LA NINA has decided to make an appearance just in time for Christmas. If you’re making plans, this is what you need to know.
Bureau of Meteorology: Understanding ENSO
JUST in time for Christmas, the weather has
gifted Australia an early present with the declaration the country is
now officially in the grip of La Nina.
But
whether the La Nina climate driver will be a much cherished Christmas
present, or the equivalent of yet another pair of socks, will depend
very much on where you live.
While it’s a bit early to forecast exactly what the weather will be like on Christmas Day, La Nina is leading the meteorological boffins to firm up their thoughts on December’s weather — as well as for the rest of summer.
“We’re going to experience La Nina this Christmas. In December, the
odds are over 60 per cent for a wetter, colder month in southern
Queensland, NSW, Victoria, Tasmania and the populated areas of South
Australia,” Dr Andrew Watkins, the Bureau of Meteorology’s (BoM) Manager
of Long Range Forecasts told news.com.au.
It could be cloudier too, with less blue skies. However, the most southerly capitals also have an increased chance of longer, warmer spells this Christmas. But these are unlikely to be, “short, sharp extreme temperature” spikes, Dr Watkins said.
The Australian Bureau’s La Nina confirmation came a bit later than
the organisation’s US counterparts which require equatorial sea surface
temperature to sink to 0.5C below average. The bar is higher, and
colder`, for the BoM which says the same seas must be 0.8C below.
But the outcome for Australia is the same. During a La Nina, which has counter effects to El Nino, while equatorial seas get cooler, the waters north of Australia warm up. That helps to produce rising air, clouds and rainfall over northern and eastern parts.
“Typically, the La Nina impacts we see is that summers are cooler and a bit wetter,” Dr Watkins said.
“But this year’s a bit different as the La Nina is looking weak and it’s starting much later which is quiet unusual.”
The late La Nina, as well as colder than expected seas around
Northern Australia, means the effects are unlikely to be at the extreme
end of the scale and could even weaken further, bringing conditions
closer to average.
Dr Watkins said several effects of La Nina were already being felt. The heatwaves and rains in Victoria and Tasmania had La Nina written all over them.
But there were subtler signs too, which could mean Bondi may not be the best location for a Christmas Day dip.
“Summer swimming has come early around Tasmania and Victoria with waters 3C warmer than usual but around Sydney, seas are 3C cooler so it’s a bit chilly. Port Phillip Bay is actually warmer than Sydney Harbour,” he said.
This isn’t unheard of during a La Nina with winds coming off the Tasman Sea cooling down Sydney and Brisbane. Melbourne, Adelaide and Hobart miss out on these while also being affected by slow moving warm weather systems lolloping lazily across the continent.
The Bureau will release its official Christmas Day forecast on 18 December, but here’s the information we have so far on how La Nina could affect the capitals over the festive season.
BRISBANE
29.1C is the average for December with around 133mm of rain. The weak La Nina could see those highs decrease around Christmas time with increased rainfall.
SYDNEY
Around 90mm of rain falls in Sydney during a typical Christmas month with 25C the average maximum. Like Brisbane, La Nina could dampen the festive party and bring the maximums down.
CANBERRA
The nation’s capital could see lower than the December average of 26.3C but there’s no need to pack away the barbecue just yet; it could still be a very pleasant Christmas Day.
MELBOURNE
The average rainfall is 59mm in December but just a week into the month, and after a wild weekend of rain, a full 73.4mm has fallen.
“December already has a bit more of a La Nina feel to it,” said Dr Watkins.
However, the Victorian capital could yet see some Yuletide warm spells similar to what the city saw in late November.
HOBART
Dr Watkins said Hobart’s recent hot run, where temperatures climbed above 25C on six consecutive days was “a classic La Nina spell”.
Even more so than Melbourne, Hobart’s rainfall has been off the scale. The 85cm the city has seen so far in December is eight times the average for the entire month.
La Nina could see more falls but with some strings of hot days over the festive period.
ADELAIDE
Average conditions are expected for Adelaide in the run up to Christmas, possibly even slightly below the festive average of about 27C.
PERTH
There isn't a strong swing to either exceptionally dry or wet conditions in WA but Dr Watkins said there was a 70-75 per cent chance Perth would see a drier than average December.
“La Nina and El Nino have less of an impact (in WA); it’s a bit more influenced by what’s happening in the eastern Indian Ocean. At the moment, the ocean is slightly cooler than normal which is pretty abnormal and the opposite of what we expect to happen.”
DARWIN
Where’s the monsoon? That’s the question in the Top End. Normally at this time of year there would be signs of the monsoon forming but it currently remains north of the equator. Yet, it could still make an appearance in time to dampen Christmas lunch.
