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
10:50 CST
32°C
25°C
Mostly sunny
Weather News
Rockhampton braces as Fitzroy River heads toward 2011 flood level
10:56 EST
Expected flood levels in the central Queensland city of Rockhampton have been revised down, with the Fitzroy River only expected to reach 9 metres on Wednesday.
Eastern flooding update
10:09 EST
Floodwaters will continue to plague parts of eastern Australia this week in the wake of Tropical Cyclone Debbie.
NSW floods: Murwillumbah family brave deep water to save horse
08:22 EST
Two men who saved a horse from drowning at Murwillumbah have said they thought the animal would die in their arms through the night.
