Low pressure is swirling around central NZ and as it moves eastwards the main Antarctic southerly being sucked up behind it spreads further north. Temperatures have already dropped nationwide but some North Islanders may be surprised to know the main cold air hasn’t come in yet – instead it’s still building in the Tasman Sea.

As the low continues to move away from NZ it will allow this polar southerly to be pulled up and in behind it and spread right across the North Island. 

Late morning Saturday heavy rain flooded many streets and intersections in Christchurch as the centre of the low tracked by. That rain band has eased there now but is moving into Wellington with the developing southerly change.

This southerly will spread up the North Island tonight and overnight as the somewhat milder westerlies move away and out over the Pacific Ocean, allowing the cold Southern Ocean/Tasman Sea southerly behind it to move in.

The satellite imagery in the animation below shows water vapour. The colder the air is the less moisture it can retain so that’s why you can see a dark channel of drier weather at the centre of the Antarctic southerly blasting into the Tasman Sea area. The bright white around Canterbury and Wellington is the heavy rain cloud attached to the very centre of the low.

Think of the #AntarcticBlast an extra big cold wave that goes up the beach & juuust goes over the normal high tide mark. That’s how this #SoutherlySurge is behaving, peaking north of #NewZealand before sliding back south on Monday PM.

Maps: Noon Saturday, 3am Monday, 9pm Monday pic.twitter.com/HH7l7vlSJM

— WeatherWatch.co.nz (@WeatherWatchNZ) June 1, 2019

– WeatherWatch.co.nz