January 1956: An exceptionally warm month. Drought conditions developed from Canterbury southwards following several months of low rainfall and warm temperatures, but good rains at the end of the month brought welcome relief to all but North Canterbury. In the North Island stock conditions were good and stone fruits ripened very early. A strong NW gale on the 30th caused some minor damage in the vicinity of Cook Strait.
Rainfall: Rainfall was less than half normal in Gisborne and North Canterbury. Southland and Wairarapa also received somewhat less than the normal rainfall. It was wetter than usual in Northland, Wellington and the Marlborough Sounds; many places in these areas received more than twice the average rainfall. An exceptionally high total of 33” was recorded at Tuna Bay in the Marlborough Sounds.
Temperatures: Temperatures were everywhere far above normal. For the country as a whole there has not hitherto been a warmer month, with the possible exception of February 1938. For the South Island alone it was easily the warmest month on record, the departure being as much as 6F to almost 9F in Canterbury and Otago.
[The national average was surpassed by February 1998 (mean 19.7C) by 0.5C; January 2018 set a new record with 20.3C. Until January 2018 Central Otago had January 1956 as its hottest month, but this has now been surpassed by about 0.4C.]
In the period from the 15th to the 24th some exceptionally high maximum temperatures were recorded in eastern districts of both Islands. The temperature of 101.2F at Ashburton the 19th was the highest ever officially recorded in this country [remained so until 7/2/1973], and a new record for the North Island was established with 99.8F at Gisborne on the 22nd [ditto].
Sunshine: Sunshine was below normal over the North Island and northern parts of the South Island. North of Wanganui deficiencies ranged from 70 hours to about 120 hours. Record low totals included 163 at Tauranga, and 160 at New Plymouth. The remainder of the South Island had more sunshine than usual and south of Christchurch departures were mainly above 40 hours. Invercargill had the unusual distinction of being one of the sunniest places in the country – its total of 250 hours was the highest there in any month in over 40 years of record.
[Record surpassed in 1999, then easily beaten in 2008 (287).]
[Some totals: Te Hapua 164, Kaitaia 157, Kerikeri 153, Whangarei 153, Auckland 166, Tauranga 163, Taupo 134, Hamilton 128, New Plymouth 160, Masterton 199, Gisborne 225, Napier 190, Paraparaumu 152, Ohakea 184, Palmerston Nth 157, Levin 141, Wellington 179, Wanganui 185, Westport 167, Hokitika 217, Greymouth 189, Haast 230, Nelson 193, Blenheim 220, Grassmere 226, Mt Cook 156, Methven 262, Christchurch 228, Tekapo 270, Timaru 247, Waimate 236, Omarama 245, Dunedin 221, Queenstown 270, Alexandra 261, Invercargill 250, Campbell Is 105].
Sources: NZ Met. Misc. pub. 107 (Climatological table, NZ Gazette) and NZ Met. Misc. pub. 109 (Meteorological Observations) - additional comments by the poster.