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.

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Weather News

Rain and storms returning to eastern, southeastern Australia

16:18 EST

After a run of relatively dry and at times showery weather in recent weeks, a more substantial outbreak of rain and thunderstorms will sweep across Australia eastern and southeastern states next week.

Be very grateful the AFL Grand Final is not being played in Melbourne this Saturday

14:13 EST

We should all be grateful that the 2021 AFL Grand Final between the Melbourne Demons and Western Bulldogs is being played at Optus Stadium in Perth rather than at the MCG, because Melbourne's Saturday weather does not look good.

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