Seasonal Climate Outlook August - October 2009
The Bureau of Meteorology released its rainfall outlook for August to October on 24 July. The outlook reports a moderate shift in the odds favouring drier than normal conditions for western Victoria. The chances of exceeding the median rainfall in western Victoria are between 30% and 40%. The chances of a wetter than average season in southeast Victoria remain between 40% and 50%.
The Bureau issued its latest ENSO Wrap-Up on 22 July 2009. The Bureau continues to report the overall likelihood of a developing El Niño event during 2009, due to above average Pacific Ocean temperatures, and cloud and rainfall patterns along the equator consistent with such an event. However, the Southern Oscillation Index (SOI) was reported as strongly positive over the past 30 days, which is contrary to typically negative SOI values characteristic of El Niño events. Nevertheless, this is expected to fall to negative values again in coming weeks, and computer modelling continues to suggest a high probability of an El Niño event in 2009.
El Niño events are usually (but not always) associated with below normal rainfall in the second half of the year across large parts of southern and inland eastern Australia. The value of the Indian Ocean Dipole (IOD), as measured by the Dipole Mode Index (DMI), has fallen steadily since the middle of June, however it is expected to rise again in coming weeks. It is too early to tell whether it will increase far enough to have an adverse impact on rainfall.