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

Warm nights and dry, sunny days in Sydney during October

Summary

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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.

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

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.