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
06:50 CST
24°C
31°C
Possible thunderstorm
Weather News
Cattle stations in central Arnhem Land rejoice as massive downfalls signal early start to wet season
15:52 EST
Cattle stations across the Top End of the Northern Territory are celebrating an early start to the wet season with record totals in some areas.
More rain for flooded states
14:02 EST
Australia's four flood-affected states will receive another burst of rain in the next two days.
Northern Territory weather records tumble as September deluge hits
13:43 EST
Rainfall records have tumbled in the Northern Territory after a weekend deluge brought heavy falls to parts of the Top End.
