|WA Seasonal Rainfall Outlook: probabilities for July to September 2009, issued 23rd June 2009|
A drier season favoured in southwest WA
The Western Australian outlook for total rainfall over the September quarter (July to September), shows a moderate bias in the odds favouring a drier than normal season in parts of southwest WA. There are about equal chances of either wetter or drier conditions for the remainder of the state.
The pattern of seasonal rainfall odds across WA is a result of recent warm conditions in the Indian Ocean and an increasing level of warmth in the Pacific.
For the July to September period, the chance of exceeding median rainfall is between 35 and 40% in parts of southwest WA (see map). This means that for every ten years with ocean patterns like the current, about four years would be expected to be wetter than average during the September quarter in these areas, with about six being drier.
For the remainder of the state, the chance of a wetter than average three months is mostly between 40 and 50%.
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 July to September, history shows this effect is generally weakly consistent across a large part of WA, reaching moderate only in patches (see background information). Therefore, caution should be used when applying this outlook in southwest WA.
Changes in the climate patterns across the Pacific and the latest outputs from computer models, point to an emerging El Niño event. A media release regarding this was issued on 3rd June. The SOI is approximately −10 for the 30 days ending 20 June. 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 24th July 2009