Seasonal Climate Outlook - March 2011 to May 2011
The Bureau of Meteorology released its rainfall outlook for March to May 2011 on 24 February. The outlook favours drier than average conditions over southern Victoria, while average conditions are favoured over the rest of the State. The pattern of seasonal rainfall odds across Australia is a result of cool ocean temperature patterns from the current La Niña event in the Pacific Ocean.
The Bureau’s latest ENSO Wrap-Up, issued on 16 February, reports that the strong La Niña event which has dominated the Australian climate for the past nine months is showing signs of weakening. The 2010/11 event has been one of the strongest La Niña events on record. Pacific Ocean temperatures have increased, especially below the surface, while atmospheric indicators such as the Southern Oscillation Index (SOI), trade winds and cloud patterns have eased from their peaks reached in early January.
The life cycle of past La Niña events and long-range forecast models surveyed by the Bureau suggests the Pacific gradually warming during the southern autumn of 2011. All available climate models suggest further weakening of the La Niña is likely through autumn, with the most likely outcome of a return to neutral conditions by winter 2011. However, there remains a chance that the event may reform after autumn.
La Niña periods are generally associated with above normal rainfall during winter, spring and summer particularly across eastern and northern Australia. Tropical cyclone occurrence in northern Australia is typically higher than normal during the cyclone season (Nov-April), with February and March the peak.