The heavy downpour that has battered the top of Northland is expected to move slowly down the country today, bringing rain and possibly thundery showers to Auckland.

Meteorologist Douglas Mason said an easterly flow had caused high rainfall along the coast, with some parts of the sodden north getting between 80mm and 100mm of rain in the past 24 hours.

"There is the odd thunderstorm mainly offshore but that thunderstorm risk will persist through the morning and lessen through the afternoon in some parts of Northland," Mason said.

"Currently we have a rainfall watch out for Auckland, Great Barrier Island and Coromandel Peninsula and that is valid until 6pm."

Rain in Auckland would approach warning criteria - 50mm in six hours or 100mm in 24 hours - but was not expected to "quite get there".

"For most of the country, it is extensive cloud."

Rain is expected to continue tomorrow in Auckland.

Gale force winds are battering the North Island this morning in the Brett, Kaipara, Colville, Raglan, Bay of Plenty and Stephens areas.

A severe thunderstorm watch was issued by MetService yesterday for Northland due to a frontal rainband in the north Tasman Sea.

The low was expected to move slowly southeastwards during Tuesday and Wednesday, bringing a strong, cold south to southwesterly flow to the South Island.

During Wednesday and early Thursday, heavy rain was likely about Marlborough and Canterbury, north of about Timaru, with heavy snow likely above 400 metres.

Today's forecast
Auckland: Rain, with heavy falls and possible thunderstorms, easing evening. Northeast, gale in exposed places this morning. 18C 13C
Hamilton:Periods of rain and gusty easterlies. 15C 11C
Tauranga: Periods of rain, with heavy falls. Strong northeasterlies. 17C 12C
Wellington: Mostly cloudy. Occasional light rain this evening. Southeasterlies. 14C 10C
Christchurch: Mostly cloudy with drizzle. Northeasterlies developing afternoon. 11C 7C
Dunedin: Long fine spells. Northeast breezes. 11C 6C
Source: MetService