|WA Seasonal Rainfall Outlook: probabilities for July to September 2006, issued 27th June 2006|
Risk of further below average rainfall in southwest WA
There is a moderate shift in the odds towards below average September quarter (July-September) rainfall across a significant part of southwest Western Australia, the Bureau of Meteorology announced today. The autumn-early winter rainy season has been very dry in southwest WA, so a persistence of below average falls would have serious consequences.
The pattern of seasonal rainfall odds across Australia is largely a result of above average temperatures in the Pacific Ocean. Conditions in the Indian Ocean are near normal and have had little influence on this outlook.
For the July to September period, the chances of above median rainfall are between 35 and 40% over parts of southwest WA (see map). This means that below average falls have a 60 to 65% chance of occurring in these regions. So in years with ocean patterns like the current, about six September quarters out of 10 are expected to be drier than average in these areas of southwest WA, with about four out of ten being wetter.
In contrast, a small part of the Gascoyne in WA has an increased risk of above average seasonal falls. The chance that the seasonal total will exceed the median in this area is 60 to 65%. For much of WA though, the chances are close to 50% for accumulating at least the long-term median rain during the coming three months.
However, it should be noted that July to September is the heart of the dry season across northern Australia and heavy rain is uncommon during this period.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During July to September, history shows this effect to be moderately consistent in parts of central and eastern WA, but only weakly consistent across most of the State, including the southwest (see background information).
After moderately positive values of +14 and +15 in March and April respectively, the Southern Oscillation Index (SOI) dropped substantially in May to a value of −10. The approximate SOI for the 30 days ending 24th June is −9.
It is likely that neutral ENSO conditions will remain in place for the remainder of 2006. For routine updates and comprehensive discussion on the latest data relating to ENSO, together with details on what the phenomenon is and how it has affected Australia in the past, please see the ENSO Wrap-Up.
Click on the map above for a larger version of the map. Use the reload/refresh button to ensure the latest forecast map is displayed.
|More information on this outlook is available from 9.00am to 5.00pm (WST) Monday to Friday by contacting the Climate and Consultancy section in the Bureau's Perth Office: (08) 9263 2222.|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 25th JULY 2006