Spring is certainly here and we’re experiencing what I think is a classic September weather pattern, dominated by storms over the Southern Ocean and strong to gale-force westerly winds surging off and on.
The storms south of New Zealand remain enormous – both in size and depth of air pressure. Most lows south of the country have been around the 940 to 950 hPa range now for several weeks. Usually we get a few like that, then that’s it.
You’ve probably seen and heard the words “polar vortex” used a lot this year. The polar vortex is like elastic holding the cold in place around Antarctica – and this year it’s lost that tightness and has more of a wavy shape to it.
Each time the wave goes up from Antarctica it shifts the boundary of cold air and low pressure into the NZ area – and this week that produced a significant winter outbreak over the country with hail, snow and bitterly cold wind chill for newborn livestock.
There is no sign of these storms coming to an end any time soon. The lower air pressure to the south of NZ and Australia isn’t just there only – it exists all the way around coastal Antarctica, with low air pressure storms south of South America and South Africa.
With so much low pressure south of us it means more isobars on the weather maps in our part of the world – and that’s why we’re experiencing the windy westerlies much more this year. They tilt northwest, we get warmer and windier days. They tilt southwest and the Southern Alps get another dusting of snow and Southland and Otago shoulder the colder gloom again for most of the country.
Over the coming week the weather pattern takes a bit of a breather – at least to start with. High pressure looks to briefly cross the country bringing a spell of calm after so many weeks of wind. But it’s short lived, and by later this week the severe gale nor’westers return with the chance of more rain and cold fronts.
While not locked in at the time of writing this, there was evidence in the long-range maps that by next weekend a low will form over NZ as another colder, wintry, southerly comes back in.
There is some good news for those who want a break from the unsettled weather. Long-range data does hint that as October arrives so too does high pressure from Australia. I’m reluctant to lock it in just yet, but GFS modelling out of America suggests New Zealand may well get a calmer period of weather to kick off October thanks to a powerful anticyclone that may be closer to 1040hPa. We shall see. Always good to have a silver lining amongst all this chaos.
Upcoming Highlights from September 23:
• Brief high pressure
• Windy nor’westers and rain
• Possible weekend low
• Possible powerful high-pressure zone moving slowly across NZ next week
