Fairfax Media Network

Agriculture Weather

Southern Oscillation Index

  • location
  • Aus

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.

Southern Oscillation Index


Nino3.4 Index

Display Your Local Weather

Weather News

Darkness descending on Australia

16:55 EDT

The March Equinox occurs in Australia on Wednesday morning, marking the end of the astronomical summer in the southern hemisphere.

Cyclone Marcus: Recovery payments available for some residents, council considers removing mahoganies

16:01 EDT

Federal relief funding is now available for Top End residents affected by power outages for more than 72 hours caused by Tropical Cyclone Marcus.

BOM issues flood warning as NSW coastal regions brace for severe rainfall

15:58 EDT

Severe rainfall and potential flooding may hit the Central Coast, Newcastle, Lower Hunter and Manning Rivers from tomorrow morning, according to the Bureau of Meteorology (BOM).