Seasonal Climate Outlook July - September 2009
The Bureau of Meteorology released the rainfall outlook for the period July to September on 23 June 2009.
The outlook does not show a significant shift in the odds favouring drier than normal conditions for Victoria. The chances of exceeding the median rainfall are between 40% and 45% across most of the state, with between 45% and 55% in east Gippsland and between 35% and 40% for southwest Victoria.
The Bureau issued the ENSO Wrap-Up on 17 June 2009. The signs of a developing El Niño have strengthened during the past fortnight. The key indicators for this are a drop in the Southern Oscillation Index to −10, further warming of the Pacific and a strong decrease in the strength of the Trade Winds. Many computer models remain firm in their predictions of an El Niño event in 2009. This puts the odds of an El Niño at above 50%, which is more than double the normal risk of an event. However, it is still possible, though increasingly less likely, that the recent trends may stall without El Niño thresholds being reached.
Another adverse sign for southeastern Australian rainfall is the recent trend to positive values in the Indian Ocean Dipole as measured by the Dipole Mode Index.