Seasonal Climate Outlook September - November 2009
The Bureau of Meteorology released its rainfall outlook for September to November on 26 August. The outlook reports a moderate to strong shift in the odds favouring drier than normal conditions for most of Victoria. The chance of exceeding the median rainfall for spring across most of the state is 35%. In far northwestern Victoria, the chance is below 30%, while in the northeast corner of the state, the chance is at best 40%.
The Bureau issued its latest ENSO Wrap-Up on 19 August 2009. The Bureau continues to report the overall likelihood of a developing El Niño event during 2009, however, recent conditions have not strengthened this forecast. The coupling between the ocean and atmosphere necessary to intensify and maintain an El Niño event has not yet occurred. This is demonstrated by a neutral Southern Oscillation Index (SOI), and the cooling of subsurface ocean temperatures in some areas of the Pacific throughout July and August. Typically, SOI values would be negative, and subsurface temperatures warmer during an El Niño event. Nevertheless, modelling predicts that conditions supporting an El Niño event will peak towards the end of the year. 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) is currently around zero, and is expected to remain neutral over the coming months. A positive IOD is typically associated with decreased rainfall across parts of central and southern Australia.