noon on Wednesday 1 August 2007. The data has been quality controlled, 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 Liverpool 1962 - 2006.  Rainfall averages and extremes for Observatory Hill are based on all years of record 1859 - 2006.

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.