Agriculture Weather


Southern Oscillation Index

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  • 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

SOI

Nino3.4 Index

Nino3.4
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Weather News

Summarising rain in Darwin so far this month

13:14 EDT

La Nina has already made its presence felt in Darwin, with this month already being the wettest October since 2010 - coincident with the last strong La Nina event.

October brings more rain for Victoria

12:25 EDT

Victoria has not escaped the unsettled weather that has impacted the southeast recently, as rainfall, strong winds and the odd storm have all featured in the past 24 hours.