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.
If you wanted to stay a bit warmer today, a dip in the ocean is probably your best bet, despite the rain.
Once the southerly change bumped into a low pressure trough sitting just off the Sydney coast last night, things became electric between the two.
Flood-affected farmers in the Ravensthorpe shire on the south coast of WA say the State Government has been slow in reacting to their plight, adding there is a lack of comprehension around the scale of the damage.