|National Seasonal Rainfall Outlook: probabilities for October to December 2005, issued 15th September 2005|
Mixed rainfall outlook for December quarter
Northwest to central WA faces the prospect of increased rainfall during the December quarter (October to December), but the odds have swung towards drier than average conditions in parts of the east, the Bureau of Meteorology announced today. However, the chances of accumulating at least median three-month rainfall are close to 50% across most of the country.
For the October to December period, the chances of above median rainfall are between 30 and 40% in a band extending from the far southeast of South Australia to West Gippsland and over most of Tasmania (see map). This includes most of the areas that have been suffering severe short-term rainfall deficiencies since the start of autumn, and a general downturn in rainfall since the mid 1990s. See the Drought Statement for more information. The chances of a wetter than average season also drop below 40% over an area of north Queensland inland from Townsville.
So in years with ocean patterns like the current, about three or four December quarters out of ten are expected to be wetter than the median over these parts of eastern Australia, with about six or seven out of ten being drier.
In contrast, parts of northwest to central WA have an increased likelihood of a wetter than average October to December period, with probabilities in the 60 to 65% range. It should be noted though, that the December quarter is a seasonally dry time of year in parts of WA's Gascoyne and Pilbara districts with heavy rain being uncommon.
Outlook confidence is related to the influence of Pacific and Indian Ocean temperatures on seasonal rainfall. During the December quarter, history shows this influence to be moderately consistent across much of the country (see background information).
The Southern Oscillation Index (SOI) fell from +1 in July to −7 in August. However, the SOI has begun to rise again with the approximate value for the 30 days ending 12th September being −1.
With all the main tropical Pacific climate indicators remaining neutral, an El Niño event developing in 2005 is not considered a realistic possibility. For routine updates and comprehensive discussion 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 ENSO 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.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Grant Beard on (03) 9669 4527, Blair Trewin on (03) 9669 4603, Andrew Watkins on (03) 9669 4360.|
Regional commentary is available from the Climate and Consultancy Sections in the Bureau's Regional Offices:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 18th OCTOBER 2005