There are some mighty dramatic news headlines in New Zealand this week about the incoming low pressure system from the sub-tropics, so we thought we’d do our best at clarifying a few points.

Firstly, it is not a storm moving in. It’s a large low – but large doesn’t mean aggressive when it comes to low pressure, nor does it always mean the low is deep/intense. The bulk of the wind is being generated by the developing low pushing against high pressure systems and creating windy ‘squash zones’. A true storm has gales wrapped all the way around it.

However by Friday this low will be deepening further into the 990hPa range and that means areas of heavy rain and some gales are possible – but generally speaking this is a big low with pockets of strong winds, heavy rain plus decent amounts of calmer and drier weather. 

TRACKING THE HEAVIEST RAIN:
There are two rain bands. One tracking up the South Island overnight and into Thursday while the main one tracks southwards over the North Island tonight and Thursday.

The heaviest burst of rain in the North Island comes in tonight and overnight and then heads south over the North Island gradually across Thursday. In other words, most get rain but whether it lingers all day is another question. Some may have rain easing early to drizzle or showers, others easing to dry spells while some in the east especially may have a day of rain. 

On Thursday the rain in the South Island ranges will turn to snow and showers develop in the upper North Island, possibly with thunder around Northland later.

By Friday the bulk of the rain will lie over the eastern and upper South Island and perhaps some eastern parts of the North Island with plenty of dry spells forming elsewhere.

The worst of the rain heads out to the east on Saturday, but may linger longer in the North Island’s east coast.

 

TRACKING THE STRONGEST WINDS:
With the low still deepening we expect windy weather to become more widespread over the coming days – but the large size of the low means the energy is stretched out further (unlike a cyclone where the energy is crammed near the centre creating those destructive winds).

Nor’easters will be blustery, mainly later today in the upper North Island (north of Waikato) between the centre of this low and the high we’ve had over New Zealand these past few days – this is called the “squash zone”. This then tracks southwards overnight.

During Thursday these blustery winds and possible gales mostly are confined to Central NZ and the Cook Strait areas and some coastal places. It’s not too bad otherwise for most people but the winds through this central area may funnel through and increase further.

Friday sees a lot of calm weather in the North Island as the large centre of the low comes in – but the back end of the low arrives in the upper and western North Island later in the day and so strong SW winds will likely kick in then.  Cook Strait and central NZ also looks fairly windy on Friday from the south east.  

Overnight Friday and into Saturday that windy SW flow will increase further in Auckland and then may spread to many other places across the day.

TO RECAP
Most places will get wind or rain at some point, especially the North Island and the South Island north of Canterbury. However severe weather may be far more isolated. Most main centres look like they will avoid severe weather at this stage.

It’s one of those systems that we say is “one to watch” – just in case it intensifies further than the reliable models and forecasters have picked, but at this stage it’s hopefully not going to be too nasty – but certainly a bit a messy end to the week and a windy start to the weekend.

*Please keep up to date with any weather warnings issued by MetService as well – as of 11am a few had already been issued.

**Look out for next weather video – it will be available this afternoon.

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– Noon Friday shows heavy rain around Canterbury with gusty cool SE winds but perhaps things drying up and calming down for many in the North Island as the centre of the low comes in / Weathermap

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