WA Seasonal Rainfall Outlook: probabilities for August to October 2004, issued 13th July 2004

Seasonal rainfall odds close to 50:50 in WA

There are no strong shifts in the odds towards either above or below average three-month falls for the August to October period, the Bureau of Meteorology announced today.

The current pattern of outlook probabilities is due to mainly near average temperatures in the Pacific and Indian Oceans.

For Western Australia, the odds of above median rainfall are close to 50:50, meaning that they're too weak to offer any firm guidance as to the most likely outcome for late winter to mid-spring rainfall. So in years with ocean patterns like the current, about five August to October periods out of ten are expected to be wetter than average, with about five out of ten being drier.

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

However, it should be noted that in the Pilbara and Kimberley, August to October is typically a dry time of year and heavy rain is uncommon during this period.

Outlook confidence is related to the influence of Pacific and Indian Ocean temperatures on seasonal rainfall. During August to October, history shows this influence to be mostly weakly or very weakly consistent across WA (see background information).

Both the Indian and tropical Pacific Oceans remain a little warmer than average. For more detail see the the El Niño Wrap-Up.

The Southern Oscillation Index (SOI) has continued its strongly fluctuating behaviour with a June value of –14, following the May reading of +13 and April's –15. The approximate SOI for the 30 days ending 10th July was –16.


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

June 2004 rainfall in historical perspective

April to June 2004 rainfall in historical perspective


Background Information