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.

Display Your Local Weather

Weather News

Satellite images question how private dams filled during Murray-Darling pumping embargo

17:29 EDT

A number of farmers will be investigated after satellite imaging showed their dams, in drought-ravaged parts of New South Wales, were filled during a pumping embargo in parts of the Murray-Darling Basin.

Tropical cyclone names this season

14:18 EDT

Australia's 2019/20 tropical cyclone season officially starts in two weeks.

Galiwin'ku residents allocated housing shelter years after Cyclone Lam's havoc

12:36 EDT

Almost five years after the Arnhem Land community of Galiwin'ku was battered by Cyclone Lam, the NT Government is yet to spend $20.3 million of disaster relief funding for rebuilding housing.