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More bad weather to come for NZ

SATURDAY JULY 14, 2012

The next polar blast is due to pop by in the final days of July, when the moon reaches its southernmost point for the month whilst in perigee.

And that won't be the last. In the first week of August a cold taste of winter travels up country courtesy of a large anticyclone beneath Tasmania. This polar blast could bring us icy temperatures, especially around 5th and 6th.

The fourth week of August may bring downpours to central, west and south districts of both islands, followed by a fortnight of cold southerlies with snow and ice that may cause disruptions on a number of Southland and Otago highways including Arthurs, Lewis, Porters and Lindis Passes and Nelson’s Takaka Hill, and possibly closing the North Island's Desert Road.

September too has its fair share of the nasty stuff, beginning with a dominating cocktail of cold and warm fronts that generate wintry weather, due to a low pressure system sitting west of the South Island. 

Then, in September's third week, squally fronts may cross the country bringing downpours to central North Island districts and snow to low levels in the south of the South Island and east coasts.

As a result roads may be closed south of the South Island and perhaps again the Desert Road.  Widespread snowfalls may affect new born lambs in the far south.  And in September’s last week, as low pressure again dominates, cold fronts could carry further snow and ice over the far south and Otago..

October, too, is a month with a bad attitude. For the first ten days lower pressures may rule the roost with snowfalls over the east of the South Island.

In the last week of October a temperature drop brings more cold southerlies and wintry precipitation affecting the north and west of the South Island, and the centre and east of the North Island.

Altogether about 15 further cold southerly systems are expected over NZ between now and the end of October.

Polar blasts in August may be on or near the 1st, 4th-10th, 17th, 20th-24th and 30th-31st; in September around 3rd-4th, 10th-12th, 15th-16th, 18th-19th, 28th-30th; and in October about 8th-10th, 12th, 15th-16th, and 22nd-26th. August brings the chance of snow about 1st-2nd, 4th-5th, 9th, 18th-19th, 20th and 27th.  Snow in September may be in the second third and fourth weeks, and in October around 1st-2nd, 9th, and 24th.

Overall the South Island may get most snow days because the expected shallow anticyclones in the North may keep low-pressure precipitation-laden systems arriving from under the Australian Bight south of Cook Strait.

August could be the year's wettest month for the North Island, with October the second wettest. For both islands October may be very much cooler than the norm.

So there is probably still a lot of winter left to come. Do not be sucked in by the positive reactions when early buds become visible. Often when expressions of delight and relief rush to fill the news-hungry media many are misled into thinking the brunt of winter is over and are caught unprepared and surprised when further polar blasts arrive unannounced. Forecasters will then blame the climate for being fickle and bizarre, creating more news stories.

Even November has its share of unsettled weather with potential for storms and floods in the second half, and this year it would be unwise for those who earn a living outdoors to become complacent until December.

There is a more detailed description of NZ weather to come during the winter months, in our July/August newsletter. To sign up for the newsletter, click http://www.predictweather.co.nz/Register.aspx .

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