Whirligig delivers a soaking

20:19, Aug 13 2012

The third winter storm passing over in as many weeks has finally given Christchurch and Banks Peninsula a good old-fashioned drenching.

The last two systems merely flirted with the city and raised the prospect of continuous heavy rain here, which instead took aim further south.

But the low-pressure system that drifted down the South Island on Sunday and looks set to stay in some form or another until late tomorrow has us locked in a sustained head-on collision.

Such subtleties of movement and positioning, and their effect on conditions, are what make weather forecasting - even with all the computer bells and whistles - a difficult business.

August is frequently the stormiest month of the winter in Canterbury. Ironically, it's also the time when, on benign days, we can get lulled into a false sense of security by early-flowering daffodils and camellias that spring has almost arrived.

But if the region is going to get a major winter rain or snowstorm, it will often be during this month.


There's a tad more energy in the air at this time of year than in June or July. The days are now more than an hour longer than they were in late June and early July, and the sun is just that little bit higher in the sky and as such a wee bit stronger. That allows for a greater injection of vigour into the atmosphere, livening up the weather systems accordingly.

It's worth recalling that a year ago this week the entire country was plunged into a polar freeze in the most widespread cold snap for decades. A bitter southerly brought heavy snow to Christchurch and Canterbury, and snow was on the ground from the south of the South Island up through much of the North Island.

This week's storm differs from that of last week, and the one the week before that, in that a small depression centre has formed off Banks Peninsula. This whirligig, which is not moving away quickly, has sat there and has effectively been firing heavy rainbands back at the peninsula and the city.

A persistent bubble of high pressure south of the South Island has been driving the storms on almost the same track across the country.

It would be nice to think this one is the last in the current crop, but there are early signs of yet another possible rain-bearing low this weekend.

The Press