Fairfax Media Network

Agriculture Weather


Southern Oscillation Index

  • location
  • 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
Display Your Local Weather

Weather News

Broome smashes annual rainfall record in less than two months as Cyclone Kelvin caps big wet

11:03 EDT

Broome has officially endured its wettest year on record after more than two years' worth of rain fell on the Kimberley in the past two months.

Cyclonic Queensland surf hits its peak today, Gold Coast beaches still closed

18:58 EDT

Cyclonic swells have peaked along southern Queensland beaches today, with conditions this morning described as "good as you can get" for experienced surfers.

Tropical Cyclone Kelvin weakens, but heavy flooding cuts off Great Northern Highway

18:39 EDT

A cyclone which brought damaging winds and heavy rain to northern WA has weakened to a tropical low, but there are fears flooding affecting a major supply road could impact food delivery in the region.