Many people are asking us how come the South Island’s West Coast is in for a drenching this weekend while forecasters say the North Island may not get much at all – despite the front moving that way.

It’s a common set up in summer, many farmers in the western North Island know very well that a rain band on the West Coast (even if associated with rain warnings) rarely fails to deliver in their regions.

So why is this?

Thx for these great updates – out of interest, why do these fronts break apart? What makes them different to those which break the coast and dump rain inland? Always looking to learn! Thanks.

— SB (@sbdairy) December 7, 2017

Well there are actually a number of reasons:

1. The North Island has much higher air pressure this weekend. “A front running into high pressure is like a human-being trying to run in a swimming pool” says head forecaster Philip Duncan. “You may start off strong and full of energy but a lap or so later you soon exhaust yourself and give up”.
2. The Southern Alps shred the rain clouds – and the North Island’s mountains, ranges and Central Plateau do a similar job with higher elevation land also helping break these systems up.
3. Perhaps most importantly the low associated with this front is breaking way from the rain band and dropping away into the Southern Ocean, leaving the rain band squashed between two enormous anticyclones. The centre of a low is the “energy creator” so when the rain band detaches itself quite often the rain band weakens. “It’s basically lost it’s brain centre” says head forecaster Philip Duncan. “It may still move and act like a front but it’s no longer connected to something helping keep it going and eventually it just falls apart and fades out”.

The New Zealand Government owns three commercial forecasters now. WeatherWatch.co.nz, not part of the public sector, remains New Zealand’s only forecaster talking about potential droughts as rain makers continue to fail for those who need it the most – and we continue to react to farmers and growers all over the country who tell us they are very concerned now. 

WeatherWatch.co.nz will definitely keep New Zealanders posted on potential rain makers as we go through this month and across summer – while we understand this is an especially stressful time for some farmers and growers we remain optimistic there is still enough energy around New Zealand to produce rainmakers this summer. Soon we will re-introduce “RainWatch” (a unique service exclusive to WeatherWatch.co.nz) to the NZ news media at zero charge on potential rainmakers – digging much deeper than the basic Government rain icons to help you all even further.

WeatherWatch.co.nz is now also talking weekly to the Ministry for Primary Industries (MPI) and will soon be providing more links and discussions about services to help each other out – please remember you are certainly not alone! We’re all in this together and here to help each other out.

– Image / Sunday afternoon shows the heavy rain in the South Island’s West Coast falling apart as it moves north into higher air pressure and less favourable conditions for keeping the rain clouds active / Weathermap.co.nz

– WeatherWatch.co.nz