National Seasonal Rainfall Outlook: probabilities for October to December 2004, issued 16th September 2004

Increased risk of dry conditions in far southeastern Australia

There is a moderate shift in the odds towards below average rainfall for the December quarter (Oct-Dec) in the far southeast of the mainland and parts of northern Tasmania, the Bureau of Meteorology announced today. For the rest of the country, the chances of accumulating at least average rain over the last three months of 2004 are mostly close to 50%.

However, when looking at the growing season (April-November) as a whole over southern and eastern Australia, widespread below to very much below average falls up to the end of August mean that many places are unlikely to reach their total growing seasonal average by the end of November. The chances of receiving the required rain are widely below 20%, dropping to below 10% along the east coast. For more information on the recent dry conditions, see the Drought Statement.

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

In the far southeast of SA and the adjacent parts of southwest and south-central Victoria, together with some of northern Tasmania, the chances of above median rainfall for the December quarter are between 35 and 40%. So in years with ocean patterns like the current, about six October to December periods out of ten are expected to be drier than average in these areas, with about four out of ten being wetter.

In contrast, parts of northwest 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.

The current pattern of outlook probabilities is due to recent temperature patterns in both the Pacific and Indian Oceans.

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 chance of a late-developing El Niño event increased over the past month, with several but not all indicators reaching their El Ni˜o thresholds. The mounting evidence includes warming of the central Pacific, reduced Trade Winds in the same area and continued negative values of the Southern Oscillation Index (SOI) which came in at –8 for August. The approximate SOI for the 30 days ending 13th September was –3.

For routine updates 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 El Niño 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: Felicity Gamble on (03) 9669 4256, Blair Trewin on (03) 9669 4085
Regional versions of this media release are available: | Qld | NSW | Vic | Tas | SA | WA | NT |

Regional commentary is available from the Climate and Consultancy Sections in the Bureau's Regional Offices:
Queensland -(07) 3239 8669 or (07) 3239 8666
New South Wales -(02) 9296 1522
Victoria -(03) 9669 4949
Tasmania -(03) 6221 2043
South Australia -(08) 8366 2664
Western Australia -(08) 9263 2222
The Northern Territory -(08) 8920 3813



Corresponding temperature outlook

August 2004 rainfall in historical perspective

June to August 2004 rainfall in historical perspective


Background Information