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Column: Sub-tropical low now deepening

By head weather analyst Philip Duncan — The most significant low pressure system for New Zealand so far this year is about to arrive with both wind and rain – but is it really a “game changer”? first talked about this potential low back in March based on long range models.  It was then that we told the Ministry for Primary Industries (the authority that declares official droughts) that we have a “significant” low pressure system for mid-April.  The million(or maybe billion) dollar question back then was “Would the rain fall over New Zealand, or over the sea”.  The good news is, all the models seem to indicate this low will bring substantial amounts of rain to many parts of New Zealand, especially the North Island.

Some modelling I’ve looked at actually indicates the bulk of the rain will fall over the North Island and upper South island and not out at sea.

We believe north facing and north west facing places (like Nelson and BOP for example) are likely to see the heaviest rain, with eastern areas (like Wairarapa, Hawkes Bay) potentially receiving less.  I say ‘potentially’ because this low will be changing shape and structure as it crosses over the country around Tuesday.

Because of our large mountain ranges a slight change in wind flow can have significant consequences to where the rain falls.  A slight shift may see significant relief turn into significant frustration.  It’s for this simple reason that we aren’t saying “all the droughts will be fixed by this low” – but we believe many farmers are going to be happy with the rain that falls.

The low is the first one this year to really bring energy – in the form of heavy rain and strong winds – to our more populated regions of the North Island.

Today it continues to deepen and will deepen right up to, and during, it’s time over us – the lower the air pressure goes the more energy this low has.

The stream of highs that were 100% responsible for the droughts this year appear to now be losing their monopoly and the rain makers are biting at their heels.  Well, early next week, this low will do more than just bite at the heels – it will chomp a great hole out of the high and allow more rain makers and lows to return to New Zealand in the following days after.  It’s all looking a lot more positive than it did a month ago that’s for sure.

@PhilipDuncan on Twitter



Shane on 13/04/2013 2:24am

Hi there

I was just wondering if this low has the potential to contain thunderstorms?


WW Forecast Team on 13/04/2013 2:47am


We have it as a low risk but not counting it out completely. Might be possible later next week with the next system.



sw on 12/04/2013 8:11pm

Its obvious sometime in April there would be some sort of a depression in april,its 30 days of possibilities.

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