Saturday, December 9, 2023

Records fall as NZ’s autumn temperatures soar

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NZ is such a small country that one big high or low can make us feel like something much bigger is going on.
The past few big highs have all slowed down east of NZ and encouraged windy nor’easters and sub-tropical airflows.
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By Philip Duncan, WeatherWatch

In line with recent forecasts, a large portion of New Zealand was over 2degC above normal in April and now May is kicking off well above normal, temperature-wise, all thanks to an enormous high pressure zone to the east of the country. 

Earlier this week, places like Otago and Southland were over 8degC above normal for this time of year. On May 3 Invercargill Airport had a high of 22.7degC and Queenstown Airport 22.4degC – making them the warmest May temperatures on record for both those stations. Both records were smashed by over 1degC.

In the upper North Island, overnight lows have been closer to 20degC for the second week running, with humidity in Auckland region hovering around 85-100% for an entire week. Last Wednesday, further south, Whanganui reached 25.3degC, breaking the previous May record of 24.7degC set only two days before. MetService says records there go back to 1978. 

If La Niña is over, why does it still feel like La Niña? You have to remember that La Niña is measured in the equatorial Pacific Ocean, well away from NZ. Indicators there are very much out of La Niña and leaning towards El Niño with an official “El Niño Watch” now in force.

But as we’ve been saying for several weeks, La Niña has finished and NZ is in a neutral period – where anything can happen. So, locally around NZ we have been stuck in our own wetter, warmer, set-up. You only have to go to Australia to notice they are in a more classic autumn weather pattern. Both nations have one thing in common – huge high pressure zones moving through. The past few big highs have all slowed down east of NZ (more like La Niña) and encouraged windy nor’easters, sub-tropical airflows and “Groundhog Day weather” (where it feels the same every day when you wake up!). 

Another enormous high pressure zone will be coming from Australia by next weekend.

NZ is such a small country that one big high or low can make us feel like something much bigger is going on, but in reality the luck of the draw of highs and lows sometimes means we can have a few weeks of warm and wet, or a few weeks of stormy and cold – or maybe something in the middle. Sea surface temperatures around NZ also remain above normal by a couple of degrees, which adds a little extra warmth in coastal areas overnight.

But we are in autumn and if Aussie is getting cold changes, NZ will too – and one should arrive next week, bringing a burst of snow to the South Island ranges and finally an end (for now) of those sub-tropical northerlies.

Highlights for next week:

• Daytime highs may struggle to reach over 10degC in the deep south on Wednesday

• A temperature drop for most of NZ by the end of this week

• Humidity drops below 80% in upper North Island for first time in a week

• Another enormous high pressure zone coming from Aussie by weekend

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