Friday, February 23, 2024

The next month’s weather explained as a canvas

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It helps to think of the weather in the month ahead as a canvas, says Phil Duncan. Now imagine there’s a brush with blue paint…
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By Phil Duncan, WeatherWatch

Imagine the month ahead is a canvas. El Niño is the base colour – let’s go with orange. 

So an entire canvas of orange signifies the weather pattern we were expecting over New Zealand and Australia this summer. 

Now imagine someone’s taken hold of a brush with blue paint and flicked it, and the canvas is splattered with blue blobs. That represents the surprise rain and downpours that have hit parts of Australia and NZ this summer. 

I wanted to paint this picture in your mind as, to me, it’s a way of understanding the two layers of weather we’ve got going on. 

The foundation of our summer is that it should have more westerlies and larger dry areas to the east or inland. In many places this is now happening, but it’s certainly not been the case for much of the eastern North Island. Many in Hawke’s Bay have told us how green the grass is – not just this year but for the past few years. 

One of the issues we have this summer is the highs aren’t big over NZ. 

An analogy I used recently was to think of New Zealand as a double bed – but the high pressure zones are only for a single bed. This means we have varying wind flows (and weather) around the edges. We’ve seen more rain events in the North Island – although it’s worth noting we do have that “Swiss cheese effect” going on, where within regions there are dry and wet areas. Waikato, Canterbury and Southland are all in this category at the moment.

With February now here the days, I hate to say it, are gradually getting shorter. You mostly notice this in the mornings with the sun rising later each day. This means the mornings are going to become cooler in the weeks ahead – but we’re not done with summer yet. 

Despite the first weekend of February kicking off what can only be described as an “autumnal blast”, the weather is going to warm back up this week with nor’westers out of Australia boosting temps. 

But the high pressure zones will struggle to neatly fit over NZ, and the Southern Ocean is especially stormy at the moment and so more windy westerlies and cold fronts will continue to crash into the South Island.

Meanwhile the tropics is a mess with so much low pressure you’d be forgiven for thinking we’re in the middle of La Niña. The computer modelling has been suggesting that a tropical cyclone will form this week in the Coral Sea. If so, it would be the third named cyclone there so far this summer. 

It thankfully looks as though high pressure around northern NZ will block any chances of this storm reaching us, but Queensland may again be in the firing line. Another cyclone may also form around the Cook Islands.

Rainfall accumulation over seven days starting from 7am Sunday February 4 through to 7am Sunday February 11.

Highlights this week:

• High pressure more dominant over the North Island

• Westerlies off and on for the lower half of NZ

• Another cooler southerly by Thursday

• High pressure arrives this weekend

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