Summer could be wet thanks to a La Nina expected to hit Victoria

IT could be a wet summer in Victoria if a La Nina shapes up as expected according to the Bureau of Meteorology. So what are the odds?

A LA Nina weather event may be on its way to Victoria and the eastern states by the end of the year, raising the possibility of a wetter-than-average summer.

That’s the word from the Bureau of Meteorology’s senior climatologist Dr Andrew Watkins who said there is a 50 per cent chance we will get a La Nina this summer.

But it’s not likely to be strong or long-lasting, he said.

David Jochinke on his farm at Murra Warra, 330km northwest of Melbourne, when a La Nina was expected to come last year. Photo: Aaron Francis

WHAT IS LA NIÑA?

The last La Nina, from 2010 to 2012, delivered widespread disastrous flooding in northern Victoria and Queensland.

Late last month, the Bureau of Meteorology declared a La Nina watch, meaning there is now a 50 per cent chance a La Nina may occur before the end of 2017.

“Now, 50 per cent mightn’t sound like a lot but it’s actually double the normal risk of having a La Nina,” Dr Watkins said.

“Typically, during the late spring and summer a La Nina would bring more rainfall, particularly to Queensland, but also the eastern states of Australia.

“We would expect to see warmer temperatures in the southeast and usually cooler temperatures up there in Queensland as we get more cloud cover and so on. Typically, you might see tropical cyclone numbers increase as well.”

A La Nina could bring rain to Melbourne this summer. Picture: Nicole Garmston

You might have to pull out your brolly out this summer. Picture: Nicole Garmston

Conditions in the Pacific Ocean are pointing to a La Nina forming but another climate driver, the Indian Ocean Dipole, is working against a La Nina and could moderate one if it occurs, Dr Watkins said.

At the moment, sea surface temperatures in the Indian Ocean are cooler and, while warm, Pacific Ocean waters aren’t as warm as in past La Nina events.

Dr Watkins says climate signals are not strongly in favour or against above-average rainfall in the east even if a La Nina forms, and it’s unlikely there will be more tropical cyclones than the 10 to 13 forecast for eastern Australia by the Bureau earlier this year.

“Normally it would mean that we see increased rainfall in eastern Australia, but this season, at the moment at least, the Indian Ocean is opposing that signal coming out of the Pacific Ocean,” he said.

“So, at the moment, our odds are still at the 50 per cent mark of getting above normal rain, so not really going for the extreme rains that we have seen during past La Nina events.”

Australia’s last La Nina, which followed the El Nino-driven Millennium Drought, was a doozy.

The 2010 to 2012 La Nina caused widespread rainfall from far northern Queensland to Tasmania, with deadly and devastating floods.

An aerial view of inundated properties after the Lodden River banks burst following days of torrential rain in area and widespread flooding in January 2011.

Building were flooded after days of torrential rain in Kerang during summer in 2011.

In Victoria, Charlton, Kerang and Carisbrook, near Maryborough, were among the towns hardest hit by the deluge.

This period combined a very strong La Nina cycle with favourably warm conditions in the Indian Ocean, delivering the wettest two-year period ever recorded in Australia.

“In 2010-12 we saw all the ducks lining up in the pond. This year, just the chance really … of just a weak and possibly short-lived La Nina event, whereas those other indicators are pretty neutral, really,” Dr Watkins says.

What to expect from the climate for the next three months:

Dr Watkins said the latest three-month climate outlook surge

sts day and night temperatures may be a little higher than average.

But there is no strong indication whether rainfall will vary far from the average.

SUN OR RAIN FOR VICTORIA’S SUMMER

What is a La Nina?

The El Nino Southern Oscillation (ENSO) is one of the world’s major climate drivers.

A range of weather features including sea surface temperatures in the tropical Pacific Ocean are tracked by the Bureau of Meteorology’s ENSO index.

ENSO has three basic cycles — neutral, La Nina and El Nino.

In neutral (more normal) conditions, trade winds blow from east to west across the tropical Pacific, causing warmer sea surface temperatures to pool in the west (to Australia’s north and east) and cooling the east, near Central America.

In an El Nino, the trade winds are disrupted, causing sea surface temperatures to cool in the west and grow much warmer in the east, reducing evaporation and cloud cover near Australia and, in many cases, leading to drought across eastern Australia.

For La Nina, those trade winds strengthen across the tropical Pacific, causing more warmer water to gather in the west, north of Australia, and in many cases, causing increased evaporation, rainfall and cyclone activity around eastern Australia.

But no two El Nino or La Nina events are the same, and in some cases weather patterns considered typical under those conditions don’t materialise.