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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Severe to extreme heatwave conditions expected across south-east, eastern parts of Australia

00:40 EDT

The first significant heatwave of the season is here, and it's ending what's shaping up to be the nation's hottest November on record with a sizzle.

November heat records could be broken during sweltering weekend in NSW

15:56 EDT

November heat records could be broken today as the mercury climbs across New South Wales ? and there is no southerly change due until Sunday afternoon.