Monthly rainfall totals can be quite variable during the wet season, for example in Darwin the average December rainfall is 254mm but the highest recorded was at 665mm in 1974 and the lowest just 19mm in 1991. The weak La Nina is expected to have a minimal effect on rainfall.
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While it’s a bit early to forecast exactly what the weather will be like on Christmas Day, La Nina is leading the meteorological boffins to firm up their thoughts on December’s weather — as well as for the rest of summer.
 |
La Nina has been declared, now sea temperatures have
cooled to -0.8C below average in the equatorial Pacific. Picture: Bureau
of Meteorology. Source:Supplied
|
It could be cloudier too, with less blue skies. However, the most southerly capitals also have an increased chance of longer, warmer spells this Christmas. But these are unlikely to be, “short, sharp extreme temperature” spikes, Dr Watkins said.
 |
La Nina sees generally cooler waters in the equatorial region but warm waters around Indonesia. Picture: Bureau of Meteorology Source:Supplied
|
But the outcome for Australia is the same. During a La Nina, which has counter effects to El Nino, while equatorial seas get cooler, the waters north of Australia warm up. That helps to produce rising air, clouds and rainfall over northern and eastern parts.
“Typically, the La Nina impacts we see is that summers are cooler and a bit wetter,” Dr Watkins said.
“But this year’s a bit different as the La Nina is looking weak and it’s starting much later which is quiet unusual.”
 |
Looking forward to this on Christmas Day in Bondi? Picture: Dylan Robinson Source:News Corp Australia
|
 |
There’s a chance it could be more like this in Bondi over Christmas. Source:News Limited
|
Dr Watkins said several effects of La Nina were already being felt. The heatwaves and rains in Victoria and Tasmania had La Nina written all over them.
But there were subtler signs too, which could mean Bondi may not be the best location for a Christmas Day dip.
“Summer swimming has come early around Tasmania and Victoria with waters 3C warmer than usual but around Sydney, seas are 3C cooler so it’s a bit chilly. Port Phillip Bay is actually warmer than Sydney Harbour,” he said.
This isn’t unheard of during a La Nina with winds coming off the Tasman Sea cooling down Sydney and Brisbane. Melbourne, Adelaide and Hobart miss out on these while also being affected by slow moving warm weather systems lolloping lazily across the continent.
The Bureau will release its official Christmas Day forecast on 18 December, but here’s the information we have so far on how La Nina could affect the capitals over the festive season.
 |
Sea surface temperatures around Victoria and Tasmania are warmer than around Sydney. Picture: Bureau of Meteorology. Source:Supplied
|
29.1C is the average for December with around 133mm of rain. The weak La Nina could see those highs decrease around Christmas time with increased rainfall.
SYDNEY
Around 90mm of rain falls in Sydney during a typical Christmas month with 25C the average maximum. Like Brisbane, La Nina could dampen the festive party and bring the maximums down.
CANBERRA
The nation’s capital could see lower than the December average of 26.3C but there’s no need to pack away the barbecue just yet; it could still be a very pleasant Christmas Day.
MELBOURNE
The average rainfall is 59mm in December but just a week into the month, and after a wild weekend of rain, a full 73.4mm has fallen.
“December already has a bit more of a La Nina feel to it,” said Dr Watkins.
However, the Victorian capital could yet see some Yuletide warm spells similar to what the city saw in late November.
HOBART
Dr Watkins said Hobart’s recent hot run, where temperatures climbed above 25C on six consecutive days was “a classic La Nina spell”.
Even more so than Melbourne, Hobart’s rainfall has been off the scale. The 85cm the city has seen so far in December is eight times the average for the entire month.
La Nina could see more falls but with some strings of hot days over the festive period.
ADELAIDE
Average conditions are expected for Adelaide in the run up to Christmas, possibly even slightly below the festive average of about 27C.
 |
It could be a dry Christmas in WA such as here at Cottesloe beach. Photo: Alamy Source:Alamy
|
There isn't a strong swing to either exceptionally dry or wet conditions in WA but Dr Watkins said there was a 70-75 per cent chance Perth would see a drier than average December.
“La Nina and El Nino have less of an impact (in WA); it’s a bit more influenced by what’s happening in the eastern Indian Ocean. At the moment, the ocean is slightly cooler than normal which is pretty abnormal and the opposite of what we expect to happen.”
DARWIN
Where’s the monsoon? That’s the question in the Top End. Normally at this time of year there would be signs of the monsoon forming but it currently remains north of the equator. Yet, it could still make an appearance in time to dampen Christmas lunch.
Monthly rainfall totals can be quite variable during the wet season, for example in Darwin the average December rainfall is 254mm but the highest recorded was at 665mm in 1974 and the lowest just 19mm in 1991. The weak La Nina is expected to have a minimal effect on rainfall.
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