It is not the only adverse weather being felt around the country today.
Canterbury farmers fear expensive centre pivot irrigators might become casualties of gale-force winds.
Gusts of up to 130km/h were felt in the region before inland rain moved northwards.
Federated Farmers Mid Canterbury president David Clark said strong winds have dropped trees, caused power cuts and blown around crops.
In Westland, thunderstorms may continue during the day along with strong wind and even hail.
Heavy rain warnings are in force for the area and the headwaters of the Canterbury lakes and rivers.
Downpours are expected at the headwaters of the Otago lakes and rivers, Buller, the western ranges of Nelson, the Tararua Range and Mount Taranaki.
A southwest change kicking in tomorrow is forecast to push temperatures as low as 10C in parts of the South Island, and bring heavy southwesterly winds to much of western New Zealand.
Those strong and persistent winds are also expected to drive swells up to 7.5m high tomorrow in southwestern areas, with waves potentially reaching up to 10m high.
With tomorrow's big seas forecast to coincide with a low-pressure system and high tides, MetService has issued a heavy swell alert for all of the South Island's West Coast.
A severe weather warning has also been issued, and forecasters are expecting heavy downpours, severe wind and thunderstorms across much of the region.
MetService meteorologist Angus Hines said the swell action is expected to peak at midnight today or early on tomorrow morning.
