If the Australian bush fires ripping through the continent's southeast states endure until forecast rain in late January, then today's hazy orange smoke in the Auckland sky will likely be a common occurrence.
It's all dependent on an unbroken northwest flow of wind, which has meant the 5.5 million square kilometre expanse of thick smoke drifting off Australia has made its way to New Zealand largely undisturbed.
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A northwest flow indicates the direction the wind is coming from, and it lines up Australian states New South Wales and Victoria with New Zealand fairly directly.
"Yesterday, we had a northwest flow which meant that all the smoke was being drawn across the Tasman Sea over the South Island and because that flow was unbroken it was very thick," MetService meteorologist Tahlia Crabtree said.
"Nothing much was mixing it up and that's why you saw all these incredible images of the sky being quite hazy and orange over the South Island.
TRUE COLOUR SATELLITE SHOWS SMOKE FROM AUSTRALIAN FIRES As a meteorologist, we often look to satellite imagery over the...
Posted by MetService New Zealand on Monday, 30 December 2019
Overnight, another front up the South Island moved the smoke over much of the North Island, but it will likely disperse entirely from New Zealand over the next 24 hours.
"There's a southwest change over the South Island today with a lot of clear air behind that," Crabtree said.
"So throughout today and tomorrow you can expect all that smoke to clear across the whole country."
The actual phenomenon that creates the orange haze over Auckland today is called cloud condensation nuclei (CCNs).
Smoke from the #AustralianFires reach Auckland, NZ and the sun turns red 😢#bushfiresNSW pic.twitter.com/UdDSaCM2TM
— Mariah Cousins (@MariaCousins1) January 1, 2020
Looks like it's Auckland's turn to lose the sun#AustralianFires pic.twitter.com/Qri6FEFYoY
— Keith Miller (@keith_miller_nz) January 1, 2020
CCNs are small particles typically 1/100th the size of a cloud droplet which water vapour can condense on.
The smoke particles in the atmosphere above the North Island are acting as this non-gaseous surface to make the transition from vapour to a liquid.
"They're little particles in the air and they're big enough that they can interact with the light from the sun which is why it ends up looking quite hazy, scattering the light," Crabtree said.
"The brown or orange tinge is due to the fact it tends to scatter light at the blue end of the visible light spectrum which means eventually the reds and oranges are more significant.
"Especially at sunrise and sunset there is more of the troposphere, the upper atmosphere, that the light has to travel through, and if there's a lot of smoke there's a lot more scattering."
In large amounts as is currently being seen in Australia smoke particles can also have a large effect on the weather, causing enough cloud for rain to fall or even thunderstorms - with the associated cloud called pyrocumulonimbus.
Because northwest flows across the Tasman are relatively common, the hazy orange skies created by smoke CCNs may be repeated for Kiwis across January.
"I would say very likely we will continue to see smoke coming across NZ. The extent of it will just depend on what the winds are doing across the Tasman Sea," Crabtree said.
"We tend to get situations with northwest flows quite regularly and a northwest flow like that which brought across all that smoke, we can expect something like that again.
"I'm not sure if we'll get something as bad but we'll definitely continue to see smoke coming across New Zealand throughout the period where the fires are going.
"Since they've started, we've had periods where smoke was being brought across the Tasman, it's just the weather was changing a little more quickly so all of the smoke tended to disperse or move away quickly before it could affect our skies."
Yesterday, South Island residents woke to an even more pronounced yellow haze as a thicker smoke hit regions directly from across the Tasman Sea.
Drivers in Dunedin reported still using their headlights as of 9am yesterday.
One asthma sufferer told the Otago Daily Times they would not be venturing outside today because of the risk the smoke would cause respiratory issues.
Paul Bonner told the ODT that smoke was covering mountain tops in Queenstown and made for hazy-yellow skies in Cromwell.
He said smoke could be smelt and tasted in Queenstown, which could be problematic for asthmatics.
Residents in Christchurch and Akaroa also shared images of yellow-hazy skies.
The geographical area which the Australian fires have covered is also being remarked upon by global media outlets.
As of earlier this week, at least 4.4 million hectares has been burned in NSW, Queensland, South Australia and Victoria since the start of the 2019 fire season.
Overlaid over the North Island, the area of the fires in Australia would cover well north of Auckland and spread south beyond Hamilton.
It also spreads over a vast area of the Tasman Sea and the Pacific Ocean.
An incredible sight from the edge of GOES-17 satellite's view today with smoke from the Australian fires clearly seen advecting in from the northwest. This true colour image simulates what the eye would see by using 3 'wavelength bands' taken by the satellite stacked together ^AC pic.twitter.com/b3uFGLRUva
— MetService (@MetService) December 31, 2019
The Australian forecast for relief to the bushfire-prone conditions is also not promising.
Drought-stricken areas of Australia's east are predicted to have below average rainfall for the next three months.
NSW Rural Fire Service Commissioner Shane Fitzsimmons said "worsening conditions" would return again this Saturday.
Victorian Emergency Management Commissioner Andrew Crisp described this Saturday as a "spike day" in the already unprecedented Australian bushfire season.
The temperature is forecast to reach 43C on Saturday in southern coastal towns of New South Wales such as Nowra and down towards Bega. Over the Victorian border, it could tip 41C in Mallacoota.
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