Southern Oscillation Index
The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.
A strongly and consistently positive SOI pattern (e.g. consistently above about +6 over a two month period) is related to a high probability of above the long-term average (median) rainfall for many areas of Australia, especially areas of eastern Australia (including northern Tasmania) - La Niña.
Conversely, a 'deep' and consistently negative SOI pattern (less than about minus 6 over a two month period, with little change over that period) is related to a high probability of below median rainfall for many areas of Australia at certain times of the year - El Niño.
However, it is important to remember that the pattern of relationship between SOI and rainfall (and temperature) can vary depending on the particular season and region. Additionally, the change in SOI over a specified period can be as important in understanding relationships between SOI and rainfall as is the absolute value in SOI.
Now Temperature
At Darwin Ap
13:40 CST
28°C
25°C
Possible thunderstorm
Weather News
Monsoon burst causes havoc on Darwin roads, minor flooding
14:24 EDT
It has been a wet 24 hours in Darwin, with a dumping more than 200 millimetres of rain over the city, causing havoc on the roads.
Sydney weather: City sizzles as mercury soars past 40C in some areas
14:08 EDT
Sydney's sweaty summer has continued with the mercury passing 40 degrees Celsius in parts of the city.
Man drowns rescuing girl from floodwaters in WA's Kimberley
14:02 EDT
A man has drowned after rescuing a young girl from floodwaters on the Ord River, in WA's far north Kimberley.
