New Zealand had the ninth warmest August on record, with temperatures 0.5 to 1.2C above average.
The warmth was caused by west and northwest winds flowing across warm seas, Niwa said.
The Whanganui region had 120 to 140 per cent more rain than usual. On August 6 there was an avalanche at the Turoa ski area, and the Desert Road was closed by snow and ice on August 23-24.
Water restrictions
Hunterville and Mangaweka residents are asked to conserve water until further notice.