La Nina influences - Temperature and rainfall for Eastern Australia - September 2010

La Nina was dominating eastern Australia during the month of September and the relevant plots for temperature and rainfall are provided below:

Average maximum temperature anomaly

Cooler than normal days appear to be the trend for September. Other than for coastal New South Wales and Queensland, daily temperatures were 1C to 3C below average. Closer to the coast, temperatures were closer to the average.

At Blacktown where I live, maximum temperatures failed to reach 20C on 9 days. There were no 30C days when compared to 2009 and the maximum temperatures of 26 to 27.2C occurred between 24 and 28 of the month. When a comparison is made to the El Nino year of 2009, it is found that there have been no 30C days so far this season from 1 September to 8 October 2010. For the same period of 2009, there had been 5 such days. Further it has reached 27C at Blacktown on 3 days for the same period of 2010 but during the same period of 2009, there had been 9 such days.  

Average minimum temperature anomaly

Minimum night time temperatures were warmer than normal except for south west New South Wales where minimum night time temperatures were 0C to 2C below average. Cloud cover would have kept night time temperatures warmer than normal across a large region of eastern Australia.

Cooler than normal days and warmer than normal nights appear to be the trend for September 2010.


Across eastern Australia, average to above average rainfall occurred except for coastal areas north and south of Sydney. These areas experienced rainfall deficits of 25 to 50 mm below average for the month while the rest of the state of New South Wales was satisfactory. It is noted that cloud bands moving across Queensland during the month resulted in significant rainfalls. Rainfall anomalies reach up to 400 mm above average. There were rain events in Victoria including Southern New South Wales and Queensland. The regions affected are identified in the Rainfall Anomaly Plot.

Given that La Nina is now dominating the weather pattern, here in Blacktown, the first 8 days of October have been characterised by cooler, cloudy weather with regular showers. So far, it has rained on 5 out of 8 days. Friday 8/10/2010 turned out sunny but only after a cloudy morning. There were heavy showers Wednesday afternoon that delivered 8 to 10 mm but no storm so far for the month. Saturday morning has turned out cloudy with isolated showers. Hence the start of October here in Western Sydney is one of clouds, showers and cooler temperatures.

The relevant plots produced from the Bureau of Meteorology Land and Water site for temperature and rainfall are provided below.

Harley Pearman

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