Thursday, 1 November 2007 - Monthly Climate Summary for Sydney extremes - Product code IDCKGC1xx0

Warm nights and dry, sunny days in Sydney during October

Summary

Rainfall

The total October rainfall of 27.0 mm at Sydney Observatory Hill was well below the historic October average1 of 77.0 mm.  There were only 5 rain days during the month, also below the October average of 11 rain days.   Monthly rainfall totals were below average over the entire metropolitan area with the lowest in the western suburbs, particularly the south-west. Totals ranged from 49 mm at Merrylands West to only 11.2 mm at Camden Airport.  Much of the rainfall occurred during thunderstorms caused by the passage of several low-pressure troughs.   Thunderstorms were most active in the Parramatta, inner west and North Shore suburbs where some localised heavy falls and flash flooding occurred. At Merrylands West 36mm was recorded in about 15 minutes on the 26th.

The Warragamba Dam catchment received only light rainfall during October, with storage levels falling slowly. Monthly totals over the catchment were generally in the 15-30mm range. 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

The average maximum (daytime) temperature at Observatory Hill was 25.0C, which is well above the historic average1 temperature of 22.2C.  This is the 3rd highest average maximum temperature on record for October and the highest since 1988 (when Sydney recorded its hottest October on record).  It was even warmer in the western suburbs with an average maximum temperature at Richmond of 27.4C (3.0C above the historic average).   Sydney experienced several days of hot weather caused mainly by brief spells of hot NW winds.  There were 5 days when the temperature exceeded 30C at Observatory Hill, the highest number since 1988. Normally Sydney would expect 2 days over 30C in October.

Over the last 10 years, there has been nine Octobers with above average maximum temperatures and only one below average.

Night-time temperatures were very mild along the coast but cooler over inland suburbs.  The average minimum temperature of 15.7C at Observatory Hill was 1.6C above the historic October average1 and the 3rd highest on record (records since 1859).  However, minimum temperatures were several degrees cooler in far western suburbs and up to 6C cooler at Camden. The average at Camden (9.5C) was slightly below the historic October average.

Coastal Sydney experienced many mild to warm nights - at Observatory Hill there were 17 nights when the temperature did not fall below 16C, a record for October. The previous highest was 15 nights above 16C in October 2005 (records from 1859).  Normally Sydney would expect 7 nights above 16C in October.  On the 29th, the warmest night of the month, the minimum temperature at Observatory Hill was 21.3C or more than 7C above average.  The highest minimum temperature in the metropolitan area during October was 21.6C at Parramatta and Sydney Airport on the 29th;   the warm conditions on this night were caused by heavy cloud cover and moderate northerly winds.

The highest temperature at Sydney (Observatory Hill) during October was 34.8C on the 3rd while the lowest temperature was 10.5C on the 13th. Corresponding extremes in the Sydney metropolitan area ranged from 36.2C at Sydney Airport on the 13th to 3.4C at Camden on the 5th.

Some sites had their highest October mean daily maximum temperature on record.

Wind

There were 11 windy days as measured at Sydney Airport, compared to an average of 6.  The highest wind gust recorded was 89 km/h at Sydney Airport on the 3rd and 6th.  Except for brief spells of warm westerly winds, the prevailing direction was between E and S.

Other phenomena

There were 5 days with thunderstorms in Sydney during October compared to the historic average of only 2 storms.  There were 2 severe storms producing hail and flash flooding. On the 12th, 4cm size hail was reported at Camden Airport and 2cm hail at Heathcote. On the 26th, heavy rain, local flash flooding and power outages occurred in the Ryde area.

On several days during the month hot, dry westerly winds caused very low humidity levels in Sydney.  On the 3rd the humidity fell to a very dry 8%, the lowest reading in October since 1991 and one of the lowest ever recorded in October. Similar low humidity occurred on 1st, 16th and 29th.  Strong winds and high temperatures on these days created a very high bushfire danger with fires burning over 300 hectares of bushland in Ku-ring-gai Chase National Park and at Cowan in Sydney's north on the 2nd and 3rd. Sunshine was plentiful during October with an average of 8.9 hours per day, the highest since 2001.

Further information

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


Extremes in the Sydney area

Hottest day
Highest temperature
36.2 C at Sydney Airport on the 3rd
Warmest days on average
Highest mean daily maximum temperature
28.1 C at Penrith Lakes
Coolest days on average
Lowest mean daily maximum temperature
25.0 C at Sydney (Observatory Hill) and Terrey Hills
Coldest day
Lowest daily maximum temperature
16.5 C at Springwood on the 24th
Coldest night
Lowest temperature
3.4 C at Camden Airport on the 5th
Coolest nights on average
Lowest mean daily minimum temperature
9.5 C at Camden Airport
Warmest nights on average
Highest mean daily minimum temperature
15.7 C at Sydney (Observatory Hill)
Warmest night
Highest daily minimum temperature
21.6 C at Parramatta and Sydney Airport on the 29th
Wettest overall
Highest total rainfall
49.0 mm at Merrylands West
Driest overall
Lowest total rainfall
11.2 mm at Camden Airport AWS
Wettest day
Highest daily rainfall
37.0 mm at Merrylands West on the 27th
Highest wind gust
89 km/h at Sydney Airport on the 3rd and 6th

Records in the Sydney area

Record highest October mean daily maximum temperature
Mean daily maximum
temperature
for October 2007 (C)
Previous highest
for October
Years of
record
Normal for
October
Prospect Dam

27.2

27.1 in 1988

41 b

23.6

Riverview Observatory

25.8

25.4 in 1949

70

22.7



Summaries

Summary statistics for October 2007
Maximum temperatures
for October
(C)
Minimum temperatures
for October
(C)
Rainfall
for October
(millimetres)
Mean for
October
2007
Diff
from
normal
Highest for
October
2007
Mean for
October
2007
Diff
from
normal
Lowest for
October
2007
Total for
October
2007
Normal
for
October
Rank of
October
2007
Fraction of
October
normal
Sydney (Observatory Hill) 25.0 +2.8 34.8 3rd 15.7 +1.6 10.5 13th 27.0 77.0 low 35%
Camden Airport 27.2 +3.2 34.4 3rd   9.5 -0.4 3.4 5th 11.2 68.4 low 16%
Parramatta 27.0 +3.2 35.0 3rd 12.6 +0.7 6.1 13th 27.7 69.8 low 40%
Richmond 27.4 +3.0 34.7 3rd 11.4 +0.2 4.6 5th 17.6 64.1 low 27%
Springwood 26.0 33.4 22nd 11.1 4.8 14th 22.6 76.2 low 30%
Terrey Hills 25.0 34.0 3rd 13.7 7.2 13th 33.0

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

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

October 2007

Normal for October

Number of rain days

5

11

Average sunshine hours per day*

8.9

7.9

Average humidity at 3pm (%)

 51

56

Number of thunderstorms

 5

2

Number of windy days*

 11

6

* recorded at Sydney Airport


Notes

This statement has been prepared based on information available at 12 pm on Thursday, 1 November 2007. 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 - 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.