La Niña, the main cause behind Australia’s wet summer, has now ended, with ocean and weather conditions in the Pacific Ocean returning to normal during the past few weeks.
“As was expected during autumn, the 2011/2012 La Niña has now come to an end. Near average conditions have developed in the Pacific Ocean and will remain until at least winter,” says Tom Saunders, Senior Meteorologist at The Weather Channel.
“A few key indicators are used to make a call on the end of a La Niña event. Firstly, since the beginning of February, sea surface temperatures (SSTs) over the central equatorial Pacific have rapidly warmed, moving us from La Niña into neutral conditions.
“A second indicator is the Southern Oscillation Index (SOI), which measures the pressure difference between Tahiti and Darwin. Late last year the SOI reached +24, well above La Niña thresholds of about +8, but during February the SOI averaged only +2.5,” says Saunders.
“With Australia’s northern wet season also coming to an end, we can expect drier weather through most northern and central parts of the country during April and May. The exception is eastern New South Wales which often receives its heaviest rain during autumn, meaning La Niña’s demise will not necessarily bring the sunshine most Sydneysiders are hoping for.
“It is too early to forecast what phase the Pacific Ocean will move to in winter, we could remain in neutral, return to another La Niña or welcome back El Niño,” he concludes.
