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September Outlook: Windy westerlies, big highs and big lows, welcome to chaotic spring!

We’re entering true spring weather as we head into September and that means more chaos and changeable conditions. Spring weather is all about hints of summer coming in and winter weather slowly fading away.

The new month is actually kicking off settled with high pressure. Next week New Zealanders will enjoy warmer than average conditions by day in many regions. But by the end of Tuesday a sub-tropical rain maker will be descending on northern NZ. This low clears away on Wednesday then by Thursday back come the windy westerlies.

Next Friday and Saturday may be a bit more wintry and unsettled again with a low tracking by creating a burst of rain, mainly up the western side of the country, then colder S to SW winds for a time. We may get another dusting of snow on the Southern Alps next weekend or the very start of next week as things turn colder for a time.

As we head into the second week of September high pressure may be north of NZ and low pressure around the South Island – making for unsettled weather the further south you go to start the week, but the week may see that high pressure growing around the country, or it may continue the windy westerlies.

Long range models indicate a fairly unsettled month ahead with large highs out of Australia coming our way calming things at times but also encouraging windier westerlies, made windier with a few low pressure systems in the mix too,  around the Tasman Sea but mainly south of NZ in the stormy Southern Ocean.

There are currently no direct polar blasts in the forecast but being spring we’ll keep a close on the Southern Ocean as September is a critical month for farmers and growers. One of the tell-tale signs of potential for a big polar southerly is often a large high over Tasmania that stretches from north to south (rather than the usual sideways west to east). It’s this tall north/south shape that best scoops up colder air near Antarctica then dredges it back up over NZ. If you’re looking at various long range models those are the types of set ups WeatherWatch pays close attention to each and every winter and spring for potential polar weather. 

MAP – Air Pressure map for next weekend (ECMWF)



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