Seasonal Climate Outlook - January 2011 to March 2011
The Bureau of Meteorology released its rainfall outlook for January to March 2011 on 17 December. Wetter than average conditions are favoured for eastern New South Wales. The odds for Victoria are closer to neutral (between 50 and 60%), with above average rainfall being as likely as below average rainfall. The pattern of seasonal rainfall odds across Australia is a result of cool conditions in the equatorial Pacific Ocean associated with the current La Niña.
The Bureau’s latest ENSO Wrap-Up issued on 22 December reports that La Niña conditions remain firmly in place in the tropical Pacific. Long range model outlooks suggest the La Niña event may be nearing its peak. A gradual decline in the conditions is likely, with the event expected to persist through the first quarter of 2011.
All ENSO indicators continue to exceed La Niña thresholds. Despite a slight warming of the tropical Pacific Ocean in the past fortnight, sub-surface temperatures in the eastern and central Pacific remain up to 4 degrees cooler than the long-term average. As a result, the Southern Oscillation Index (SOI) remains strongly positive, the trade winds remain stronger than average across the central and western equatorial Pacific and cloudiness near the date-line remains suppressed.
La Niña periods are generally associated with above normal rainfall during the second half of the year across large parts of Australia, most notably eastern and northern regions. Tropical cyclone occurrence in northern Australia is typically higher than normal during the cyclone season (Nov-April).
The Indian Ocean Dipole (IOD) is currently neutral. The influence of the IOD on rainfall in Australia between December and April is typically limited.