From the middle of September to the end of October is when Spring is traditionally at its most chaotic, energetic and changeable.
Both September and October start to see a gradual warming up with a number of days feeling like early summer is coming. These months are also very well known for sudden polar blasts, surprise frosts and the odd comment from people who say “this was worse than any winter weather we had!”. That is ‘peak spring’ in a nutshell.
Take this week. It started several degrees warmer than average. Temperatures then tumbled as much as 10 degrees by day creating for colder than average days for Wednesday and Thursday over a large portion of New Zealand. Now the weekend is upon us and temperatures are again bouncing up above average by several degrees in some areas. In fact eastern regions will even make it into the low 20s this week – ahead of another cool change on Monday and Tuesday.
As we go through October we should see two things – high pressure trying to move in from Aussie for northern NZ and an uptick in westerly winds for many regions further south.
We have cold snaps in the mix with sub-tropical flows too. These mixes of warm and cold air can produce localised dramatic weather (a sudden downpour or thunderstorms, hail or gales suddenly). Spring really is the Jekyll and Hyde season with November usually seeing the mix of highs and lows calming down somewhat and an uptick in higher air pressure and warmer days. We just have to get through the next 5 weeks first – and it looks like more of the same.
– Half a month from now (October 12th) looks remarkably similar to the weather pattern for the end of September.