FYI: Monthly Climate Summary for Canberra - August 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

A warm August 2009 for the ACT

• 9th warmest August on record
• Above average minimum temperatures
• Warmest August night on record at Canberra Airport on the 24th (12 °C)
• Below average rainfall

Rainfall

Canberra Airport recorded a total rainfall of 37.4 mm during the month, which is slightly below the historic average of 46.0 mm. However, the number of rain days was above average at 14 days (August average 11 days), which is the highest since 1990 (when 19 rain days).

Prevailing high pressure systems over NSW and lack of any significant rain producing systems contributed towards the below average rainfall in the ACT. The majority of rain occurred during three main events, a low pressure system on the 12th and cold fronts on the 22nd and 30th.

Monthly totals for August ranged from a high of 142.8 mm at Corin Dam in the highlands SW of Canberra to a low of 21.8 mm at Watson (Racecourse).

Temperatures

The mean maximum (daytime) temperature at Canberra Airport was 14.5°C, which is 1.5°C above the historical average of 13.0°C. This is the 9th warmest August in the 71 year record for Canberra. The highest mean maximum temperature in the ACT was 14.7°C at Tuggeranong, with this location also recording the warmest day of the month of 19.1 °C on the 23rd. Prevailing NW winds and the lack of any significant cool changes, contributed towards the mild daytime temperatures.

Nights were generally mild, with the mean minimum temperatures at Canberra Airport of 2.4°C, 1.4°C above the August average of 1.0 °C. On the 24th, Canberra Airport recorded its highest minimum temperature on record for August with 12.0 °C which is 11 °C above the historic August minimum. There were only 11 frosts during the month (minimum temperature below zero deg) compared to the normal 19 frosts for August. The lowest temperature in the ACT was -6.3 °C at Mt Ginini on the 8th and 26th while the lowest in Canberra suburbs was -5.5 °C at Tuggeranong AWS on the 9th.

The mild temperatures were mainly due to prevailing N-W winds throughout the month, bringing warm dry air to much of NSW and the ACT.

Some sites had their warmest August night (highest daily minimum temperature) on record.

Wind

The prevailing wind direction over Canberra during the afternoons was W-NW for around 87% of the time, well above the average frequency of about 63% for this direction in August. The prevailing wind direction during the mornings was N-NW at about 45% of the time, compared to the usual 32% from this direction. Three days of strong wind were recorded at Canberra Airport on the 7th, 25th and 30th of August. The highest wind gusts were recorded on the 25th, with 109 km/h at Mt Ginini AWS and 89 km/h at Canberra Airport.

Other phenomena

Two thunderstorms occurred in the Canberra region, on the 11th and 29th of August, the former associated with small hail. The frequency of fog was slightly below average, with only 3 fogs reported at Canberra Airport compared to the normal frequency of around 5 days of fogs. The amount of sunshine averaged 7.2 hours per day, which is slightly above the historic average for August of 7.0 hours.