|WA Seasonal Rainfall Outlook: probabilities for Autumn 2009, issued 20th February 2009|
Below average rainfall possible in southwest Australia in autumn
The Western Australia outlook for total autumn rainfall shows increased chances of being drier than normal over the Southwest Land Division during autumn.
The pattern of seasonal rainfall odds across Australia is mainly a result of warm conditions in the Indian Ocean in January, the Pacific Ocean had little contribution to this forecast.
The chance of exceeding median rainfall is about 40% over most of the Southwest Land Division, in other words, the chance of being drier than normal is about 60% in these areas. This means that for every ten years with ocean patterns like the current, about six years are expected to be drier than average in this region.
For the remainder of the state, the chance of exceeding median rainfall during autumn is about 50% to 60%, meaning that above average falls are about as equally likely as below average falls.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During autumn, history shows the effect to be moderately consistent across much of the state, whilst the effect is only weakly or very weakly consistent in some pockets in the north Kimberley, west Pilbara, Southwest and eastern Interior (see background information).
Some warming of the equatorial Pacific Ocean occurred in January, following cooling in December, so that sea surface temperatures (SST) in the central Pacific have now eased back to neutral values. While sub-surface waters are cool in the eastern Pacific, those in the west of the basin are warmer than normal and there are indications that these will impact on the surface in coming months. Furthermore, most current model outlooks suggest further warming in the Pacific. The most likely scenario is for conditions to remain neutral. The SOI remains positive at approximately +15 for the 30 days ending 17 February. 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 March 2009