Long weekend weather: Wet in the west, mainly fine in the east

An assortment of weather is forecast for Anzac weekend - with rain and a risk of thunderstorms in the west and mainly fine conditions in the east.

Six60 concertgoers in Auckland have been told to expect "a few showers" during the Saturday gig, while boaties on western coastlines from Fiordland to Northland have been warned of heavy swell.

MetService meteorologist Alwyn Bakker said a front tracking across Aotearoa on Friday will bring rain for the west of both islands and risk of thunderstorms.

"[There is a] possibility of peak rain rates of 10-25mm an hour. However, the eastern areas of both islands will stay mainly fine."

Heavy rain watches have been issued for Fiordland, north of the Doubtful Sound and the ranges of Westland, south of Otira.

On Saturday, a ridge is set to develop and drive away most of the rain, but those attending the Six60 concert in Auckland on Saturday evening should pack an extra layer and prepare for the odd shower.

Anzac Day dawn services on Sunday around the country should stay mainly dry but those in Auckland, the lower North Island, and Christchurch could see a few showers.

The ridge weakens on Sunday while a front travels over the South Island, and the North Island on Monday, with rain and a cool southwesterly in its wake.

Single-digit overnight temperatures are expected for most, with frosts in parts of the South Island, especially inland and sheltered areas.

Heavy swell

Large waves are expected along the western coastlines of both islands over the weekend.

Meteorologist Tahlia Crabtree said the waves will have a long swell period, giving them more energy than average swells.

"Boaties should take extra care going out on the water in affected waters this weekend."

Anyone visiting beaches along the western coasts of both islands over the long weekend is advised to take care as long swells can create strong and dangerous rip currents.

Waves of up to 9m are possible in the Far South from Friday evening, moving up the coast before gradually lowering to 4m off the Auckland west coast on Saturday.

Anzac Day forecasts

Kaitaia Mainly fine, one or two showers. Westerlies. 20C high, 12C low.

Whangārei Mainly fine, but chance shower. Westerlies. 20C / 11C.

Auckland Cloudy periods and isolated showers clearing. Westerlies. 19C / 13C.

Hamilton Mainly fine, chance morning shower. Westerly breezes. 19C / 8C.

Tauranga Mainly fine. Westerlies. 20C / 10C.

New Plymouth Mainly fine, chance morning shower. Westerly breezes. 18C / 11C.

Rotorua Mainly fine. Westerlies. 17C / 7C.

Napier Fine. Westerlies. 21C / 10C.

Wellington Morning cloud, isolated showers, then fine. Southerlies tending northerly by afternoon. 16C / 11C.

Nelson Fine. Light winds. 18C / 8C.

Christchurch Morning cloud, then fine. Northerlies developing. 18C / 5C.

Dunedin Mainly fine. Northerlies. 16C / 6C.