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.
Farmers near Forbes in the New South Wales central west are bracing for extensive loses as their crops continue to be inundated with flood waters, which are expected to peak later today.
At least 100 properties have been impacted by flood waters and people have been evacuated from Forbes in central-western NSW, as floodwaters cut off roads and cause widespread damage to crops.
Southwestern parts of Western Australia have had rain of up to 24mm of rain this morning as another cold front swept over the region.