An enormous low pressure system will deepen over the Southern Tasman Sea and New Zealand area this weekend, leading to an Antractic blast in the South Island next week.

WeatherWatch.co.nz says the incoming low is significant and will produce severe weather and is forecast to have very low air pressure, potentially into the 940hPa range which is right up there with some of the world’s largest storms. Deep low pressure storms like this do occur in the Southern Ocean from time to time in winter but this one is forming in the New Zealand area then rapidly deepening in the Southern Ocean on Sunday and Monday altering our weather pattern.

At this stage it looks as though the coldest portion of this weather will arrive next Monday, Tuesday and Wednesday, mostly over the South Island and lower North Island. Despite this storm looking much bigger than what we had this past weekend it will likely be centred much further south of the country and this further south placement means the upper North Island won’t be so vulnerable to the coldest air.

It’s too early to lock in precise severe weather but the most likely risks will be heavy West Coast rain, then bitterly cold southerlies up to gale force in exposed areas and snow levels once again lowering to sea level in the south around Fiordland and maybe Southland and Otago too. Highway closures and flight delays and cancellations are all possible next week in New Zealand.

 TIMELINE:

• WEDS – FRI:  Westerly quarter winds. Increasingly milder than average in the east of both islands. Rain returns to the west.
• WEEKEND:  Saturday kicks off with mild N to NW winds then rain and showers move back into western areas as the low in the southern Tasman Sea now starts to rapidly deepen. A very late S to SE change arrives in Southland and Otago on Sunday PM.
• MONDAY:  Wintry conditions move up the entire South Island with snow to low levels in Southland, Otago and parts of the West Coast. Wintry in the lower half of the North Island but cold and gusty SW winds spread across NZ. Road closures possible. Some flight delays possible.
• TUESDAY:  Another wintry day with snowy conditions and gales in the south of the South Island. Windy and cold in many other regions. Road closures possible. Some flight delays possible.
• WEDNESDAY – Conditions improving slowly but still colder in many parts of both islands.

NOON THIS FRIDAY – Low starts to form and deepen in the Southern Tasman Sea between Tasmania and Fiordland…

SATURDAY – The low starts to rapidly deepen now…

SUNDAY – The low transfers from the Tasman Sea to the Southern Ocean, crossing over the South Island…

MONDAY – The low in the Southern Ocean rapidly deepens (close to a ‘weather bomb’)…air pressure drops to 945hPa

TUESDAY – The storm hugs the South Island before easing towards evening…

– WeatherWatch.co.nz