Seasonal Climate Outlook Message for January to April 2000

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SOI message 25th January 2000

The average SOI over the previous 30 days has fallen to +3.0. Based on the SOI, the probabilities of exceeding median rainfall during the total January to March period range between 50% and 80% over most of Queensland and New South Wales.

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Review of Climatic Forecasts and Information

Based on the latest values and trends of the SOI, the probabilities of receiving above-median rainfall over the total January-March period are relatively high for many regions of Queensland especially the Central Highlands, central coast, and parts of the northern inland.

Probabilities of exceeding median rainfall are 60-80% in the Central Highlands and central coast of Queensland, southern coastal regions of NSW and the far north-west of NSW. Conversely, there is only a 20-40% chance of exceeding median rainfall in south-western Victoria and south-western Tasmania. Remaining areas of eastern Australia have a rainfall probability little different from the 'normal' for this time of year.

The persistent 'cool' sea-surface temperature (SST) anomalies in the eastern equatorial Pacific Ocean, combined with 'warm' SST anomalies around Western Australia, suggest a continuing 'weak' La Nina pattern.

Forecasts from experimental general circulation models are currently providing mixed signals regarding changes in the La Nina pattern by mid-year. Two models (including the most highly regarded one) are forecasting the development of an El Nino pattern, two are predicting continuation of the La Nina while the others are indicating neutral conditions. However, sub-surface sea temperatures to the east of Australia are now significantly warmer than normal, in classic 'pre-El Nino' mode. In addition, the sub-tropical ridge is again expected to be further north than normal 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 over the next few months is recommended.

Combining the rainfall outlook with current soil water and pasture condition, the probabilities of above-median pasture growth during the total December-February period are 70-100% over Queensland except for the far central west.

The next passage of the main wave of the 30-50 day oscillation is expected later this week.

Last updated: 18 January 2000