Last year was the third-warmest on record for New Zealand, based on Niwa's seven-station temperature series which started in 1909.
The nationwide average temperature for 2013 was 13.4 degrees Celsius, 0.8C above the 1971-2000 annual average.
Between January and April the weather was dominated by one of the most extreme droughts on record in New Zealand, which affected the North Island and Westland, Niwa said in its Annual Climate Summary published today.
The drought was caused by persistent slow-moving, or blocking, high pressure systems over the Tasman Sea and New Zealand during summer. That stopped low pressure systems and fronts from approaching the North Island.
After the drought, the remainder of the year had been rather changeable, with May and June having more southeasterly airflows than usual, and July and October having strong northwesterly airflows, Niwa said.
"Sea-surface temperatures around New Zealand were higher than normal throughout the year, which combined with the northerly flow anomaly will have contributed to the warm mean air temperatures observed throughout the country in 2013."
January, July, September and October were also unusually windy, but from February to May the country went through a particularly calm period. The year as a whole was less windy than average.
Wind caused widespread damage across Wellington during a storm in June. Wellington Airport had its strongest sustained 10-minute winds since 1985.
A severe windstorm in Canterbury in September broke numerous gust records for the month, damaging more than 800 irrigators.
Annual temperatures were specially high in parts of southern Northland, Hawke's Bay, Manawatu, Wairarapa, Banks Peninsula and western Southland, with annual mean temperatures at least 1C above the annual average, Niwa said.
It was the warmest year on record for Tauranga, Masterton, Dannevirke, Ngawi, Hastings, Waipawa, Palmerston North, Stratford, Hawera, Whanganui, Farewell Spit, Reefton, Secretary Island, Nelson, Cheviot, Wanaka, and Gore.
Places with the highest mean maximum temperatures for the year were Kerikeri, Tauranga, Ruakura, Turangi, Masterton, Dannevirke, Hicks Bay, Waipawa, Palmerston North, Stratford, Farewell Spit, Westport, Reefton, Nelson, Christchurch, and Tiwai Pt.
Along with the warmth and drought, there was also one of the "most intense" rainstorms ever measured in this country.
For Nelson and Tasman, the rainstorm in April was the most intense ever recorded.
In the Roding catchment near Richmond 101 millimetres was recorded in an hour, a rate with a 500-year return period for the area, Niwa said.
The most extreme one-hour rainfall ever measured in this country was 134mm an hour in the Cropp river catchment on the west coast of the South Island, which held many of the country's extreme rainfall records.
Less than 80 per cent of annual normal rainfall was recorded for parts of Northland, Waikato, Bay of Plenty, Taranaki, and isolated areas of the West Coast.
It was the driest year on record for Dargaville, Toenepi near Morrinsville, Taupo and Turangi - with between 67 per cent and 72 per cent of normal.
Marlborough, North Canterbury and North Otago had above normal rainfall.
Last week, climate scientist Jim Salinger released his own calculations which put 2013 as New Zealand's second-warmest year since reliable records started in 1870, with an annual regional mean temperature 0.84C above the 1961-1990 long-term average of 12.17C.