|National Seasonal Rainfall Outlook: probabilities for July to September 2009, issued 23rd June 2009|
A drier season favoured in some areas
The national outlook for total rainfall over the September quarter (July to September), shows some areas, generally in the south, where there are moderate shifts in the odds favouring a drier than normal season. On the whole though, the chances of above normal falls are about the same as the chances of below normal.
The pattern of seasonal rainfall odds across Australia is a result of recent warm conditions in the Indian Ocean and an increasing level of warmth in the Pacific. The influences from these two oceans counteract each other in central Queensland and northern NSW: the Indian Ocean pattern promotes wetter conditions while the Pacific biases the climate towards a drier than normal season. In the south, the two patterns tend to reinforce each other.
For the July to September period, the chance of exceeding median rainfall is between 35 and 40% in several patches across southwest WA, SA, southwest Victoria and central Australia (see map). This means that for every ten years with ocean patterns like the current, about four years would be expected to be wetter than average during the September quarter, with about six being drier.
Over most of the country though, the chance of a wetter than average three months is between 40 and 50%.
New: An expanded set of seasonal rainfall outlook maps and tables, including the probabilities of seasonal rainfall exceeding given totals (e.g. 200 mm), is available on the "Water and the Land" (WATL) part of the Bureau's website.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During July to September, history shows this effect to be moderately consistent across most of Queensland and the NT, as well in large parts of NSW and SA. The effect is generally weakly consistent elsewhere across the country, reaching moderate only in patches (see background information).
Changes in the climate patterns across the Pacific and the latest outputs from computer models point to an emerging El Niño event. A media release regarding this was issued on 3rd June. The SOI is approximately −10 for the 30 days ending 20 June. For routine updates and comprehensive discussion on any developments please 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. More detailed forecast maps, including the probabilities of seasonal rainfall exceeding given totals, can be found here.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Grant Beard on (03) 9669 4527, Brad Murphy on (03) 9669 4409, David Jones on (03) 9669 4085.|
Regional commentary is available from the Climate Services Sections in the Bureau's Regional Offices:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 24th July 2009