A series of low pressure centres filing past Stewart Island will bring an unsettled westerly weather pattern to the country this week, with the first low pressure system moving past on Sunday afternoon.

As well as strong to gale westerlies, each low centre will direct a brief southerly change up New Zealand, and bring rain, snow and thunderstorms to parts of the country.

The entire South Island, as well as the lower North Island, is currently under a Severe Weather Warning or Watch for west to northwest gales today.

Current forecasts suggest that the Canterbury High Country and foothills, as well as Marlborough, Wellington and the Wairarapa, will be the windiest places, and each of these places may see wind gusts of 140km/hr.

Western parts of the South Island will see a double dose of severe weather, with Warnings out for heavy rain and high risks for thunderstorms in Fiordland, Westland and about the Southern Alps, as the frontal system progresses northwards this afternoon.

Behind today's front, the wind direction shifts to the southwest, and deep, cold air pushes across the South Island, bringing snow to low levels. Current forecasts are for the snow to lower to 600m in the far south Sunday evening, then further lower to 300m for a time early on Monday for Fiordland, Southland and parts of Otago.

'Strong wind will certainly be the most noticeable weather for many people this week,” says MetService meteorologist Angus Hines, 'but with the upcoming cold southerly changes, and a procession of fronts providing moisture, is also looks likely that snow levels will lower even further as the week goes on.

'There are already many Road Snow Warnings in place for higher South Island passes, and it looks inevitable that more roads will be affected and more warnings issued. It's safe to say that winter is coming.”