Weather warning: Heavy rain forecast in South Island today

A severe weather warning is in force for parts of the South Island today, where heavy rain is expected.

The MetService has issued heavy rain warnings for Westland, south of Otira, and the headwaters of the Canterbury lakes and rivers, south of Arthurs Pass.

"An active cold front is expected to cross the South Island late Wednesday and early Thursday, bringing a period of heavy rain to the west of the South Island.

"The heaviest rain is forecast about the ranges of Westland from this evening until early [tomorrow] morning, with 100 to 150mm likely.''

The rain over the Westland area is forecast to ease by early tomorrow morning.

In the Canterbury region, the heavy rain is also expected to ease tomorrow morning, but with significant spillover into the headwaters.

Trampers in the area were urged to look out for rapidly rising streams and rivers, as well as possible surface flooding and slips.

The MetService also has issued severe weather watches for Tararua, Wairarapa, Kapiti Horowhenua, Wellington, Marlborough, Buller, Westland, Fiordland, Christchurch, Canterbury Plains, Canterbury High Country, North Otago, Central Otago, Southern Lakes, Dunedin, Clutha, Southland and Stewart Island.

Conditions north of the country are better.

Auckland has a high of 20C today, and a cloudy morning will be followed by long fine spells. Similar conditions are expected in Hamilton, where there is a chance of a shower, however.

Whangarei has an expected high of 23C and overnight low 13C. Today will be mostly sunny, with westerly winds.

Those in Kaitaia and the Northland area are in for a mostly sunny day, and people in Tauranga will see clouds at times, and a high of 22C.

After brief morning rain in Gisborne, the day will be otherwise fine with north-westerly winds.

Palmerston North is also in for morning rain and chance showers today - as is Wellington, which will get strong northerlies, though.

Meanwhile, for those heading out on the water today, there is a strong wind advisory for Manukau Harbour, Waitemata Harbour, Hauraki Gulf and the area from Bream Head to Cape Colville.