Seasonal Climate Outlook Message for September to December 2000

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SOI message 27th September 2000

The average SOI over the previous 30 days has continued to increase to +10.6 The probability of exceeding the long-term median is 60% to 80% for parts of north-east Queensland and some parts of the south-east quarter but reduce to 50% for much of southern Queensland.

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Review of Climate Forecasts and Information

As mentioned in previous forecast releases, the dry conditions experienced over much of Queensland, and especially over southern Queensland, has been due to the unusually more northern position than usual of the sub-tropical ridge of high pressure this year. This pattern would not normally be expected to persist beyond spring, suggesting some easing of the dry conditions are possible within the next 1 or 2 months.

SOI patterns and 'phases'. The latest SOI 'phase' analysis suggests quite varying rainfall probabilities across eastern Australia for the next three months. For example, the probability of exceeding the long-term median rainfall for the Central Highlands and the north-eastern quarter of Qld is between 60% and 80%. Similarly, the probability of exceeding the long- term median for some inland parts of NE and SW NSW is also 60% to 70%. It should be remembered that a 70% probability of exceeding the long-term median for a location also means there is a 30% probability of not exceeding the median for that location. These probability values are simply statements of fact referring to the history of rainfall events for particular locations over the past 100 years.

Over southern Queensland the probability of exceeding the long-term median for the period between September and November is close to 50% but with some higher values (60% to 70%) over parts of the eastern Darling Downs and the Lockyer Valley. Conversely, over the far south-west of Queensland, parts of western NSW, and parts of northern Tasmania the probability of exceeding the long-term median is 30% to 40%..

Sea-surface temperatures. Sea-surface temperatures in the Pacific and Indian Oceans are generally close to average at the moment, although there are patches of cooler than normal temperature in the far eastern equatorial Pacific. Some general circulation models are suggesting or hinting at the potential for warming in the eastern Pacific over the next 6-9 months. We will keep a close watch on these developments to determine any potential for El Nino development or otherwise next year. We suggest close monitoring of sea-surface temperature patterns over the next 6 months.

Pasture Growth forecasts. The probabilities of obtaining median pasture growth or better during the September to November period are average to above- average over most of Qld. They are 60-90% from Cape York Peninsula to parts of the Warrego (that is, 10-40% probability of obtaining below-median growth). However, probabilities are only 10-40% in south-eastern Qld (and also in the south-western corners) due to the current low soil-moisture levels (that is, 60-90% probability of obtaining below- median growth).

30-50 Day Oscillation. The next passage of the 30- to 50-Day Oscillation over Qld is expected about the second week in October.

More detailed information for your location can be obtained from the Australian Rainman software package. Also additional information is available the internet site 'The Long Paddock', our Farmlink system, or by phoning Col Paull (07 3896 9587) or Drs Allyson Williams or Roger Stone (climatologists) on 07 4688 1407/ 0746881293 or Roger's Mobile 0412559408.