Monday, February 26, 2024

Let’s play Wheel of Weather!

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February will bring even more variety to our famously changeable weather, Phil Duncan says.
The overall summary for the week ahead is more dry weather on the way for eastern regions, with wet weather in the west.
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Phil Duncan, WeatherWatch Analyst

There is a chance that weather forecasting is about to get even trickier in New Zealand – and it’s already hard enough as it is! 

The weather pattern coming up in February is one of heat and humidity from the north, mixed in with highs, westerlies and lows from the south. 

Our location on earth means we have two “main lanes” of weather traffic. The Southern Ocean is the “motorway” – the biggest of them all – tracking west to east each day with strong westerlies.  

The second lane of weather traffic comes from the warmer Tasman Sea and sub-tropical zones to our north and west – this is like a main highway that feeds into the Southern Ocean “motorway” of weather.  

This makes NZ a bit like an intersection, where the weather systems meet, join, crash into each other and cause congestion. Our mountains and ranges can then act like a speed bump – slowing systems down as they move into them, but, like humans in a car, can also rapidly speed up once over the speed bump. 

This colourful analogy is to try to explain how the weather tends to come at us – and going into February there is far more variety in the forecast than we might normally expect.

There are now significant marine heatwaves – widespread across the Tasman Sea, Coral Sea and north of New Zealand in the tropics too. This is traditionally the opposite of what happens in El Niño. 

Add on top of that new data suggesting the Hunga Tonga–Hunga Ha’apai eruption two years ago may have pushed moisture so high up in our atmosphere it’s stuck there, creating a glasshouse effect that has warmed conditions by half a degree, and now you’ve got the perfect recipe for more surprise storms and lows. 

It’s a messy pattern – one that still sees some powerful highs in the mix. Summer is NOT over. El Niño IS still here and we WILL still be seeing dry areas get drier. But the highs and lows are dancing together and means we may see some swings in temperatures, humidity, and unstable wet and dry.

A week is a long time in weather forecasting so this may not pan out exactly as I’m writing or as the image suggests – but what it does suggest is just how messy the weather pattern is for our part of the world. 

Certainly no great El Niño highs stubbornly parked over or near us. Storms across the tropics, storms in the Southern Ocean, highs to the west of us, highs to the east – and here I am, stuck in the middle with you. 

Upcoming Highlights

• Variety of wind flows for NZ this week, from a low with sub-tropical connections in the north to westerlies later in the week

• Southern Ocean storm possible south of NZ

• New Tropical Cyclone risks north of NZ

• High pressure tries to reach NZ this weekend

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