This week, New Zealand weather kicked off with a southerly off Antarctica. Three days later, the airflow coming into NZ was from out of Australia. There aren’t many parts of the world that get the weather off two continents in such a short time – especially two very different ones (one super cold, the other fairly warm).
Most Kiwis might see this week as more winter weather, but I see it as a sign of spring: the cold blast, the windy weather, then the uptick in temperatures that pushed NZ above average by mid to late this past week.
But to me, the biggest telltale sign that spring’s weather pattern is coming in are the windy westerlies.
We’re now heading into the final week of August. September kicks off next Sunday and so too does the start of spring on the meteorological calendar (with spring not starting until September 23rd on the astronomical calendar). Also, our coldest weather is in June, July and August – leaving September about a degree milder and giving us a bit more spring in our step.
September is also the month that gains a lot of sunlight. About 20 minutes of extra daylight every week, meaning we gain one hour more daylight in September. Then, of course, we get daylight saving towards the end and that gives us another hour of daylight in the evening.
Although daylight saving has absolutely no effect on the weather (obviously!) it is a sign that in just a month’s time we’ll have turned another big corner on winter.
In my view spring this year comes with a higher-than-usual risk of a snowstorm or frost event. This is due to the extra stormy weather over the Southern Ocean and south of NZ lately.
In fact, at time of writing, there is a storm that computer modelling was picking central air pressure to be between 916 and 926hPa for next week. That’s more powerful than most Atlantic hurricanes. Thankfully the storm itself will be near the ice shelf, but the winds will stretch up to Aussie and NZ.
Storms like this that far south tend to produce gale westerlies from Tasmania to New Zealand. Looking at long-range maps that sure seems to be the pattern off and on for the next two weeks. Westerlies streaming into NZ, sometimes with airflows out of Australia, sometimes the subtropics north of NZ, and other times a cold south to south-wester.
The good news is that this set-up should drive in plenty of rain to the West Coast and spill over into our low hydro dams. Several hundred millimetres or more of rain will fall there over the next week or two.
The bad news? Windier, drier westerlies for Canterbury, and a heightened risk of a sudden severe snow or frost event in September. The milder and windier spring westerlies may arrive early this year – but remember: the cold air south of us has only just peaked and hasn’t gone away yet.
