Seasonal Climate Outlook Message for September to December 2000

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SOI message: 6th September 2000.

The average SOI over the previous 30 days has continued to increase to +6.1. Based on the SOI, the probabilities of getting or exceeding median rainfall during the total September to November period are little different from the 'normal' for this time of year in most of the eastern States of Australia.

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Review of Climatic Forecasts and Information

Based on the latest values and trends of the SOI, the probabilities of receiving median rainfall or better over the total September to November period are little different from the 'normal' for this time of year in most of the eastern States of Australia. This means there are equal chances of receiving above-median or below-median rainfall.

Exceptions are parts of the Central Highlands and north-eastern quarter of Qld, and some inland parts of north-eastern and south-eastern NSW where probabilities are 60-70%; and parts of northern Tasmania where they are 30-40%.

However, the current dry conditions over much of Qld have been partially due to the high-pressure cells travelling further north than normal. This will most likely continue to have an effect through spring and may reduce the effect of a rising SOI phase on the chances of above-median rainfall.

Years in the past when climatic indicators were similar to the present include 1971, 1963, 1962, 1957, 1929 and 1925.

Sea-surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean are now close to the long-term average. Ocean temperatures off the Qld and northern Australian coastline are now slightly cooler than normal. However, SSTs off the southern half of Western Australia are significantly warmer than normal.

With regard to the future development of climatic patterns, most forecasts from the best experimental general circulation models are suggesting that neutral conditions will continue though summer, and that SST's in the eastern equatorial Pacific will become slightly warmer than average.

There is a high probability that the frost season will finish one to two weeks earlier than normal in some districts of Queensland. However, the expected number of frosts, and the chances of getting at least one frost, are about average.

Current soil moisture levels are low over much of Qld. When this is combined with the seasonal rainfall outlook, the probabilities of obtaining median pasture growth or better during the August-October period are only 10-40% over much of the State. However, pasture growth during this period is generally low, but can be valuable in terms of animal nutrition.

The next passage of the 30- to 50-Day Oscillation over Qld is expected towards the end of the first week in September.