|WA Seasonal Rainfall Outlook: probabilities for Spring 2009, issued 26th August 2009|
Wetter than normal conditions favoured in southwest Western Australia
The WA outlook for total rainfall over spring (September to November) shows a moderate tendency in the odds favouring a wetter than normal season across much of the southwest of the state.
The pattern of seasonal rainfall odds across WA is a mainly a result of warm conditions in the Indian Ocean.
For the September to November period, the chance of exceeding median rainfall is is between 60 and 65% for most of the southwest of WA, grading to between 45 and 55% over the remainder (see map). This means that for every ten years with ocean patterns like the current, about six or seven years would be expected to be wetter than average in large parts of southwest WA.
Outside of the southwest, the chances of a wetter than normal spring are about the same as for a drier than normal one.
New: An expanded set of seasonal rainfall outlook maps and tables, including the probabilities of seasonal rainfall exceeding given totals (e.g. 200 mm), is available on the "Water and the Land" (WATL) part of the Bureau's website.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During spring, history shows this effect to be moderately consistent for the southwest of WA and northern Kimberley, but only very weakly consistent for the remainder (see background information).
An El Niño event looks to be developing across the Pacific: the latest outputs from computer models indicate it will reach peak intensity late in the year. El Niño events are usually (but not always) associated with below normal rainfall in the second half of the year across large parts of southern and inland eastern Australia. The SOI is approximately −7 for the 30 days ending 23 August. 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 detailed forecast maps, including the probabilities of seasonal rainfall exceeding given totals, can be found here.
|More information on this outlook is available from 8.30am to 4.30pm (WST) Monday to Friday by contacting the Climate Services Centre in the Bureau's Perth Office: (08) 9263 2222.|
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 22nd September 2009