Wednesday 1 November 2006

SYDNEY MONTHLY CLIMATE SUMMARY - NSW REGIONAL OFFICE

Very warm and dry in Sydney during October

October 2006 - Main Points:

• 8th warmest October on record with average temperature of 19.4°C.
• Average maximum temperature of 24.2°C was 6th highest on record.
• Well below average rainfall, total of 17.2mm was 16th driest October.
• 2 consecutive days when temperature exceeded 36°C, last occurred in October in 1926.
• 4 days over 30°C, average 2 days.
• Close to average sunshine with 8.1 hrs/day.
• Windy month along coast with 12 strong wind days (average 6).

Temperatures:   Well above average temperatures were recorded in Sydney during October with now 9 of the last 10 years having above average October temperatures.  The average monthly mean temperature (the average of the daily maximum and minimum temperatures) of 19.4°C was more than 1°C above the historic average¹ of 18.2°C and ranks as 8th warmest October since records commenced in 1859.  The warmer than average conditions are consistent with global rising temperatures and enhanced by the emerging El Nino event.

Days were particularly warm, especially during the first half of the month when maximum temperatures reached the mid-twenties to mid thirties.  Milder conditions prevailed during the second half of the month with temperatures much closer to or even slightly below average.  The average maximum daytime temperature of 24.2°C at Observatory Hill was 2°C above the historic average¹ of 22.2°C and the 6th highest ever recorded for October.

A significant early spring heat wave on the 13th and 14th with consecutive days over 36°C was a very rare event for October and is unusual even for summer. This is only the second time since 1859 that such a severe heatwave has occurred in October, the last time was in 1926.   Observatory Hill recorded 4 hot days during the month (temperature exceeding 30°C), twice the historic average of 2 hot days.  The unseasonally warm conditions earlier in the month were caused by a series of intense low-pressure systems near Tasmania and a blocking high-pressure system in the Tasman Sea directing persistent warm to hot and dry N-NW winds over Sydney.  Frequent southerly changes contributed towards cooler weather later in the month.  The changeable conditions are expected during spring with the transition period between winter and summer seasons.

Nights were also mild with the average minimum temperature at Observatory Hill of 14.6°C, being slightly above the historic average¹ of 14.1°C.   However, nights were progressively cooler in suburbs further from the coast with Richmond recording an average minimum of 10.5°C, which is nearly 1°C below the historic average.

The highest maximum temperature at Sydney (Observatory Hill) during October was 36.7°C on the 13th, the 6th highest temperature ever recorded in October.  The lowest minimum temperature was 9.5°C on the 29th, which was also the lowest temperature this late in the season since 1964.   Corresponding extremes across the Sydney metropolitan area ranged from 37.8°C at Penrith on both the 13th and 14th to a low of 2.3°C at Camden on the 29th.

Rainfall:    The total rainfall of only 17.2mm was well below the historic average of 78mm and ranks as 16th driest October since records commenced in 1859.   There were only 6 rain days during the month which is well below the historic average of 11 rain days.  Similar dry conditions prevailed throughout the Metro area and over the Sydney water catchments.  Metropolitan rainfall for October ranged from 22.6mm at Cronulla in Sydney's south to only 1mm at Willmot in the far west.  The lack of rain is consistent with an emerging El Nino event and persistent high pressure over Sydney.

Rainfall - Warragamba catchment:  Rainfall over the catchment area was exceptionally low during October. Except for Katoomba on the eastern edge of the Warragamba catchment, all stations within the catchment area recorded less than 8mm with parts of the upper catchment near Goulburn recording a rainless month.  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

Other phenomena:    Sydney averaged 8.1 hours of sunshine per day during October which is close to the historic average of 7.9 hrs/day.   There was only one thunderstorm during the month (historic average 2 storms).  Winds were stronger than usual along the coast with fresh NE sea-breezes and numerous southerly changes, especially during the second half of the month.  Twelve windy days were recorded at Sydney Airport compared to an historic average of 6 windy days for October. Wind speed decreased significantly away from the coast with only one or two windy days recorded in inland suburbs where southerly changes and sea-breezes failed to penetrate.  Sydney's average air pressure at 9am was well above the historic average and the highest since 1963.  This is consistent with a persistent high pressure ridge over Sydney and NSW during October.

Sydney Observatory Hill   (Elev 39m)

October 2006

Historic average¹

October 2005

 24.2

 22.2

 24.3

 14.6

 14.1

 15.8

 19.4

 18.2

 20.1

 17.2

   77.7#

 43.0

 6

11

 12

 8.1

7.9

 7.1

Average relative humidity at 3pm (%)

 54

56

 56

Number of days of thunderstorms

 1

2

 1

Number of windy days*

 12

6

 7

  Parramatta

(Elev 55m)

   Richmond  

(Elev 19m)

     Camden    
 (Elev 79m)

Terrey  Hills #
(Elev 199m)

Springwood #

(Elev 362m)

October 2006

Historic average¹

October 2006

Historic average¹

October 2006

Historic average¹

October 2006

October 2006

 25.3

 23.8

 26.3

 24.4

 26.1

 23.9

 23.1

 24.7

 12.4

 11.9

 10.5

 11.2

 9.7

 9.9

 12.9

 10.6

 18.8

 17.8

 18.4

 17.8

 18.0

 16.9

 18.0

 17.6

8.2

 71.3

 12.8

 64.1

 5.4

 70.3

 18.4

 18.2

 4

 10

 1

 10

 3

 10

 7

 5

October 2006

All years

October 2006

All years

October 2006

All years

October 2006

October 2006

 36.7 
(13th)

  38.2   (2004)

 37.2
 (13th)

40.1  (1988)

36.6
 (14th)

40.4  (1988)

  35.4
 (14th)

 35.6
(13th

9.5
 (29th) 

  5.7   (1927)

 6.2
(23rd)

3.6  (1998)

3.8
 (23rd) 

1.7  (1931)

 7.5
(29th)

 4.7
(29th)

16.3
(21st)

  12.1   (1871)

  16.0
 (21st)

13.1  (1967)

15.8
 (16th) 

13.7  (1967)

  15.2
 (21st)

  13.2
(21st)

 8.2
(16th)

161.8  (1902)

 4.2
(22nd)

106.5  (1987)

82.8  (1954)

 10.0
 (16th)

  14.4
(16th)

SSW
@ 87  
(8th)*

WSW @ 113  (1957)

-

 WNW
@ 72
 (18th)

  NW @ 115 (1983)

 S @ 63  (8th)

-

This statement has been prepared based on information available at noon on 01/11/06. Although every effort has been made to check the data, it is possible that some figures 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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