A second day of violent thunderstorms to rock the North Island

A second day of dramatic and potentially deadly thunderstorms may be in store for the top half of the North Island.

Thundery downpours laced with large hailstones are expected to batter Waikato to Northland throughout the day.

The storms threaten flash flooding, with intense driving rain and falling debris from large hail making it dangerous to drive.

Towering cumulus cloud well to the north of Auckland again this morning ... an early indicator that a few more thunderstorms ⚡ are possible in the upper North Island today. pic.twitter.com/gkmlpeB3m8

— NIWA Weather (@NiwaWeather) November 14, 2017

There is a risk the wave of afternoon storms may be especially severe with huge amounts of hail and the threat of flash flooding as up to 40mm of rain expected to drench regions.

The violent weather forecast for north Auckland suburbs and Northland is expected to bring heavy rain with hail measuring up to 2cm.

The MetService is warning lightning and thunder is likely to strike Auckland, Coromandel Peninsula and Northland this morning. After lunch parts of the Waikato and Waitomo may be hit as well.

According to latest thunderstorm outlook there was a moderate risk of thunderstorms lashing much of Northland, the northern parts of Auckland and eastern Waikato and Waitomo this afternoon and evening.

There is no threat of storms anywhere else in the country.

Yesterday the north was rocked by potentially deadly cloud-to-ground lightning strikes from Whangarei to Waikato.

People were warned to stay inside and keep off the water as more than 600 bolts relentlessly rained down. Parts of Auckland were deluged by hail storms and driving rain that left a set of shops in Takanini awash.

The MetService said a volatile cocktail of cold air at upper levels combining with relatively warm sea surfaces temperatures was behind the unstable conditions turning into thunderstorms.