WA Seasonal Rainfall Outlook: probabilities for Summer 2004/2005, issued 19th November 2004

Neutral outlook for WA summer rainfall

The chances of accumulating at least average summer (Dec-Feb) rain are close to 50% in Western Australia, the Bureau of Meteorology announced today. So there are no large swings in the odds towards either above or below average rainfall.

probability of exceeding median rainfall - click on the map for a larger version of the map

So in years with ocean patterns like the current, about five summers out of ten are expected to be drier than average in WA, with about five out of ten being wetter. The current pattern of outlook probabilities is mainly due to above average temperatures in both the Indian and Pacific Oceans.

Outlook confidence is related to the influence of Pacific and Indian Ocean temperatures on seasonal rainfall. During summer, history shows this influence to be moderately consistent across much of WA (see background information).

Progress towards a late-developing El Niño event has slowed over the past two months, with consistent cloud and wind patterns failing to materialize. The central Pacific remains warmer than average and at levels consistent with El Niño, but the Southern Oscillation Index (SOI) was only weakly negative, coming in at –4 for October. The approximate SOI for the 30 days ending 16th November was –5.

For routine updates 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 El Niño 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.


Corresponding temperature outlook

October 2004 rainfall in historical perspective

August to October 2004 rainfall in historical perspective


Background Information