SOI message 20th September 2001
The 30day value of the SOI as of the 19th of September is -6.1.
The movement of the 30day average of the SOI through to the end of this month will provide the indicator as to what the late spring/early summer outlook will be.
Based on the SOI through July/August, the chance of receiving median rainfall in the next three months is somewhat varied across Queensland. Parts of north and central Queensland (Croydon, Mareeba, Etheridge, Dalrymple, Bowen, Belyando, Nebo, Peak Downs and Emerald shires) only have a low 30-40% probability of getting or exceeding the long term median September - November rainfall.
For the south east quarter of Queensland there is a 50-60% chance of getting above the long term median September - November rainfall. For the rest of the state there is a 40-50% probability of getting above the long term median September - November rainfall.
Also of interest at present 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 the 1992-94 period. It will be interesting to see if this warming trend in the central Pacific Ocean continues and if so by how much. Further substantial warming in this region could be considered an early warning of the potential reduction in expected rainfall across northern Australia and PNG over the coming summer.
Therefore the key point at present is to keep track of any shifts in the SOI value and SST pattern as these will provide the indicators as to rainfall probabilities for the coming summer.
Review of Climate Forecasts and Information 1st September 2001. Next update 1st October 2001.
Climate pattern and SOI 'phase'. Based on the latest values and trends of the SOI, the probabilities of receiving at least the long-term median rainfall over the September-October-November period are mostly around 50% for most of eastern Australia, although there are exceptions.
However, in Queensland, parts of the Croydon, Mareeba, Etheridge, Dalrymple, Bowen, Belyando, Nebo, Peak Downs and Emerald shires have only a 30-40% chance of getting above the long term September-November totals.
Although the regions of southern Queensland that are drought affected have a 50% chance of getting at least median rain over the next 3 months, it needs to be noted that September is normally one of the driest months of the year. There are low probabilities of "drought breaking" rainfall events. For example for the September/November period there is only a 20% chance of getting 210mm at Chinchilla.
Note that a 70% probability of receiving the long-term median for a location also means there is a 30% probability of not receiving 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.
Sea-surface temperatures (SSTs). Sea surface temperatures in the key regions of the eastern equatorial Pacific Ocean are mainly close to average or slightly warmer than average. Most of the SST prediction models are predicting that ocean temperatures in key regions of the Pacific Ocean will continue to slowly warm which is of concern. However, there is still uncertainty about the severity of the warming. An El Niño is when the eastern Pacific is between 1 and 2oC warmer than average.
Pasture Growth forecasts. Most of Queensland has less than a 40% chance of exceeding median pasture growth during the August-October period. However southern Queensland around the Maranoa district does have probabilities as high as 90%.
30 to 50-Day Oscillation. The 30-50 day oscillation has been difficult to track in recent times. Although the signals are weak, we expect it to next influence Queensland rainfall around the end September/start of October. More detailed information for your location can be obtained from the Australian Rainman software package. Also additional information is available on our internet site 'The Long Paddock', or by phone Dave McRae 4688 1459, Dr Allyson Williams or Dr Roger Stone (climatologists) on 07 4688 1407, 07 4688 1293 or Roger's Mobile 041 255 9408. Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Queensland Centre for Climate Applications, has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter. Contributions by Bureau of Meteorology are gratefully acknowledged.