Saturday, December 2, 2023

El Niño very likely forming – but not yet affecting us

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Models show its highly likely tropical Pacific Ocean temperatures will reach El Niño thresholds during our winter.
All international climate models indicate it is highly likely that temperatures in the tropical Pacific Ocean will reach El Niño thresholds during our winter.
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By Phil Duncan, WeatherWatch senior forecaster

El Niño may be building but Australia’s Bureau of Meteorology, a respected climate forecaster for our part of the world, says – as it has done since two weeks ago – that there is still little response in the atmosphere. 

So despite being in an official “El Niño Watch”, the Pacific Ocean is currently considered “ENSO-Neutral”, which means it’s technically neither La Niña or El Niño at the moment. 

Currently all international climate models indicate it is highly likely that temperatures in the tropical Pacific Ocean will reach El Niño thresholds during our winter – but for an El Niño to be declared an atmospheric response is also required – for example a shift in trade winds, high pressure zones, and cloudiness in the Pacific. 

Bureau of Meteorology (BoM) scientists say the risk of El Niño forming this year is twice the normal chance. 

In our part of the world El Niño typically limits rainfall in eastern Australia during winter and spring. This is due to a significant uptick in high pressure zones parked over the eastern side of Australia and into the Tasman Sea. 

This then impacts New Zealand, with those highs often blocking rain-making events between Australia and NZ  and encouraging more of a west-to-southwest flow for our nation. This lifts cloud and rainfall for the South Island’s west and usually more cloud (but not more rain) for the western side of the North Island. 

Many other places can be drier and hotter inland and towards the east – and yes, El Niño does increase the risk of droughts.

But as we’ve said before, it’s important to remember that El Niño is not made in a perfectly calm laboratory with scientists and white coats. The Southern Ocean storms and Roaring Forties can make it harder to confirm how NZ is affected. 

It’s worth noting we just had three consecutive La Niña events and yet only one of them – the last one – felt like an actual La Niña weather pattern for NZ. The previous two brought drought to the North Island, which proves NZ can buck the trend.

If we look to our local NZ/Australia weather patterns we are certainly seeing some hints of El Niño forming – mainly in the form of large high pressure zones, which have been smothering Australia throughout May and as we go into June. This is keeping places like Queensland and New South Wales especially dry. 

There are a few hints in our weather pattern that El Niño is slowly forming with these highs increasing and drifting further eastwards into the NZ area. 

Highlights this week

• Powerful high pressure (1040hPa) east of NZ slowly moves away

• Westerly quarter winds kick off this week (thanks to a storm in the Southern Ocean at 940hPa)

• June to kick off with high pressure moving in from the Tasman Sea

• Drier than average in the east

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