Niwa recorded around 5000 lightning strikes offshore and near the western South Island yesterday, while MetService recorded 1408 over a two-hour period with plenty more to come over the next couple of days.
An unstable west to northwest flow would cover central and southern New Zealand during the second half of today bringing thunderstorms to many western and southern areas.
In Taranaki and coastal Waitomo, any thunderstorms that develop would bring heavy rain and big winds that could exceed 110km/h and become damaging.
A heavy rain watch is in place for Taranaki, Taumarunui and Taihape until 6pm tonight.
Western North Island areas from Kawhia to Wellington, as well as Marlborough Sounds, could also see thunderstorms accompanied by heavy rain, hail and big winds.
MetService has warned northwest gales could reach 130km/h in Wellington and could damage trees, powerlines and unsecured structures while making driving hazardous, especially for high-sided vehicles and motorbikes.
There is also a risk of thunderstorms in western South Island areas from Farewell Spit to Milford Sound, coastal Southland and Stewart Island, bringing heavy rain, hail and snow to 500-600m in the south and 900m in the north.
Thunderstorms could also hit inland Southland, eastern Otago and South Canterbury this afternoon and evening bringing hail and snow to 700-800m.
Weather warnings have been issued for large areas of the South Island - including rain warnings for Buller, Nelson, Westland north of Otira, and Fiordland.
In the North Island, those in the Bay of Islands could see periods of heavy rain with a warning in place until Wednesday 3am.
On Monday, Otago recorded the strongest wind gusts in the country, according to Metservice.
