WA Seasonal Rainfall Outlook: probabilities for Autumn 2004, issued 17th February 2004

Mixed autumn rainfall odds in WA

The Bureau's autumn rainfall outlook for Western Australia shows that a drier than average season is more likely in the southwest, whereas above average falls are more likely further north in parts of the Pilbara and Gascoyne. The outlook probabilities have arisen from the combined effects of above average temperatures in both the Pacific and Indian Oceans.

For the March to May period, the chances of above median rainfall are mainly between 35 and 40% in southwest WA (see map), meaning BELOW median falls have a 60 to 65% chance of occurring. So with climate patterns like the current, about 6 seasons out of 10 are expected to be drier than average in this area, with about 4 out of 10 being wetter. Conversely, the chances of above median falls are slightly above 60% over some of the areas to the south and southeast of Karratha.

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

Across most of the State though, the chances of a wetter than average autumn vary between 50 and 60%.

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

Both the Indian and tropical Pacific Oceans remain warmer than average, the former having a warming trend during January. 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. January's value was –12 which followed the +10 recorded in December. The approximate SOI for the 30 days ending 14th February was +3.


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

January 2004 rainfall in historical perspective

November 2003 to January 2004 rainfall in historical perspective


Background Information