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(Maps) Rain warnings on the way again?


With so much heavy rain lately even a relatively short lived downpour could create serious surface flooding – and the possibility of sustained heavy rain could be even more damaging.

The Queens Birthday Weekend low that’s being forecast for northern New Zealand still has a significant amount of uncertainty around it.

As with all lows that come from north of New Zealand it’s much harder to know if they will have a direct hit on us – mainly because the shape of northern NZ means it’s more like shooting a basketball into a hoop than kicking a rugby ball between the posts.

So what are the current predictions? 

 (of as Wednesday evening)


“During Friday and Saturday, a large anticyclone should move eastwards over New Zealand.

On Sunday, a large area of low pressure should start to move onto the North Island. Its associated frontal band should bring rain to most parts of the North Island, and there is a low risk that amounts will reach warning criteria about Northland, the north and east of Auckland, also Coromandel Peninsula, Bay of Plenty and northern Gisborne.

There is a lot of uncertainty over what happens on Monday. It is possible that a frontal band becomes slow moving over the South Island embedded in a strong easterly flow. There is thus a possibility of heavy rain about Wairarapa, Wellington, Marlborough, Canterbury and Otago. However, confidence is only low at this stage” – MetService.

GFS (as of Thursday morning)

Sunday night over New Zealand shows a deep low over Northland…yesterday it was well off the north eastern coastline.  This is what we call a computer model “wobble”…and you can see why it makes long term predictions hard.


This computer model for Sunday night shows the low directly hitting New Zealand…with a heavy band of rain possibly hugging the east coast of the North Island (and maybe the north eastern coast of the South Island on Monday).
Our current data says there’s now a 60% likelihood of rain over Northland, Auckland, Coromandel and East Cape on Sunday or Monday morning – but percentages drop significantly for other regions.

With so much uncertainty it’s definitely one to watch closely.  By Thursday evening or on Friday we will most likely know which model is the most accurate….unforunately, it’s becoming clearer that this low IS going to have an impact on our weather this weekend.


Ken Ring on 2/06/2010 7:40pm

The moon crosses the equator heading north on Saturday. Whenever this occurs (lunar equinox), weather systems speed up and it is traditionally the time in the month when the models get the timing least correct, because weather changes more quickly, and the models assume a constant speed. Hence I would suggest the unsettled weather may be arriving earlier.

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