|WA Seasonal Rainfall Outlook: probabilities for July to September 2007, issued 26th June 2007|
50:50 chances for above average September-quarter rainfall
The Western Australian outlook for total September-quarter rainfall (July to September), shows no strong swings in the odds towards either above-normal or below-normal rainfall. Over WA the chances of accumulating at least average rain for the season are relatively close to 50%.
The pattern of seasonal rainfall odds across WA is mainly a result of recent higher than average temperatures in parts of the tropical and sub-tropical Indian Ocean.
The chances of exceeding the median rainfall for the July to September period are mostly between 45 and 55% across Western Australia (see map). So in years with ocean patterns like the current, about five September-quarters out of ten are expected to be wetter than average across the State and five out of ten are expected to be drier.
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).
The Southern Oscillation Index (SOI) remained neutral in May and April with a value of −3 in both months. However, the SOI has risen over the past month to an approximate 30-day value as at 23rd June of +12. Computer models are still predicting the development of La Niña during winter. For routine updates and comprehensive discussion on any developments 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 24th JULY 2007