WA Seasonal Rainfall Outlook: probabilities for October to December 2003, issued 16th September 2003

Above average seasonal falls for western WA

The Bureau's rainfall outlook for the December quarter shows that wetter conditions are favoured in the northeast and west of the country. In contrast, the last three months of the year are more likely to be drier than average in the far southeast. This outlook is largely the result of higher than average temperatures in the Indian Ocean.

For the October to December period, the chances of above median rainfall are between 60 and 75% across a large part of central and western WA (see map). So with climate patterns like the current, about 7 seasons out of 10 are expected to be wetter than average in these parts of the country, with about 3 out of 10 being drier. However, it is worth noting that it is a seasonally dry time of year in the Fortescue and West Gascoyne districts with heavy rain in the December quarter being uncommon.

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

In other parts of WA, the odds for above average seasonal falls are mainly between 55 and 60%.

Outlook confidence is related to the influence of Pacific and Indian Ocean temperatures on seasonal rainfall. During October to December, history shows this influence to be moderate to high across the southern half of WA, and generally moderate in the north. In contrast, the influence is weak or very weak in areas around the WA/NT/SA border (see background information).

The tropical Indian Ocean is currently warmer than average, whilst the Pacific is showing near normal temperatures. For more detail see the El Niño Wrap-Up. The excess warmth in the Indian Ocean has had the greater influence on the overall pattern of probabilities.

August's value of the Southern Oscillation Index (SOI) was –2, five points below the July value of +3. The approximate SOI for the 30 days ending 13th September was –1.


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.


August 2003 rainfall in historical perspective

June to August 2003 rainfall in historical perspective


Background Information