Showers have already begun in what is expected to be two days of heavy rain and possible thunderstorms for the top half of the North Island.   

MetService has forecast up to 22 hours of rain as tropically-fuelled disturbance sparks unsettled weather before the weekend. 

MetService meteorologist Kathryn Hodge said patchy rain has already started in Northland and is expected to spread down the North Island later in the day. 

“It will reach Auckland in the afternoon. But there is a risk of thunderstorms in the afternoon for Northland and for Auckland late at night,” Hodge said. 

A heavy rain watch is forecast to come into effect for Northland from 1pm and last for 22 hours through to tomorrow morning. 

MetService says there is a moderate chance of it being upgraded to a warning. 

Heavy rain watches are also coming into force for Auckland including Great Barrier Island and Coromandel Peninsula from 8pm lasting 20 hours until 4pm tomorrow, and for Bay of Plenty and Rotorua from 10pm until 8pm tomorrow and Taranaki from 10pm until 6pm tomorrow. 

There is currently a moderate chance these would be upgraded to warnings. 

Hodge said the front bringing the wet weather was spreading down the country. 

“While there is a little bit of patchy rain ahead, with the front [the rain] will pick up.” 

Niwa said: “Two disturbances in the Tasman Sea will drag tropical moisture into New Zealand from Friday into next week. 

“The combined system will produce rounds of heavy rainfall, particularly in the northern and eastern South Island, possibly swirling in the Tasman for up to a week.” 

MetService meteorologist John Law said the heavy rain and possible thunderstorms would also likely bring windy conditions, “especially overnight, Thursday into Friday, into the northern areas,” Law said. 

For the South Island, a heavy rain watch is set to come into force for Tasman from 6pm and last 24 hours. 

There is a moderate chance this would be upgraded to a warning.