Wednesday 2 January 2008 - Monthly Climate Summary for Sydney extremes - Product code IDCKGC1xx0

Sydney has cool, wet and stormy December

 

Details

  • Cool, cloudy days with well below average maximum temperatures
  • Mild nights with above average minimum temperatures
  • Persistent warm nights, 19 nights with minimum temperature above 18°C (normally 14 nights above 18°C)
  • Well above average rainfall
  • Stormy month, highest number of thunderstorms for December since 1959
  • Below average sunshine

 

Rainfall

The total December rainfall of 123.2 mm at Sydney Observatory Hill was well above the historic December average1 of 77.7 mm.  It was the wettest December since 1992 (when 202 mm was recorded). There were 18 rain days during the month, well above the December average of 11 rain days, and the highest number since 1992. Unlike previous months, the heavy rain was not restricted to coastal suburbs with the inner-west also receiving significant falls. The highest totals were recorded in the inner-west and the northern suburbs where thunderstorms were most active. The lowest falls were in the south-east. Monthly totals ranged from 238.6 mm at Turramurra in the north to a low of 72 mm at Sans Souci in the south. Both Parramatta and Riverview recorded their wettest December since 1970.

Persistent high-pressure systems near Tasmania for most of the month caused prevailing moist E to SE airstreams on the NSW coast including Sydney. The persistent high humidity combined with slow moving low-pressure troughs and cold, unstable air in the upper atmosphere produced the above average rainfall in the Sydney area during December.

The Warragamba Dam catchment received moderate rainfall during December contributing to the slow but steady rise in storage levels. Monthly totals over the entire catchment were generally in the 70 - 120 mm 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

Daytime temperatures in Sydney were quite cool during December. The average maximum temperature at Observatory Hill was 24.7°C, which is almost 1°C below the historic average1 temperature of 25.6°C. Cool, cloudy days persisted for most of the month with prevailing SE winds. It was slightly warmer in the western suburbs with an average maximum temperature at Richmond of 26.4°C. However, this is below the historic December average by 2.6°C and one of the lowest average maximum temperatures on record at Richmond for December. The main moderating effect on temperatures were the frequent cloudy days and persistent onshore winds for most of the month. Winds were between NE to SE for 50−60% of the time along the coast.

Night-time temperatures were above the historic average over the whole Sydney metropolitan area during December .  The average minimum temperature of 18.5°C at Observatory Hill was 0.5°C above the historic December average1. Nights were persistently warm with 19 nights when the temperature did not fall below 18°C at Observatory Hill. Normally Sydney would expect 14 nights above 18°C. Although average minimum temperatures were about 2°C cooler in far western suburbs they were still above the historic December average at all inland sites.

The highest temperature at Sydney (Observatory Hill) during December was a mild 30.2°C on the 4th while the lowest overnight temperature was 14.8°C on the 14th. Corresponding extremes in the Sydney metropolitan area ranged from a daytime high of 33.7°C at Penrith Lakes on the 21st to an overnight low of 9.7°C at Campbelltown on the 26th.

Wind

The prevailing direction along coastal Sydney was between NE to SE for 50−60% of the time. The highest wind gust recorded was 72 km/h at Badgerys Creek on the 7th.

Other phenomena

A total of 7thunderstorms occurred in Sydney during December, the highest number since 1959 when 11storms were recorded. The historic average is only 4 storms. Heavy downpours with storms early in the month caused local flash flooding in the inner west, Liverpool and northern beaches. A supercell thunderstorm on 9 December produced heavy rain, squally winds and giant hail up to 7cm size from Blacktown to Wahroonga with unconfirmed reports of 11cm size hail in Cherrybrook. The total damage bill was close to $200 million.

Associated with the above average rainfall and moist SE winds was the high daytime humidity. The average relative humidity at 3pm was 62% which is the highest recorded in December since 1992. The historic average at this time is 59%.

The amount of sunshine in Sydney varied considerably from week to week with periods of clear, sunny weather followed by cloudy, showery spells. The average daily sunshine during December was 6.9 hours per day, well below the historic average of 8.0 hours per day.

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 for the Sydney area

Hottest day
Highest temperature
33.7°C at Penrith Lakes on the 21st
Warmest days on average
Highest mean daily maximum temperature
26.8°C at Penrith Lakes
Coolest days on average
Lowest mean daily maximum temperature
23.9°C at Terrey Hills
Coldest day
Lowest daily maximum temperature
17.0°C at Springwood on the 11th
Coldest night
Lowest temperature
9.7°C at Campbelltown on the 26th
Coolest nights on average
Lowest mean daily minimum temperature
15.1°C at Campbelltown
Warmest nights on average
Highest mean daily minimum temperature
18.6°C at Sydney Airport
Warmest night
Highest daily minimum temperature
22.7°C at Bankstown Airport on the 22nd
Wettest overall
Highest total rainfall
238.6 mm at Turramurra
Driest overall
Lowest total rainfall
72.0 mm at Sans Souci
Wettest day
Highest daily rainfall
82.0 mm at North Rocks on the 6th
Highest wind gust
72 km/h at Badgerys Creek on the 7th

 

Summaries for the Sydney area

Summary statistics for December 2007
Maximum temperatures
for December
(°C)
Minimum temperatures
for December
(°C)
Rainfall
for December
(millimetres)
Mean for
December
2007
Diff
from
normal
Highest December
2007
Mean for
December
2007
Diff
from
normal
Lowest for
December
2007
Total for
December
2007
Normal
for
December
Rank of
December
2007
Fraction of
December
normal
Sydney (Observatory Hill)
24.7
−0.9 30.2 4th
18.5
+0.5 14.8 14th 123.2 77.7 high 158%
Camden Airport
26.2
−2.3 31.9 21st
15.8
+0.7 10.0 14th 93.4 52.4 very high 178%
Parramatta
25.7
−1.8 32.3 21st
16.6
+0.4 12.0 23rd 166.3 68.4 very high 244%
Richmond
26.4
−2.6 33.0 21st
16.7
+0.5 11.6 23rd 117.2 70.3 high 167%
Springwood
24.4
30.5 4th
15.2
11.9 14th 119.6 101.5 normal 118%
Terrey Hills
23.9
29.2 21st
16.6
13.0 13th 160.4

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

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

December 2007

Normal for December

Number of rain days

18
11

Average sunshine (hours per day)*

6.9
8.0

Average humidity at 3pm (%)

62
59

Number of thunderstorms

7
4

Number of windy days*

4
7
Number of gale days*
0
1

* recorded at Sydney Airport


Notes

This statement has been prepared based on information available at 12 pm on Wednesday 2 January 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 - 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.