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
Morning storms threatening Darwin
10:29 EDT
A line of showers and thunderstorms moving over the Northern Territory's Top End may reach Darwin later this morning.
Powerful low pressure system buffeting southeastern Australia
09:12 EDT
Damaging winds are lashing parts of southeastern Australia today, fanning bushfires and felling trees.
Dust storm hits Sydney, NSW Government issues air quality warning
00:23 EDT
A dust storm that has swept across drought-stricken parts of New South Wales has shrouded Sydney's landmarks and sparked an air quality warning from the State Government.
