A large low that has stalled in the Tasman Sea and brought rough weather to Sydney is now about to bring rain and some wind to New Zealand – but it’s not clear cut and not what you might think.

We are not in for several days of nonstop rain – instead we have a slow moving set up where a large high will dominate New Zealand and affect which regions get rain and which do not.

It’s a bit like having a traffic cop in the sky, redirecting the natural flow of traffic. 

This high will move east of the country this weekend allowing the low in the Tasman Sea to not only move closer, but to actually cross the Cook Strait area overnight Sunday and into Monday morning, ensuring most of New Zealand will have rain, showers or winds at some point.

In the meantime, that high will push a lot of wet weather away from New Zealand too.

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So what is exactly happening each day with the rain?

Tuesday – South meets north as a southerly heads into the North and directly into the northerly flow that is developing there.  Rain is developing across New Zealand today, mostly Canterbury northwards. Heaviest falls will be in the North Island overnight tonight and into Wednesday AM. Great to see rain in drought affected Canterbury today too.

Wednesday – High pressure starts to cover all of the South Island and the lower North Island – ie, nothing to see here! Meanwhile heavy rain will ease in Hawke’s Bay in the morning as the high builds further south. It’s hard to exactly track the rain bands for the rest of the Upper North Island as the airflow switches from northerly to south easterly during the day and that may then send some rain clouds back where they come from – but our hills and ranges (ie, Coromandel Pen, Kaimai’s etc) will shelter others while making heavier falls for some. Generally speaking patchy morning rain for the upper North Island with dry spells increasing as the day goes on for most regions. Wednesday should end mainly dry for most regions.

Thursday – Remember that high over the South Island? Well it balloons out on Thursday over more of the North Island. This then pushes that rain back north of New Zealand out to sea for the most part.  Other forecasters and TV weather may be heavily applying rain symbols but in reality the easterly flow may only bring in a few showers to Northland, Coromandel and East Cape. We expect Thursday to be mainly dry for New Zealand. Patchy rain or more frequent showers may move back into Northland, Coromandel, BOP and parts of Auckland on Thursday night – but drizzle or dry spells in the mix too.

Friday – The low in the Tasman moves closer and the high over the South Island squeezes eastwards. This turns the easterly flow over the upper North Island into a nor’east flow and this will send another rain band southwards from Northland across the day. This rain will slide into Auckland, Coromandel Peninsula and western BOP as the day wears on.

Saturday – That band of rain continues to track across the North Island bringing heavy rain to BOP. Then very humid northerlies cover the North Island with showers and isolated heavy downpours.  The sun may even come out and if so that will enhance the chances of thunderstorms popping up here and there in the sub-tropical airflow. Plenty of dry spells on Saturday, including in places like Auckland and Hamilton.

Sunday – The day that the low finally moves in. Periods of rain or showers, focusing more around central NZ as the day goes on. Heavy rain could move into Nelson and rain may again fall in drought hit Canterbury. Dry spells develop in northern areas too. Westerlies return in the north.

Monday – The centre of the low crosses New Zealand roughly right in the middle of the nation. Most regions will have wind, rain or showers for a time on either Saturday, Sunday or Monday.

Tuesday – High pressure returns.

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How much rain and will there be flooding?

Rainfall totals will really vary within each region let alone region to region. Grand totals we’ve seen over the coming  days in the wettest areas of the upper North Island goes from 50mm to over 100mm – this is spread over seven full days with plenty of dry spells in between – in other words, it won’t rain non-stop for several days but some wet weather is possible in some areas every day. Flooding will only be an issue if the rain bands stall anywhere, or if afternoon heating creates torrential downpours on Saturday, otherwise it should be spread out over a few days lessening the chances of serious issues. 

Don’t forget to check MetService who are funded by the taxpayers through the Government to issue weather watches, warnings and outlooks for every single part of New Zealand – land and sea.

The rain forecasts are complicated this time around – At WeatherWatch.co.nz we’ll do our best to go that extra mile to make sense of it all for you and how it might impact you, but due to the size and nature of this low we do expect some more “fine tuning” to be done over the coming hours and days.

– WeatherWatch.co.nz