WA Seasonal Rainfall Outlook: probabilities for May to July 2004, issued 19th April 2004

Neutral seasonal rainfall odds

The Bureau's seasonal rainfall outlook for the coming three months shows the chances of exceeding the median are close to 50:50 in Western Australia. This outlook pattern is a result of the combined effects of above average temperatures in both the Pacific and Indian Oceans.

For the May to July period, the chances of above median rainfall are mainly between 45 and 55% across WA (see map). So with climate patterns like the current, about five May to July periods out of ten are expected to be wetter than average over the State, with about five out of ten being drier.

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

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

Both the Indian and tropical Pacific Oceans remain warmer than average, although there has been a cooling trend in each. For more detail see the the El Niño Wrap-Up.

The Southern Oscillation Index (SOI) has shown strong month-to-month variations recently, in association with active and inactive phases of the northern Australian monsoon. March's value was zero following February's +9 and –12 in January. The approximate SOI for the 30 days ending 15th April was –20.


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

March 2004 rainfall in historical perspective

January to March 2004 rainfall in historical perspective


Background Information