‘High-risk’: BOM warns of summer of wild weather including severe floods and cyclones

One of Australia’s top climate outlook experts says Queensland is in for a summer of “high-risk” weather, regardless of whether a La Nina is officially declared.

Queenslanders have been told to forget the hype surrounding a potential La Nina declaration and focus on the inevitable wet summer ahead which will likely involve severe floods and cyclones.

Head of long range forecasting at the Bureau of Meteorology Dr Andrew Watkins said Queensland will experience “high risk” weather from October onwards regardless of an official La Nina declaration.

He said the Bureau's carefully measured climate outlook reports will not change if a La Nina is declared and should be relied upon for the most accurate rainfall and severe weather risk predictions.

“It’s not as though when the Bureau declares La Nina, a switch is flipped and it’s suddenly more wet, it’s already going to be more wet,” Dr Watkins said.

“La Nina wont change our outlooks, those things are factored in already and all of our outlooks are showing wetter than average conditions.

“The way the (weather) systems interact, that’s important, not the name La Nina itself because no two summers are going to be the same, this year could be better or worse but there is an elevated risk of flooding due to the wet landscape.”

Dr Watkins explains that to declare a La Nina event, certain weather patterns need to align and “lock in”.

“La Nina is when we start observing warm water in the western tropical pacific but cooler than normal water in the eastern central pacific,” Dr Watkins said.

“The weather patterns, cloud, moisture, follow that warm water as it moves west towards Australia and you get a shift in weather patterns because of temperatures and then the ocean and atmosphere start reinforcing each other.

“What we’re looking for in that (La Nina) criteria is a cooling in the central tropical pacific, changes in the trade winds and changes in the pressure patterns and cloud that sort of shows the atmosphere and ocean are locked in together for a La Nina.

“The last thing is looking at seven international climate models, and assess whether that pattern is likely to stay locked in for three months.”

Because a La Nina event is a global weather event cycling between South America, across to Australia, up through Asia and back across to North America, different countries declare the La Nina “lock in” at different times.

Dr Watkins said forecasters should have “a good idea” of La Nina potential by October, which is generally the start month of Australia’s “severe” or “high-risk” weather season.

“What’s happening with this high risk seasons is it starts with topical air in the northern hemisphere, which will slowly move south,” Dr Watkins said.

“Once we see it come into Australia then you get weather systems from the south mixing with ones from the north and you tend to get your bigger rain events.

“Systems coming in from Northern Australia tend to affect inland Queensland whereas La Nina and SAM can affect those coastal Queensland areas, so there’s really no spot that‘s more or less at risk of flooding.

“From October onwards is when we’ll start releasing more general information for the remainder of Spring or Summer ahead of that higher risk weather, like cyclones and flooding.”

Should the Pacific Ocean warm instead of cool and cloud and wind conditions weaken, the Bureau could revert back to a La Nina watch however, history shows that under the current weather conditions, a La Nina return is 70 per cent likely.

“In any given year there’s a 20-25 per cent chance you’d get a La Nina,” Dr Watkins said.

“The number 70 per cent, goes back to that expert criteria, and comes from looking back in history … as in 70 per cent of the time we’ve been on alert we would have had a La Nina follow, that’s where that number comes from.

“What’s happening in the tropical, things are cooling and that’s why we’ve gone to 70 per cent along the equator, but if it turns around we could go back to watch.”