Seasonal Climate Outlook Message for September to December 2000

The bottom line

SOI message 20th September 2000 The average SOI over the previous 30 days has continued to increase to +9.2 . Based on the SOI, the probabilities of receiving or exceeding median rainfall during the total September to November period are 60-70% in parts of north-east Qld, and mostly between 40-60% for the rest of the state.

The full story

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 influence will persist during Spring, but decrease as it moves south in summer.

Years in the past when the SOI was similar to the present include 1971, 1963, 1962, 1957, 1929 and 1925. Years when the high-pressure cells were northerly than usual include 1968-69 and 1979-80.

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 slightly cooler than normal. However, SSTs off the southern half of Western Australia, and other southern States, 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.

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).

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