Timaru hit 30.8C on April 4 and Christchurch had the second-warmest April since records began in 1863.
The atypical warmth also caused coastal sea temperature anomalies to spike, ranging from 0.5 to 1.3C above average around the country for the month.
Niwa meteorologist Ben Noll said climate change is embedded within the weather patterns we are experiencing.
"It's not that one single event here is being caused by climate change, but climate change is influencing each of those events in a different way.
"In a warming world, we expect more high-temperature extremes. The way this summary illustrates that is there were heaps, three dozen, warm-temperature extremes, but zero low-temperature extremes. That type of statistic is consistent with a warming earth."
Seven locations saw near-record dryness, including Dunedin with an equal-driest month on record and Wellington with its 4th driest April on record.
By the beginning of May, soil moisture levels were in severe deficit across the eastern North Island and eastern and interior South Island, especially in Gisborne, Hawke's Bay, Canterbury, Otago and Southland.
April 4 was also the date of the highest one-day rainfall with 126mm recorded at Milford Sound as well as the day strong northwesterly winds flipped caravans in Wellington and in Canterbury, while fanning several wildfires in the South Island.
Strong winds also downed trees and power lines in the Temuka area on April 4, causing a few hundred power outages.
On April 10, heavy rainfall and wind battered parts of the country as a subtropical low-pressure system approached. Niwa noted that police attended a spate of car crashes that day – including 18 in Auckland alone.
