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
12:40 CST
34°C
25°C
Mostly sunny
Weather News
Rain, storms and snow loom for Australia's southeast
11:36 EST
The best rain in three-to-six months will soak parts of the Murray-Darling Basin during the next three days, before a wintry blast grips Australia's southeast.
Far north QLD gets a drenching
09:31 EST
Heavy rain has fallen over Queensland's far north and there is more tropical activity on the cards this week.
NSW School-children say YES to sunshine
12:51 EST
New South Wales: The Premier State, the state other states love to hate.
