MetService has issued a severe weather watch as a subtropical low is expected to bring heavy rain and possible severe gale northeasterlies to parts of the upper North Island and the Tasman District.

"A subtropical low over the Tasman Sea is expected to direct a strong and moist northeast flow over central and northern New Zealand on Wednesday and Thursday, with some areas likely to receive warning amounts of rain and possible severe gale northeasterlies," says a MetService spokesperson.

"Also note that large northeast swells could bring hazardous conditions to exposed coasts."

Heavy rain could cause slips, surface flooding and damage to roads.

Severe gales could make driving conditions hazardous, especially for motorcycles and high sided vehicles. Temporary structures such as tents could be affected.

People are advised to keep up to date with the latest forecasts from MetService in case any changes are made, or further areas are added.

A Heavy Rain Watch has been issued for the following areas:
Area: Auckland including Great Barrier Island
Valid: 24 hours from 9:00am Wed 4 Jan to 9:00am Thu 5 Jan
Forecast: Periods of heavy rain. Rainfall amounts may approach warning criteria, especially in the north and east.

Area: Coromandel Peninsula
Valid: 24 hours from 9:00pm Wed 4 Jan to 9:00pm Thu 5 Jan
Forecast: Periods of heavy rain. Rainfall amounts may reach warning criteria, especially about the ranges.

Area: Bay of Plenty west of Matata
Valid: 27 hours from 3:00am Thu 5 Jan to 6:00am Fri 6 Jan
Forecast: Periods of heavy rain. Rainfall amounts may reach warning criteria.

Area: Tasman west of Motueka
Valid: 24 hours from 12:00am Thu 5 Jan to 12:00am Fri 6 Jan
Forecast: Periods of heavy rain. Rainfall amounts may reach warning criteria, especially about the ranges.

A Strong Wind Watch has been issued for the following areas:

Area: Northland
Valid: 30 hours from 1:00am Wed 4 Jan to 7:00am Thu 5 Jan
Forecast: Northeast winds may approach severe gale in exposed places.

Area: Auckland including Great Barrier Island
Valid: 24 hours from 9:00am Wed 4 Jan to 9:00am Thu 5 Jan
Forecast: Northeast winds may approach severe gale in exposed places.

Area: Waikato, Waitomo, Taumarunui, Coromandel Peninsula, Bay of Plenty about and west of Tauranga, Taupo, Taranaki, Taihape
Valid: 24 hours from 6:00pm Wed 4 Jan to 6:00pm Thu 5 Jan
Forecast: Northeast winds may approach severe gale in exposed places.