A very large low pressure system will form this Friday and Saturday and then take a few days to cross New Zealand.

As it does so it will dredge up cold Southern Ocean air over the South Island and right up along the eastern side of Australia. Heavy rain with sub-tropical connections will be funnelled into Canterbury with early estimates suggesting as much as 200mm might fall in some parts of Canterbury.

This is a significant amount and may well lead to slips and flooding. We’ll fine tune the risks zones further in our Friday video update.

Heavy snow is also on the way for the Southern Alps.