A tropical cyclone heading for Raoul Island, about 1100km northeast of New Zealand, is weakening but may cause minor damage, forecasters warn.

Tropical Cyclone Bune weakened slightly this afternoon to a strong category 2 cyclone, with its winds of 111km/h just under category 3, WeatherWatch head weather analyst Philip Duncan said.

The cyclone stalled today, but was likely to pass over or near Raoul Island, part of the Kermadecs. Department of Conservation volunteers work on the island in groups of up to 10.

"It's unclear how many are currently on the island, however the cyclone should have weakened to a category 1 storm when it passes over," Mr Duncan said.

A category 1 cyclone could fell trees, cause minor damage to structures, and break boats from their moorings.

The storm is expected to reach New Zealand next week, although severe weather was unlikely as the centre was not going to make landfall, he said.

There was a strong chance it would create dangerous rips and surf along the east coast, particularly from East Cape to Wairarapa, between Tuesday and Saturday.