The small central Otago town of Clyde took the award for being the hottest place in the country last month. The temperature there hit 35.5C on February 3.
In contrast, the coldest day was felt in Manapouri, in Fiordland, where the temperature dropped to 1.9C on February 10.
Niwa said an increase in air flow from the tropics last month brought down warm and humid air leading to muggy conditions, particularly in the North Island, and hotter days in the rest of the country in general.
"The moist tropical air masses (including remnants of tropical cyclones Tatiana and Winston) that affected New Zealand in February not only brought warm temperatures and high humidity, but also significant rainfall to some parts of the country," its report said.
Of the six main centres Auckland, Tauranga, Hamilton, Wellington, Christchurch and Dunedin the City of Sails was rated the warmest last month. Dunedin was the coolest, while Christchurch took the gong for being the driest place.
Wellington was the sunniest city and Tauranga the wettest and with the most cloudy periods.
Mean temperatures:
• Auckland: 22.3C (3rd highest on record)
• Tauranga: 21.7C (2nd highest on record)
• Hamilton: 21.3C (2nd highest on record)
• Wellington: 19.6C (highest on record)
• Christchurch: 19.2C (3rd highest on record)
• Dunedin: 17.7C (highest on record)
Source: Niwa