Hottest and very dry October
Geelong has just experienced its hottest October and one of the driest since temperature records began in 1903 and rainfall in 1871. The previously hottest October was in 1940 when the mean temperature was 15.9 degrees C, and this year it was 17.1 C. The latest 30-year average is 13.7 C. Other figures for 2015 are given in the Rainfall and Temperature paragraphs below.
The most likely culprit for the 2015 records was not man-made global warming but a combination of a very strong El Nino and a positive Indian Ocean Dipole (IOD), together with the ever-present Otways and Great Divide rain shadow effects.
When the first two features combine they provide warm dry air masses from the northeast and northwest which have full sway over southern Victoria to produce the optimum conditions for record-breaking heat and aridity.
Very low rainfall was experienced right across western Victoria including the Geelong Region. Despite a thunderstorm dumping around 10+ mm up to 9 am on the 31st, the totals remained generally below 30-50 % of normal October falls.
The urban average was only 17 mm compared to 53.8 mm which is the latest 30-year October average.
Numerous temperature records were broken in October:
1. Highest daily maximum average: 24.1 C compared to 30-year average 19.1 C. Previous highest 22.9 C in 1914.
2. Highest October mean temperature since 1903 when records began. 17.1 C compared to previous highest 15.9 C in 1940.
3. Warmest first week in October, with 3 days over 30 degrees C.
4. Six days over 30 C (equal with 1977).
5. 21 days over 20 C (average is 10.5 days).
6. 13 nights over 10 C (equal with 1963).
Maximum temperature was 35.5 C on the 5th, and the lowest overnight was 2.9 C on the 1st. Highest overnight minimum was 15.9 C on the 21st and the coldest day was the 22nd with 15.5 C.
There were three strong wind days with a maximum gust at Breakwater AWS of 78 kph on the 7th. There was one thunderstorm on the 31st, but no severe storms.