Heavy rain and marble-sized hail could hit Auckland and Northland this afternoon as a severe thunderstorm watch comes into effect. 

The two regions are under the watch from 1-9pm today as a stationary front, currently sitting over the upper North Island, becomes unstable. 

MetService meteorologist Michael Pawley told the Herald the instability will bring heavy showers and a risk of severe thunderstorms. 

For inland and western Northland, and Auckland about the Kaipara Harbour, there is a moderate (30-60%) risk of severe thunderstorms bringing 24 to 40mm/h downpours in isolated areas. 

There is a high risk (greater than 60%) of regular thunderstorms for those areas this afternoon and evening. 

MetService has warned such severe storms can produce marble-sized hail and rain which can cause surface or flash flooding, especially in low-lying areas. 

For the remainder of Northland and Auckland, there is a moderate risk of thunderstorms in the afternoon and evening. 

“The nature of this type of shower activity, and it’s a big area that can be affected, but they pop up in very localized places”, said Pawley. 

Despite the downpours, high temperatures of 25C today and 24C tomorrow are forecast for Auckland. 

The bad weather is expected to hang around tomorrow with thunderstorms possible across the upper North Island. 

Tomorrow afternoon, there is a moderate risk of thunderstorms with heavy rain affecting Gisborne, Bay of Plenty, north Taupō, eastern and northern Waikato, Coromandel Peninsula, Auckland and Northland. 

For inland Northland, the far east of Waikato, Rotorua and inland Bay of Plenty west of about Kawerau, there is a 10-30% risk of severe thunderstorms with localised downpours of 25 to 40mm/h, according to MetService. 

Despite bad weather in the north, a sunny Saturday is in store for most of the country today. 

MetService said the middle part of the country will have high temperatures and sunny weather, with Gisborne predicted to peak at 28C. 

In Hawke’s Bay, temperatures above 25C are forecast around the region with some places reaching 30C early next week. 

On Monday, the western South Island is forecast to get heavy rain with a heavy rain watch in place from 9pm on Sunday to noon the following day. 

The same watch is in place for the ranges of the Westland District from 3am-3pm on Monday.