A ridge of high pressure covering New Zealand on Tuesday morning is expected to weaken, according to MetService forecasters.

"A convective rain-band in the Tasman Sea will move onto northern and central parts of the country during the second half of the day with possible thunderstorms and/or short-duration downpours," a Metservice meteorologist said.

"There is low confidence that a heavy rain warning may be required for Northland from afternoon, and other parts of the northern North Island from western Bay of Plenty and Taranaki northwards from evening."

On Wednesday, a convective rain-band will be moving across central New Zealand on with possible thunderstorms and/or short duration downpours.

"A showery northwest flow follows the rain-band over the North Island, and an easterly flow develops over the southern South Island."

MetService said the rain-band may bring some brief heavy falls and thunderstorms to the central North Island during the early morning on Wednesday, and there is low confidence that a heavy rain warning will be required.

A showery northwest flow should cover the North Island on Thursday, while easterlies and rain affect much of the South Island.

"There is low confidence that northwesterly rainfall amounts could reach warning criteria about western Waikato, Waitomo and Taranaki, and that east or northeasterly rainfall could reach warning criteria about South Canterbury, North Otago and northern Dunedin."

On Friday a large shallow low is likely to cover the South Island, while a westerly flow is expected to cover the North Island.

"At this stage, there is minimal risk of severe weather affecting the country."