Another large area of low pressure is growing over New Zealand and will bring severe weather this week – mainly to the South Island, but there are more localised risks for the North Island too.

The low itself isn’t a “storm” – it’s large and fairly ‘lazy’ and surrounded by two controlling high pressure zones:

• High pressure to the east of NZ is holding this low up and helping to encourage warmer/moisture filled air over the country.
• Another high pressure zone south of NZ is injecting the subantarctic portion of wintry air into this low (and into the South Island, then later the eastern North Island).
• The southern high pressure is also creating a “squash zone” of South-East gales as we go into Tuesday for the lower South Island, as it interacts with the large low centred over the Tasman Sea.

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• Main severe weather risks, generally, look to be from Monday PM to Wednesday PM
• Coldest air is arriving Tuesday/Wednesday in the South Island, then heads northwards later this week in a more weakened state.
• Many other places are warmer than usual further north, thanks to the northerly flow. Some places will be in the mid to upper teens.
• Some are several degrees above normal for this time of year, especially with overnight temperatures.
• By Thursday the entire eastern side of NZ will be colder than average from Southland to East Cape.

The mixture of milder than usual, wet/humid, air from the north will combine with colder air south of NZ moving in – this process can create heavy snow over parts of the South Island (mostly coming into Otago and South Canterbury for the hills and ranges). The low will also bring heavy rain to other areas further up the country.

Snow may be heavy for some farms at higher elevation (above 300 or 400m).

WeatherWatch.co.nz is not currently expecting snow to sea level.

But heavy rain may be more of an issue for those at lower elevation, particularly around coastal/eastern Otago initially.

Rain will also initially be heavy around the north-west corner of the South Island’s ranges where a milder airflow is pushing in rain.

WeatherWatch.co.nz’s main concern for the past week has been for farms/livestock and those travelling (especially roads and flights). With early lambing season already underway in parts of NZ, the wet, windy and cold weather can be deadly. Our latest App and RuralWeather.co.nz both have wind chill graphs, hourly, for 10 days out – for all NZ locations. If it’s raining with windchill near 0 that is a tough set-up for newborn animals.

A number of places in Southland, Otago and Canterbury will have windchill of 0 degrees, or below, in the ‘warmest’ part of the day in the coming week (ie, early afternoon). With rain on top of that this is miserable weather for livestock, especially newborn animals. While lambing peaks in September it starts as early as July.

Strong to severe gale winds are also possible in exposed parts of the lower South Island, making conditions tougher for animals. South to south-east gales will also affect Wellington this week.

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TRAVEL
Flights and highways are also likely to be impacted this week – again especially around the lower half of the South Island and alpine areas, but this could spread into other regions.

Snow at higher elevations is the main concern for highways, while heavy rain and low cloud/poor visibility and maybe even gales at lower elevations are the concerns for airports/flights.

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There are a lot of moving parts to all this – and our Monday video covers this in more detail – but severe weather watches and warnings are now being issued by MetService and are likely to ramp up further across Monday and Tuesday.

Not every region has sever weather risks, some are just wet, mild and cloudy this coming week – the main risk is for the South Island but parts of the North Island will be caught up in this too.

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Get fewer nasty surprises and more local weather data than any other NZ forecaster in the latest FREE WeatherWatch App (incudes paid tier for weather alerts – and official MetService warnings and watches – pushed to devices covering multiple locations – and you set the criteria!).

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❄️#Snow maps. Sleet & snow/rain mix may fall lower elevation than this.

🥶Windchill: For newborn livestock cold rain + wind will make windchill around zero degrees at the warmest part of the day down at sea level, and below zero higher up. Main risk Tonight/Tuesday/Wednesday. pic.twitter.com/vZhSPeW7az

— WeatherWatch.co.nz (@WeatherWatchNZ) July 28, 2024

• WeatherWatch.co.nz
• This Newsfeed page will be updated across Sunday and Monday – so check back.
• A new Newsfeed link will be published on Monday at 5pm covering Tuesday and Wednesday.
• Get fewer nasty surprises and more local weather data than any other NZ forecaster in the latest FREE WeatherWatch App (incudes paid tier for weather alerts (and official MetService warnings and watches) pushed to devices covering multiple locations – and you set the criteria!).