Tuesday, March 5, 2024

December kicks off with some merry chaos

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It’s the high pressure zones north and west of NZ that will make good on El Niño’s ‘hot and dry’ threat, says Phil Duncan.
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December is here and that means the days are still getting longer for a few more weeks yet and summer is only just getting started. 

For the people who heard only “hot and dry” when other outlets talked about El Niño earlier this year, you may soon start to notice more of this pattern. We are expecting to have westerly driven heat this summer at times. But New Zealand’s location on Earth – and it being December – means chaos is a big driving factor. 

Our latest ClimateWatch update was issued last week at RuralWeather.co.nz, covering December, January and February, plus a sneak peek into early autumn. It shows NZ still has “variety” in the weather. 

This means we’re not seeing one big high pressure zone park itself over the country for two months bringing droughts. But we are seeing more high pressure to the north of NZ and to the west of NZ and this generally encourages more westerly winds, which dry out and heat up inland and eastern areas the quickest.

The further north those highs are, the hotter the winds get here. If highs are centred north of the South Island then a nor’wester out of Australia’s interior (hot and dry!) is likely. If the high pressure zone sinks further south over the Tasman Sea and over the Southern Ocean, we get colder airflows. 

So those high pressure zones north and west of NZ are critical for us to get that “hot and dry” component with El Niño. 

Over November the main guiding high pressure zone dropped so far south from Tasmania it opened a giant vacuum over New South Wales and Queensland for weeks of heavy rain and thunderstorms. 

Some places have had hundreds of millimetres of rain that, only six weeks ago, had widespread bush fires. That extreme southern placement of high pressure helped Australia out of an early drought – and has also given NZ a messed-up, wetter pattern for November and early December.

Which brings me to Hawke’s Bay. I feel for those of you in the north and into Gisborne region with yet more floods and slips. If anyone in NZ is angry at forecasters or wants to say “So much for El Niño,” it’s those living there. I’ll take the criticism too, although I’ll push back that we weren’t the forecaster that was heavily promoting “hot and dry” across the mainstream news outlets a few months ago. 

But we did expect eastern areas to be drier by now, and while that’s something most farmers heading into an El Niño summer would never wish for, I do very much appreciate why this particular part of NZ is so fed-up with the forecasts and the weather itself. 

The chaos that led us to this messy pattern is still around – and so December may still get some rain into those sodden eastern parts of the North Island. But long term, we do see a drier phase emerging in the east over the next two months ahead.

El Niño Watch | Why farmers should heed long range El Niño advice

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