Summer has finally arrived and will last a good three days, the MetService says.

An anticyclone is moving slowly over the country over the next few days and is likely to bring the hottest days of summer yet, spokesman Bob McDavitt said.

"Day-time air temperatures are forecast to get into the 30s for people in the inland basins of the South Island," he said.

The hot weather was expected to last until the weekend.

The forecast for Waitangi Day celebrations in the Bay of Islands was for sun with a scattering of cloud, an onshore breeze, with temperatures around 23degC.

The weather was also looking great for the rugby sevens in Wellington on Friday and Saturday.

"Still conditions on Friday may help the heat build in the stadium, and an increasing northerly breeze is forecast to provide some relief on Saturday," Mr McDavitt said.

"The best way to beat the heat is to drink more water than usual and avoid full sunlight."

A southerly change on Sunday was expected to bring cooler conditions over the whole country.

- NZPA