Dunedin was the cloudiest of the six main centres last month, but slightly warmer than usual.
Niwa's May weather summary released yesterday says it was wetter than usual for Central Otago, Fiordland, the Southern Lakes and the West Coast.
Dunedin recorded near normal rainfall. Much of the North Island was drier than usual, in what was a month of contrast in rainfall.
Dunedin was slightly warmer than its May average, while sunshine hours were higher than usual.
On May 24, a southerly front struck, dropping temperatures in Dunedin from 15degC to 5degC in just five minutes.
Part of a cold snap in the last week of the month, it brought snow to sea level in Dunedin and Invercargill, and lightning strikes to parts of the South.
The country's coldest spot was Middlemarch, which recorded -7.4degC on May 30.
The biggest one-day rainfall was 256mm in Milford on May 22. Fiordland received more than twice as much rain as usual last month.