Sydney Monthly Climate Summary: July 2006
Wet and cloudy July for coastal Sydney

Tuesday 1 August, 2006

In Brief

• Wettest July since 1999, total of 140.2 mm. However, below average rainfall in far western suburbs.
• 15 rain days, last exceeded in July 1950 (when 21 days).
• Above average temperatures.
• Cloudy month with below average sunshine, only 5.9 hours/day (lowest for 5 years).
• Coastal Sydney recorded 3 fogs, highest for July since 1950 (when 4 fogs).

Details

Rainfall:

Sydney's total rainfall of 140.2 mm was well above the historic average¹ of 97.5 mm and the wettest July since 1999 (when 182 mm was recorded).  There were 15 rain days during the month which was last equalled in 1984 and last exceeded in July 1950 (when 21 rain days). The historic average is 10 rain days. Much of the rain fell during the second half of the month with heavy showers and rain periods associated with a low-pressure trough over NSW and a moist SE air stream. However, the heavy rain was confined mainly to south-eastern coastal suburbs with much lighter falls extending to far western and northern suburbs where below average rainfall was recorded. Metropolitan rainfall for July ranged from 233.8 mm at Rose Bay in Sydney's east (the 3rd wettest July in 40 years of record) to only 18 mm at St Clair in Sydney's far west.

The wet July follows above average rainfall in June with a 2-month total of 317 mm, the highest for consecutive months at Observatory Hill since April-May 2003 (when 541 mm).

Warragamba catchment:  July rainfall totals over the catchment area were generally 40−60 mm, with isolated heavier totals of 80−100 mm at fringe locations of Katoomba and Bowral. Recent rainfall over Sydney's catchments can be found on the Sydney Catchment Authority web site http://www.sca.nsw.gov.au/dams/rainfall.html.

Temperatures:

Above average temperatures were recorded in Sydney during July, making it the 8th consecutive July with above average temperatures. The average monthly mean temperature (the average of the daily maximum and minimum temperatures) of 13.5°C was above the historic average¹ of 12.8°C and ranks as the 10th highest since records commenced in 1859. Days were cool to mild with the average maximum day-time temperature of 17.9°C at Observatory Hill being above the historic average of 17.1°C. The average maximum temperature at the more elevated locations of Terrey Hills and Springwood was about 2°C cooler.

Nights were cool to mild with the average minimum temperature at Observatory Hill being 9.1°C, which was also above the historic average of 8.4°C. However, nights were progressively cooler in suburbs further from the coast and particularly cold in the western suburbs during the first 2 weeks of July when Richmond's temperature fell to −3.3°C on the 9th, the lowest Metropolitan temperature for the month.

The highest temperature at Sydney (Observatory Hill) during July was 23.0°C on the 11th while the lowest was 5.8°C on the 9th. Corresponding extremes across the Sydney metropolitan area ranged from 23.7°C at Sydney Airport on the 11th to −3.3°C at Richmond on the 9th.

Other phenomena:

Generally cloudy conditions prevailed during the month with an average of 5.9 hours of sunshine per day, the cloudiest July since 2001 (when 5.0 hrs/day). Because of the rain and high humidity, there were more fogs than usual over the Metro area. Fog occurred in coastal locations on the 15th, 16th and 27th with widespread mist on the 23rd. This is the highest number of fogs in July since 1950 (when 4 fogs). The historic average for July is 1 fog. Visibility was reduced to 600 metres on the 16th, closing the airport for several hours, while during the early hours of the 27th visibility fell to 200 metres in the city area. Fog and low cloud was also frequent over higher parts of the Blue Mountains with Katoomba recording 11 fogs during July (historic average 3 fogs).   Lightning and distant thunder was reported on 4 days but no thunderstorms were recorded at the official site at Observatory Hill.

Sydney Observatory Hill   (Elev 39 m)

July 2006

Historic average

July 2005

 17.9

 17.1

 19.0

 9.1

 8.4

 9.3

 13.5

 12.8

 14.1

 140.2

97.5#

62.8

 15

10

 7

 5.9

6.6

7.7

Average relative humidity at 3pm (%)

 56

52

49

Number of thunderstorms

0

1

0

Number of windy days*

3

4

2

  Parramatta

(Elev 55 m)

   Richmond  

(Elev 19 m)

     Camden       (Elev 79 m)

Terrey  Hills # (Elev199 m)

Springwood #

(Elev 362 m)

July 2006

Historic average

July 2006

Historic average

July 2006

Historic average

July 2006

July 2006

 17.8

 17.3

 17.2

 17.3

 17.5

 17.1

 16.1

 15.9

 7.3

 6.2

 3.1

 3.5

 2.3

 2.5

 7.8

 5.5

 12.5

 11.7

 10.2

 10.4

 9.7

 9.8

 12.0

10.7

 64.1

 45.5

 31.0

 35.9

 29.0

 41.0

 71.2

 50.8

 14

 8

 14

 6

 11

 7

 15

 10

July 2006

All years

July 2006

All years

July 2006

All years

July 2006

July 2006

  23.0 (11th)

  25.9   (1990)

 23.2  (11th)

25.9  (1990)

23.1  (11th)

27.6  (1990)

 21.9  (11th)

 21.1 (11th)

5.8  (9th) 

  2.2   (1890)

 2.6

 (13th)

−1.0  (2002)

−3.3  (9th) 

−8.3  (1970)

 3.4  (9th)

 0.4 (13th)

13.4  (19th)

  7.7   (1868)

  13.5  (19th)

9.0  (1984)

12.7  (14th) 

7.6  (1957)

 10.4  (19th)

 11.2 (15th)

 36.6 (4th)

198.0  (1931)

 15.8 (25th)

138.4  (1988)

86.9  (1988)

 13.0  (25th)

 24.4 (25th)

SSW @ 70  (18th)*

SSW @ 109  (1931)

-

 W @ 63  (31th)

  NW @ 126 (1964)

 SW @ 57  (18th)

-

This statement has been prepared based on information available at noon on 01/08/06. Although every effort has been made to check them, it is possible that results may change as new information becomes available.

A note about deciles: Deciles are used to give an element (in this case rainfall or temperature) a ranking. Deciles are calculated by arranging the totals in ascending order (from lowest to highest) then splitting them into 10 equal groups (thus the groups are called deciles). The first group would be in decile range one, the second group in decile range two, etc up to the highest annual totals (highest 10 per cent) being in decile range 10.

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 - 2005 and Camden 1972 - 2005.  Rainfall averages and extremes for Observatory Hill are based on all years of record 1859 - 2005.

Further information: Contact Mike De Salis 02 9296 1542, email: reqnsw@bom.gov.au

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