|National Seasonal Rainfall Outlook: probabilities for August to October 2005, issued 14th July 2005|
Decreased seasonal falls more likely in northeastern Australia
Seasonal rainfall odds released today by the Bureau of Meteorology, indicate an increased likelihood of below median falls over northeastern Australia and a few small patches in the southeast. The chances of accumulating at least median rain during the late winter to mid-spring period (Aug-Oct) are close to 50% across remaining parts of the country.
The pattern of seasonal rainfall odds is mostly a result of continuing above average temperatures in the tropical Pacific Ocean.
For the August to October period, the chances of above median rainfall are between 30 and 40% over most of northern and western Queensland and the adjacent border areas of far northeast SA and far northwest NSW (see map). In north central Queensland the probabilities drop a little below 30%. So in years with ocean patterns like the current, about three August to October periods out of ten are expected to be wetter than median over northeast Australia, with about seven out of ten being drier. However, it should be noted that August to October includes some of the dry season across northern Australia and heavy rain is uncommon during this period.
In parts of southwest Victoria and northern Tasmania the chances of above median seasonal falls are a little below 40%, indicating about a six out of ten chance of below median rain. However, as far as Victoria is concerned this outlook should be used with caution because ocean temperatures only have a weakly consistent influence on seasonal rainfall at this time of year.
Outlook confidence is related to the influence of Pacific and Indian Ocean temperatures on seasonal rainfall. During August to October, history shows this influence to be moderately consistent across most of Queensland, the east and north of the NT and the northern inland of NSW. Elsewhere, it is generally weakly consistent, reaching moderate only in patches, including northern Tasmania (see background information).
The Southern Oscillation Index (SOI) rose strongly in June to a value of +3, well above the May value of −15. The approximate SOI for the 30 days ending 11th July was +4.
With the rise in the SOI, and continued neutral cloud and wind patterns across the tropical Pacific, the chances of an El Niño developing in 2005 are slim. Furthermore, the widespread rainfall over eastern Australia in June is consistent with a neutral Pacific as opposed to a developing El Niño. 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, Andrew Watkins on (03) 9669 4360, David Jones on (03) 9669 4085|
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 16th AUGUST 2005