Spring brings sunshine while La Nina uncertainty remains

Several days of 15 and 16-degrees lay ahead this week, with morning temperatures forecast to dip below zero just once, on Saturday.

It was a very wet month at the Canberra Airport in August with more than 116 millimeters falling, compared to a monthly average of 46 millimeters, since records began.

Mornings were one to two degrees warmer than typical throughout the month, except on August 24, when temperatures dropped to -6.3 degrees.

The Canberra Airport measured a wetter than average winter overall, with 156 millimeters falling, compared to an average of 128 millimeters over all years.

It was a fairly standard Canberra winter in terms of daily max temperatures, the exceptions were on July 14 when it didn't get above 6.8 and August 28 when it climbed to a balmy 18.7 degrees.

The Bureau has shied away from declaring another La Nina this spring, despite several other countries already having done so.

Wetter-than-usual weeks ahead remain at 70 per cent likelihood, while countries including the United States and Japan have already accepted their fate.

Almost all of Australia is likely to experience warmer than average nights, according to the bureau, while cooler days are likely for large parts of the mainland except the tropical north.

Dr Zoe Gillett, an ARC Centre of Excellence for Climate Extremes researcher, said even without the declaration spring looked wet for Canberra.

"Seasonal outlooks for September to December are suggesting above-average rainfall for eastern Australia, including in NSW and the ACT," she said.

"After two years of above-average rainfall, catchments are saturated and there is an increased risk of flooding.

"The possibility of more rain falling on already saturated catchments is concerning for communities still recovering from recent flooding events."

La Nina is a naturally occurring phenomenon whereby warm ocean water piles up around northern Australia and colder water rises to the surface off South America.

This leads to ocean circulation changes, consequently, warm rising air and rainfall increase in the western Pacific.

Dr Gillet said different countries use different thresholds and definitions to define La Nina.

"One way to measure La Nina is when the sea surface temperatures in the equatorial Pacific Ocean fall below a threshold for a sustained period of time.

She said the bureau uses a slightly higher threshold than other agencies, requiring the sea surface temperatures to be colder before a La Nina event is declared.

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Dr Lynette Bettio, a Bureau of Meteorology climatologist, said a positive Southern Annular Mode was also likely next month, pushing weather systems south and bringing wetter easterly winds to NSW.

"In northern Australia, the first rains of the wet season are likely be earlier than normal for much of Queensland and the Northern Territory."

Dr Bettio said parts of Western Australia and western Tasmania are likely to experience below average rainfall this spring.

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