The majority of dynamical models surveyed by the Bureau of Meteorology suggest that the central Pacific Ocean is likely to continue to cool over the next few months with a return to neutral values by the southern hemisphere autumn. All models predict the event will peak in the southern hemisphere summer. Monthly summer raifall is expected to be above average.

In last year’s strong La Niña episode only three were recorded as follows:-

Severe Tropical Cyclone Yasi ………………………30 January – 3 February 2011 

Tropical Cyclone Anthony ……………………………22 – 31 January 2011

Severe Tropical Cyclone Zelia ………….………….14 – 18 January 2011

“The Southern Oscillation Index, a key climate driver, was (positive) 11.7 in September this year, compared with (positive) 25 at the same time last year. While this may be weaker than the last, this doesn’t mean we can expect fewer tropical cyclones than the previous season. In other words, we can’t afford to be complacent,” said Dr Watkins.

The current La Nina may be weaker but still means the monthly rainfall is likely to be above average.

The Maleny Weather Station rainfall recorded during the life of the La Niña episode was 3278mm. The 117 year average for the same 10 month period is 1747mm.

The 2010−11 La Niña event has ended, with climate indicators of the El Niño – Southern Oscillation (ENSO) having returned to average levels. Climate models surveyed by the Bureau of Meteorology suggest that the Pacific Ocean will continue to warm over the coming months, with neutral conditions likely to persist through the austral winter; that is, neither La Niña nor El Niño.

After lagging for several months, atmospheric indicators of ENSO such as pressure patterns, cloudiness and the trade winds, have responded to warming in the Pacific Ocean. The warming in the Pacific Ocean and changes in the atmosphere are consistent with the life cycle of past La Niña events, most of which lasted 9-12 months before declining during the southern autumn.

The influence of the Indian Ocean Dipole (IOD) on Australian rainfall is currently neutral. A weakly positive IOD event has been forecast to develop during winter. In the past, positive IOD events have been associated with drier conditions over parts of Australia, particularly in the southeast, during the winter and spring seasons.

Signs of a developing La Niña emerged during autumn 2010 as the Pacific cooled rapidly at the end of the 2009-10 El Niño. By July, La Niña conditions were established and most of Australia experienced significantly higher than average rainfall over the next eight months. Peaking between late 2010 and early 2011, this La Niña event was one of the strongest observed, in a record dating from the late 1800s. Record high rainfall occurred across much of northern and eastern Australia during this event, leading to widespread flooding in many regions between September 2010 and February 2011.

All climate indicators remain beyond La Niña thresholds. The tropical Pacific Ocean remains much cooler than average for this time of year, with temperatures below the surface up to 4 °C below normal in central and eastern parts (comparable to the La Niña event of 1988/9, when Maleny’s rainfall from Dec to April was 2607mm, over double the average of 1288mm). Trade winds are stronger than average, while cloud patterns continue to show a typical La Niña signature with suppressed cloudiness in tropical areas near the dateline. The Southern Oscillation Index (SOI) value for December of +27 is the highest December SOI value on record, as well as being the highest value for any month since November 1973.

La Niña periods are generally associated with above normal winter, spring and summer rainfall, particularly over eastern and northern Australia. The current event has contributed to 2010 being Australia’s the third wettest year on record, and Queensland having its wettest December on record. During La Niña periods, Tropical Cyclone occurrence for northern Australia is typically higher than normal during the cyclone season (November-April), while summer daytime temperatures are often below average, particularly in areas experiencing higher than normal rainfall.

La Niña periods are usually, but not always, associated with above normal rainfall during the second half of the year across large parts of Australia, most notably eastern and northern regions. Night time temperatures are historically warmer than average and Tropical Cyclone occurrence for northern Australia is typically higher than normal during the cyclone season (November-April).

 Last Week’s Riddle: Why did the woman go outdoors with her purse open? Answer: Because she expected some change in the weather.

 This week’s riddle: What gets wetter the more it dries?