Seasonal Climate Outlook - November 2011 to January 2012
On 25 October, the Bureau of Meteorology released the rainfall outlook for the period November 2011 to January 2012. It shows: 1) a wetter season is likely for most of south-eastern Australia; 2) the strongest probabilities occur in north-eastern NSW; and 3) no strong signal for Victoria and Tasmania. A persistently warm Indian Ocean is the main driver behind this outlook, although it is also consistent with the developing La Niña in the Pacific Ocean. Over Victoria, the chances of a drier or wetter November to January are roughly equal. The next outlook report is due on 22 November 2011.
The Bureau’s latest ENSO Wrap-Up, issued on 26 October, reports the tropical Pacific Ocean is now in the early stages of a late-forming La Niña event. Pacific Ocean temperatures have slowly cooled during spring and are now at La Niña levels. Key atmospheric indicators such as trade winds, cloud and the Southern Oscillation Index (SOI), are also close to, or have exceeded, La Niña thresholds. Computer models surveyed by the Bureau suggest further strengthening of the event over summer; however, current observations and model predictions indicate that this La Niña is likely to be weaker than the strong 2010-11 event. La Niña events raise the odds of above average rainfall across northern and eastern Australia, but do not guarantee it. Oceans surrounding Australia’s north are currently close to or cooler than average, which is less favourable for widespread rainfall than at this time in 2010, when they were much warmer than normal. Similarly, the latest observations from the Indian Ocean show a positive dipole event. A positive dipole event increases the chance of below average rainfall over south-eastern and central Australia during spring.