Seasonal Climate Outlook October - December 2009
The Bureau of Meteorology released its rainfall outlook for October to December on 22 September. The outlook reports a moderate to strong shift in the odds favouring drier than normal conditions for most of Victoria throughout the December quarter. The chance of exceeding the median rainfall for the season across the southern regions of the state is between 25% and 40%. For the majority of northern Victoria, the chance is between 30% and 45%.
The Bureau issued its latest ENSO Wrap-Up on 30 September 2009. The Bureau continues to report the overall likelihood of a developing, yet “unusual”, El Niño event during 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 irregular nature of the current conditions has been related to the unusual warming patterns across the Pacific ocean. While warm ocean temperatures in parts of the Pacific are consistent with El Niño conditions, temperatures in other areas generally cooler in an El Niño year are also above average. This could be the reason for temperature, cloud and wind patterns that have not reflected typical El Niño trends.
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.