Batten down the hatches, more La Nina storms likely

Monday, February 04, 2008

Dubbo, NSW, has been told: 'batten down the hatches' - there are more storms on the way over the next four days.
The storms are the direct result of an entrenched La Nina summer in many parts of the eastern states, bringing above-average rainfall.

Other storms around Dubbo have already dropped 390mm of rain since the start of November, with two recent severe thunderstorms on consecutive days.

Head of Charles Sturt University’s School of Rural Management and climatologist, Kevin Parton, says violent evening storms and torrential rains, often associated with tropical climates, have followed hot and humid days.

In recent years, regional NSW has been experiencing the worst drought on record.

But a switch from El Nino to La Nina patterns has coincided with above-average summer rainfall.

The rain since November is almost 10 times the amount received during the same three-month period in 2006-07, when just 39mm fell.

The average for that period is 152mm.

Professor Parton says,“Around November, sea surface temperatures and other indicators flipped from El Nino conditions to La Nina.

“Higher sea surface temperatures off the east coast of Australia have generated pressure systems that cause air flows generating the kind of weather we are having now.

“The current air stream is typical of La Nina.”

Professor Parton said weather system models may not stretch as far as predicting winter rain patterns, but he believes initial projections look promising.

“During early spring, there was a consensus among several important climate modelling groups that there would be higher than average rainfall this summer,” Professor Parton said.

“That consensus was absolutely right.

“But now some groups are saying La Nina conditions will last and others say it won’t.

“The Southern Oscillation Index (SOI) models are based on three-month predictions and they are more reliable at some times of the year than at others.

“There are indications there is a likelihood of above average rainfall in autumn.

“But the best predictability is during winter and the time to check the predictions is at the end of April or start of May.”

Professor Parton estimates that in the longer term there will continue to be more and more prolonged El Nino events, normally associated with dry weather in eastern Australia.

“All climatologists are aware that these are significant cycles affecting weather patterns,” he said.

“The important thing that they should start to look at is working out how these cycles are affected by climate change.”

SOURCE: Daily Liberal, Dubbo, NSW