THE 30-DAY average of the Southern Oscillation Index (SOI) has risen to + 1.5 as of 1 October. There has been a corresponding lift in rainfall probabilities across much of Queensland and northern NSW for October- December (refer to map).
Gaining a 60- 70 per cent probability of getting or exceeding their median rainfall are parts of the Chinchilla, Wondai, Mundubbera, Gayndah, Perry, Monto, Murweh, Blackall, Jericho, Aramac, Longreach, Winton, Mt Isa, Bourke, Cloncurry, Nebo and Duaringa shires. (Refer to map for other probabilities.)
For much of NSW, this increase in the value of the SOI will subdue rainfall probabilities for October- December. The probability of getting or exceeding the median rainfall in most areas of NSW is 20-50 per cent.
The exception to these low-rainfall probabilities in NSW is in the north, along the Queensland border, some coastal regions and parts of the New England tablelands, where there is a 50-70 per cent probability of above-median rainfall over this three-month period.
For those who like to follow historical patterns more closely, years in the past November 2001 that had a Rapidly Rising SOI phase for August-September include 1989, 1983, 1979, 1970, 1949, 1936, 193 I, 1926, 1922 and 1921.
Recent research has shown that a Rapidly Rising SOI phase at the end of September increases the potential for severe storm activity in the coming months over southern Queensland and northern NSW.
Also of interest is the trend of Sea Surface Temperature (SST) changes in the central Pacific Ocean. This partially resembles sea surface temperature patterns and trends experienced throughout 1992-94. lt will be interesting to see if this warming trend in the central Pacific Ocean continues and, if so, by how much.
Further substantial warming of SST in this region could be considered an early warning of the potential reduction in expected rainfall across northern Australia and PNG over late summer and well into next year. Even though the outlook for the medium term has improved slightly, many climate research institutions around the world believe the necessary preconditions required for the onset of an EI Nino in the longer term still exist.
The key point at present is to keep track of any shifts in the SOl value and changes in sea surface temperature patterns, as these will provide the indicators to rainfall probabilities for summer and into next year.
More climate-related information is available on the DPI's climate web site www.dpi.qld.gov.au/climate or by contacting the DPI Call Centre on 13 25 23. A recorded message with the 30-day average of the SOI is available on 074688 1439.