FYI: Monthly Climate Summary for Canberra - September 2009

[Matthew Frawley <>]

The following is provided for the information of subscribers (and as an addition to the annual summary provided in the Annual Bird Report): http://www.bom.gov.au/climate/current/month/act/summary.shtml

Canberra has warm September with above average rainfall

• Slightly above average rainfall
• Above average maximum temperatures
• Above average minimum temperatures
• High frequency of NW winds.
• Sunny month, averaging 8.4 hours of sunshine per day

Rainfall

Canberra Airport recorded a total rainfall of 56.2 mm during the month, which is slightly above the historical average of 52.1 mm. It is the first time in 5 months that Canberra has recorded above average monthly rainfall. However, this is well below the wettest September of 151 mm set in 1978. The number of rain days was also slightly above average at 12 days (September average 10 days) but several of these rain days were less than 1 mm.

Several cold fronts passed over the ACT producing light showers. However, a strong cut-off low pressure system over southern NSW on the 22nd caused thunderstorms and moderate showers in the ACT, accounting for more than half of the total monthly rainfall at Canberra Airport. The storms were heaviest in northern suburbs where 51.4 mm was recorded at Nicholls for the 24 hours to 9am on 23rd, the wettest day in the ACT during the month.

Monthly totals for September in Canberra suburbs ranged from a high of 89.4 mm at Nicholls in the northern suburbs to a low of 48.6 mm at Kingston in the inner south. Higher falls occurred on the ACT ranges where Corin Dam recorded a monthly total of 165.6 mm.

Temperatures

The mean maximum (daytime) temperature at Canberra Airport was 17.4 °C, which is 1.2 °C above the historical September average of 16.2 °C. This ranks as the 14th warmest September in the 71 year record at Canberra. It is now the 12th consecutive September with above average maximum temperatures, the last 'cool' September occurring back in 1997. The highest daily maximum temperature was 25.2 °C on the 13th. Although temperatures exceeding 25 °C in Canberra normally occur only once in every 5 years on average, they have now occurred 4 times in the last 4 years.

Nights were generally mild, with the mean minimum temperatures at Canberra Airport of 4.3 °C, 1.1°C above the September historical average of 3.2 °C. This is the 13th warmest September for average minimum temperatures since records commenced in 1939. It is also the 15th consecutive September with above average monthly minimum temperatures; the last September with below average minimums was back in 1994. Canberra Airport recorded only 8 frosts during the month (minimum temperature below 2 °C) well below the normal 13 frosts for September, and the lowest since September 1998. The lowest temperature in Canberra suburbs was -2.5 °C at Tuggeranong AWS on the 6th.

Prevailing NW winds and the lack of any significant cool changes contributed towards the mild temperatures during September. An El Nino event is currently maturing in the equatorial Pacific Ocean. These events are usually (but not always) associated with above average temperatures in eastern Australia. Very high temperatures experienced throughout August and September are likely due to the current influence of El Nino combined with the background, long-term warming that has been observed across Australia since the start of last century.

Wind

The prevailing wind direction over Canberra during the afternoons was between N and W for a significant 94% of the time, compared to the normal frequency of 77% from this direction. Two days of strong winds were recorded at Canberra Airport, on the 13th and 23rd. The highest wind gust at Canberra Airport was 70 km/hr on the 25th, although much higher gusts (113 km/hr) were recorded on the ACT ranges on the same day.

Other phenomena

Only one thunderstorm occurred in the Canberra region during the month, on the 22nd, which produced heavy showers in some northern suburbs. This was preceded by widespread raised dust which reduced visibility to 3 km over the city. Only one fog was reported at Canberra Airport compared to the normal frequency of around 4 fogs in September. The amount of sunshine averaged 8.4 hours per day, which is above the historical September average of 7.7 hours.