After three months of high pressure dominating many parts of NZ a new Autumn weather pattern is finally emerging, but it’s a slow change.

Autumn is slowly arriving this year – some years it can rush in fast, so why is that? Some may over complicate it but to be honest it’s simply the fact we’re two small mountainous islands partially caught up in the very changeable roaring forties weather. So a few months of high pressure can put us in drought – and a few big lows can totally reverse this. It’s something that our meteorologist partners at CNN Weather have noted many times – how single air pressure systems can dwarf our country and we can buck trends sometimes due to this. This also can make seasonal forecasts redundant sometimes due to our small size.

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The trend this year has been one high after another bringing warmer than average and drier than average conditions. While the Tasman Sea is warmer than average (and that leads to more rainmakers) there have been few rainmakers for NZ itself because high pressure has protected us/stopped that from happening. Once the highs break this will allow the warmer sea waters to help fuel heavier rain events, something WeatherWatch.co.nz exclusively told journalists earlier this year when Government forecasters were talking about big rain events for February which never arrived, because of the high pressure stopping them.

When we take a look at how the weather systems line up in the second week of April we notice something new – the highs are no longer all perfectly linked up. Now we have lows in between each one. These means two things. 1) We have about a weekly chance of rain now, including for our driest regions – even if totals aren’t high it is a start to reverse the big dry that has formed. 2) We still have a lot of dry, sunny, days too thanks to these highs so this bodes well for pasture growth.

So to recap, we have a better chance of rain for NZ’s driest regions – but if you love the summer weather it’s not rushing away fast either. April looks to be an extension of summer weather for many, especially in the upper North Island.

MSLP (air pressure) map for April 7th shows lows developing between the highs, making for more variety in our weather pattern…

– By WeatherWatch.co.nz head forecaster Philip Duncan.