|WA Seasonal Rainfall Outlook: probabilities for August to October 2005, issued 14th July 2005|
Neutral odds for exceeding median seasonal rain
Seasonal rainfall odds released today by the Bureau of Meteorology, show no strong shifts towards either wetter or drier conditions across WA for the late winter to mid-spring period (Aug-Oct).
The pattern of seasonal rainfall odds is mostly a result of continuing above average temperatures in the tropical Pacific Ocean.
For the August to October period, the chances of above median rainfall are mainly between 45 and 55% over Western Australia (see map). So in years with ocean patterns like the current, about five August to October periods out of ten are expected to be wetter than median over the State, with about five out of ten being drier. However, it should be noted that August to October includes some of the dry season across northern Australia and heavy rain is uncommon during this period.
Outlook confidence is related to the influence of Pacific and Indian Ocean temperatures on seasonal rainfall. During August to October, history shows this influence to be mostly weakly or very weakly consistent across WA (see background information).
The Southern Oscillation Index (SOI) rose strongly in June to a value of +3, well above the May value of −15. The approximate SOI for the 30 days ending 11th July was +4.
With the rise in the SOI, and continued neutral cloud and wind patterns across the tropical Pacific, the chances of an El Niño developing in 2005 are slim. Furthermore, the widespread rainfall over eastern Australia in June is consistent with a neutral Pacific as opposed to a developing El Niño. For routine updates and comprehensive discussion on the latest data relating to El Niño, together with details on what the phenomenon is and how it has affected Australia in the past, 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 16th AUGUST 2005