Tuesday 1 May 2007 - Monthly Climate Summary for Sydney - Product code IDCKGC15L0

Sydney has cool, wet April

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Main points:

Temperature

Although much of NSW recorded above average temperatures during April, the Sydney area experienced cool conditions with below average temperatures.  This was due to a combination of above average rainfall and persistent, cool S-SE winds.  The average maximum (daytime) temperature at Observatory Hill was 23.0°C, or 0.2°C below the historic average¹of  23.2°C.  Slightly cooler days were experienced in the western suburbs where average maximum temperatures were about 1°C lower than coastal suburbs. The average maximum temperature at Richmond of 22.5°C was the 7th lowest for April since records commenced in 1929.

The highest temperature at Sydney (Observatory Hill) during April was 27.1°C on the 11th while the lowest temperature was 12.6°C on the 26th.   The lowest maximum temperature was 17.3°C on the 25th, which is the lowest for April in 8 years and the coldest Anzac Day since 1948.  Corresponding extremes in the Sydney area ranged from 30.4°C at Sydney Olympic Park on the 15th to 6.3°C at Camden Airport on the 11th.

Rainfall

The total April rainfall of 179.6 mm at Sydney Observatory Hill was well above the historic April average of 125.7 mm.  There were 12 rain days which is average for April.   Rainfall totals varied greatly over the Metropolitan area during the month with heavy rain falling along the coast while western suburbs recorded only light falls. Monthly totals were highest in the eastern suburbs with Rose Bay recording a total of 386.8 mm, its wettest April since 1988.  In the west the lowest April total was only 32 mm at St Clair.  The two major rain events during April (4th to 8th and 23rd to 25th) were caused by moist on-shore S-SE air streams and cold air in the upper atmosphere.  Typically with S-SE air flows, the associated rainfall does not penetrate very far inland and this was the case in this instance.

Unfortunately the rain also failed to reach the Warragamba catchment with monthly totals over much of the catchment around 20 to 40 mm.   However, the smaller Woronora catchment to the south of Sydney and closer to the coast recorded quite heavy rain during April with a total of 195 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

Other phenomena

Three thunderstorms were recorded over Sydney metropolitan area during April with 2 storms at the official site at Sydney Observatory Hill (historic average 1storm). Slow moving thunderstorms with heavy rain affected the eastern suburbs on the 4th and 22nd causing local flash flooding, especially in the Double Bay area where shops and houses were damaged by floodwaters.  At Rose Bay, 98 mm was recorded on the 22nd, which included 42 mm in 30 minutes. This intensity has a recurrence interval of around 10 years.  A similar slow moving thunderstorm at Rose Bay on the 4th produced 96 mm in less than 3 hours.  A combination of plentiful moisture from S-SE winds and an upper low pressure trough contributed toward the severe thunderstorms.  Sunshine averaged 6.6 hours per day which is below the April average of 6.9 hours per day and a marked contrast with April last year which was the sunniest on record (averaging 9.3 hours per day).  A dense fog in the early hours of the 20th reduced visibility in the CBD area to 150 metres for several hours and only 100 metres at Sydney Airport and at Richmond.

Further information

Mike De Salis
NSW Climate Services Centre
Bureau of Meteorology
Phone (02) 9296 1542
Email reqnsw@bom.gov.au

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Extremes for the Sydney area

Hottest day Highest temperature	30.4°C at Sydney Olympic Park on the 15th
Warmest days on average Highest mean daily maximum temperature	24.4°C at Penrith
Coolest days on average Lowest mean daily maximum temperature	21.8°C at Terrey Hills
Coldest day Lowest daily maximum temperature	16.1°C at Springwood on the 25th
Coldest night Lowest temperature	6.3°C at Camden Airport on the 11th
Coolest nights on average Lowest mean daily minimum temperature	11.2°C at Camden Airport
Warmest nights on average Highest mean daily minimum temperature	15.6°C at Sydney (Observatory Hill) and Sydney Airport
Warmest night Highest daily minimum temperature	18.6°C at Sydney Airport on the 12th
Wettest overall Highest total rainfall	386.8 mm at Rose Bay (wettest April since 1988)
Driest overall Lowest total rainfall	32.0 mm at St Clair
Wettest day Highest daily rainfall	98.0 mm at Rose Bay for 24 hours to 9am on 23rd
Highest wind gust	67 km/h at Sydney Airport on the 6th

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Summaries

Summary statistics for the Sydney area for April 2007
	Maximum temperatures April 2007 (°C)				Minimum temperatures April 2007 (°C)				Rainfall April 2007 (millimetres)
	Mean for April	Diff from normal	Highest for April		Mean for April	Diff from normal	Lowest for April		Total for April	Normal for April	Rank of April	Fraction of April normal
Sydney (Observatory Hill)	23.0	−0.2	27.1	11th	15.6	+0.4	12.6	26th	179.6	125.7	high	143%
Parramatta	23.4	−0.5	29.1	15th	13.2	+0.4	10.5	13th	115.9	85.1	high	136%
Richmond	22.5	−1.6	27.4	15th	11.3	−0.8	8.0	11th	56.6	70.3	normal	81%
Camden	23.5	−0.7	28.2	15th	11.2	−0.2	6.3	11th	36.8	54.1	normal	69%
Terrey Hills*	21.8		26.8	15th	13.9		10.8	26th	137.0
Springwood*	21.9		26.2	5th	11.9		9.0	11th	44.2	73.8	normal	59%

Summary phenomena for Sydney (Observatory Hill) for April
	April 2007	Normal for April
Number of rain days	12	12
Average sunshine hours per day*	6.6	6.9
Average humidity at 3pm (%)	63	59
Number of thunderstorms	2	1
Number of windy days*	2	3

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Notes

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