Fairfax Media Network

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.

Display Your Local Weather

Weather News

Myer redevelopment flooding: Water still entering site from Hobart Rivulet

14:21 EST

Construction workers are still trying to stop water leaking into the Myer department store in Hobart's CBD, which remains closed due to flooding.

Winton dinosaur museum open for business after two-week closure due to floodwaters

12:40 EST

Visitors can again make it through to the Australian Age of Dinosaurs Museum in outback Queensland after floodwaters forced the iconic attraction to shut up shop for two weeks.

Snow season well and truly back on track

12:38 EST

So far this snow season could be described as a yo-yo, it's up and down yet always fun.