New Zealand’s in pretty good condition as we round the corner to spring weather conditions. Whether you go with September 1 or September 23rd as your official start to spring, it’s clear August is still winter technically – but NZ’s location on Earth means we can experience spring weather conditions this month (just ask someone who suffers from allergies thanks to pine pollen, which can often start in August).
The last week of July encapsulated what we said in our May update of ClimateWatch (our monthly outlooks). We expected a series of large highs and large lows to come through this winter, bringing real variety in weather, and in the final week of July we had a low pressure zone in the Tasman Sea which had a sub-Antarctic feed coming into the South Island and a subtropical feed coming into the North Island. No wonder New Zealanders can’t agree on if this winter has been much colder than usual or much warmer!
The larger an air pressure system is, the more “reach” it has – by that I mean it can scoop up air from Antarctica and dredge it into NZ, or drag down tropical air over us. Big lows are often seen as “stormier” but in reality they can be “lazy” and just hang around for a long time.
And “big” is the theme of this winter – because July not only had a high pressure zone so powerful it broke air pressure records in NZ that were 135 years old, but we’ve also had a number of very large low pressure zones that have brought heavy snow into both Australia and NZ, and warmer than usual rainfall for northern NZ.
So, back to August. There’s no shortage of big high pressure zones and this month has kicked off with a high moving in – the very same anticyclone that, a week ago, dredged up the snow and frosty South Island change and made Sunday and Monday (August 5) colder in the North island.
It is actually splitting in half. The second half of this high (the main part of it) crosses NZ this week bringing changeable west to southwest winds over the lower half of NZ – but still plenty of settled weather too.
At the time of writing this column, the seven-day outlook for NZ was drier than average for most regions, with the exception of Northland and Fiordland – a sign that the incoming high is going to be elbowing away most rainmakers as we go into this new month.
The GFS model out of the United States picks this high pressure zone to linger over NZ until the middle of August, meaning colder nights but milder and much drier days. While we can’t lock in a forecast for two weeks away, the modelling I’m seeing right now shows this anticyclone finally departing NZ mid-month with a sub-tropical airflow coming in, then a low from the Tasman Sea.
We’ll see if that pans out or not, but either way, the winter of “big and slow” high and low air pressure zones continues.
