Tuesday, December 5, 2023

State of play as spring blasts its way in

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Phil Duncan takes the country’s temperature and gauges its rainfall.
Reading Time: 3 minutes

By Phil Duncan, WeatherWatch

We are in the thick of spring now – the ultimate “hold onto your hat” weather as westerly blasts deliver cold fronts and short bursts of severe weather across the country.

Despite an uptick in complaints from people who missed the headline that an El Niño spring can be wetter and cooler for many western regions, the weather pattern is settling into a new more traditional westerly-driven flow. 

So the complaints we’re getting, are they accurate?  Let’s take a look at the state of the nation now that we’re in the middle of spring.

Soil Moisture
Much of New Zealand is in a healthy position soil moisture-wise – especially with so many worried about summer being drier. But the areas now showing up as driest are in the biggest rain shadow areas: Nelson and Marlborough. 

The west to southwest flow of winter means these two regions (and in particular Marlborough) can miss out on rain. And unlike their neighbours in Wellington and Wairarapa (who receive southerly rain), Nelson and Marlborough usually do not. 

For anyone wanting to track the progress of El Niño’s drier trend, Marlborough is a good place to start. But outside of Nelson and Marlborough every single other region is in a healthier set-up. 

There are a few spots in Canterbury that are drier than usual, but there are also large portions of eastern NZ wetter than average (Gisborne, northern Hawke’s Bay and, incredibly, Otago).

So far this month rainfall has been lower than average in Marlborough, most notably, followed closely by the South Canterbury/Otago area (and according to NIWA data western Southland too). 

Much of the North Island has had closer to normal falls thanks to more low pressure in the area bringing a more even spread of rain to various regions. 

But Wairarapa, Central Hawke’s Bay, Bay of Plenty and the Hauraki Plains have actually seen below normal rainfall according to public stats by NIWA.  The West Coast has seen the most amount of rain, although it has been excessive. The Indian Ocean Dipole (the Indian Ocean’s version of El Niño) may be limiting rain events recently in the Southern Ocean, which means the West Coast has below normal rainfall (for now). 

The ‘El Niño lean’ is starting to show up, where westerly winds push rain into the west, but eastern areas dry out more – especially the South Island.

Our mountains and ranges really become obvious when the airflow (a westerly lately) has become more one sided. The north-eastern corner of the South Island, from Nelson to Rangiora, has been sunniest. (Although the West Coast has enjoyed sunnier than normal weather it didn’t clock up the same bright sunny hours as its northeastern neighbours).

In the North Island East Cape wins the gold medal for bright sunshine hours, followed closely by Bay of Plenty. Gloomiest regions lately: No surprise, the western side of the North Island and much of Southland.

Very generally, the North Island has leaned cooler than average this October by a degree or so, while the South Island has leaned warmer by the same amount. This may even up more in the next two weeks.

NEW PODCAST ALERT: Farmers Weekly’s podcast series, El Niño Watch, tracks the potential impacts of the El Niño weather system on farming in rural New Zealand. Listen to the first episode below.

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