Seasonal Climate Outlook Message for June to September 2000

The bottom line

The average SOI over the previous 30 days has continued to drop to -4.9 . Based on the SOI, the probabilities of exceeding median rainfall during the total June to August period are little different from the 'normal' for this time of year in most of the eastern States of Australia, except for the south-eastern corner of Qld and the north-eastern corner of NSW where the probabilities are 30-40%; and parts of eastern NSW, western Victoria and eastern Tasmania where probabilities are 60-70%.

The full story

Based on the latest values and trends of the SOI, the probabilities of receiving above-median rainfall over the total June to August period are little different from the 'normal' for this time of year in most of the eastern States of Australia. Exceptions are the south-eastern corner of Qld and the north-eastern corner of NSW where the probabilities are 30-40%; and parts of eastern NSW, western Victoria and eastern Tasmania where probabilities are 60-70%.

The 'cool' sea-surface temperature (SST) anomalies that have been present since 1998 in the central and eastern equatorial Pacific Ocean have receded. However, there are still patches of cool anomalies, particularly from the International Dateline to the central Pacific. The strength of the atmospheric circulation, typical of a La Niña pattern, has also weakened, but not to the same extent.

In general, this recession of the La Niña was forecasted by experimental general circulation models. Most of these forecasts are suggesting that neutral conditions will dominate at least until summer. Also some research suggests the sub-tropical ridge may again be further north than normal this winter, which tends to reduce winter rainfall from the Goondiwindi district through to the Central Highlands. As these indicators provide some cause for concern, regular monitoring of them and the SOI is highly recommended.

Frost risk this winter is detailed in a new DPI book 'Frost Risk in Eastern Australia and the Influence of the Southern Oscillation' by Jacqui Willcocks and Roger Stone. There is an increased chance of an earlier finish to the frost season by 1-2 weeks for some towns in Queensland. Although the frost season can be shorter, the expected number of frosts is about the same as average, and the chance of getting at least one frost is similar to the average.