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.
Dark and ominous clouds developed over southern parts of the ACT yesterday afternoon amid a deep and unstable low pressure trough.
For those seeking the perfect weather for the perfect date this Valentine's weekend, Australian capital cities seem sure to share the love! Brisbane and Darwin will be hot and steamy as per usual, expecting a maximum temperature into the low 30s on both days.
Queensland's first cyclone of the season poses no immediate threat to the coast but may whip up dangerous swells for south-east beaches early next week, the Bureau of Meteorology (BoM) says.