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 Niņa.
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 Niņo.
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.
Severe thunderstorms that ravaged the Hunter region and the Central Coast of New South Wales are over, the Bureau of Meteorology says, but Ausgrid and SES volunteers are still working to repair the damage.
More than 12,000 insurance claims have already been lodged with damages at an estimated $31 million following the .
Southern parts of the Gulf of Carpentaria have been lashed with heavy rain and gusty winds as a tropical low makes its presence felt.