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
08:30 CST
26°C
33°C
Mostly sunny
Weather News
SA weather: Port Wakefield under threat as river at Gawler peaks, SES says
09:03 EST
The South Australian town of Port Wakefield is the next focus for emergency services as flood peaks continue to move through the river systems after days of wild weather.
Tasmanian floods: Rain eases but warnings remain across the state
09:02 EST
Flood warnings are likely to stay in place across Tasmania for several days as rainfall continues, but the worst of the weather has passed, the weather bureau says.
NSW severe weather warning issued, damaging winds set to lash state's north
23:58 EST
Parts of New South Wales have been warned to prepare for wild weather overnight as a low-pressure system from Tasmania gets set to batter northern parts of the state.
