|WA Seasonal Rainfall Outlook: probabilities for May to July 2009, issued 24th April 2009|
Higher seasonal rainfall favoured in parts of northern WA
The WA outlook for total rainfall over the late autumn to mid-winter period (May to July), shows a moderate shift in the odds favouring a wetter than normal season in parts of northern WA.
The pattern of seasonal rainfall odds across Western Australia is mainly a result of warm conditions in the Indian Ocean in February; the Pacific Ocean had little contribution to this forecast.
For the May to July period, the chance of above median rainfall is between 60 and 65% in the east Kimberley, despite the east Kimberley region being seasonally dry at this time of year. This means that for every ten years with ocean patterns like the current, about six or seven years are expected to be wetter than average over these parts of the east Kimberley, while about three or four years are expected to be drier.
Across the rest of WA, the chance of exceeding the median rainfall during the coming three months is between 45 and 60%, meaning that above average falls are about as equally likely as below average falls throughout most of the state.
New: Under the WATL part of the Bureau's website, there is an expanded set of seasonal rainfall outlook maps and tables, including the probabilities of seasonal rainfall exceeding given totals (e.g. 200 mm).
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the May-July period, history shows this effect to be moderately consistent in patches through various regions of Western Australia. However, in some parts the effect is only weakly or very weakly consistent, most notably in the climatologically wetter regions of southwest WA (see background information).
Pacific climate patterns are currently neutral and the consensus from computer models is for near average tropical Pacific surface temperatures in the middle of the year, although with some warming from present values. The SOI is approximately +8 for the 30 days ending 21 April. 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 26th May 2009