December 1958: Warm, unsettled conditions predominated. Over most of the North Island it was wet and dull, but it was much sunnier in eastern and southern districts of the South Island. More rain would have been welcomed in Canterbury to offset the effects of the very dry spring. In parts of the North Island conditions were too wet for sheep. Heavy rains in the Taupo catchment area ended a long period of power restrictions. Heavy rains in the Taupo catchment area brought to an end a long period of electric power restrictions. A northwesterly gale caused some damage in Christchurch and other parts of Canterbury on the 12th.
Rainfall: It was a very wet month over the North Island (except the Gisborne district) and in Nelson, few places having less than double the normal rainfall. From Taranaki across to Rotorua and Taupo, with totals 3-4 times the average, it was the wettest December on record. The only serious flooding occurred on the 24th, when slips and washouts disrupted road and rail traffic in the centre of the Island. [New Plymouth had 23.31” (592mm) for the month, with 7.04” (179mm) on the 23rd]. Over most of the South Island and in Gisborne rainfall was a little above average, but in mid-Canterbury and near the southeast coast it did not quite reach the average. In a thunderstorm on the 16th in the Levin-Otaki area hailstones of 1/2” in diameter caused serious damage to fruit crops.
Temperatures: Temperatures were about 3F above normal in the North Island and the northern part of the South Island. From there the departure decreased southward and was only about 0.5F on the Southland coast.
Sunshine: Sunshine totals were low except in eastern and southern districts of the South Island, where they were close to average. In central and northern districts of the North Island the deficiency ranged up to 2 1/2 hours a day, making it one of the cloudiest Decembers on record in the area. New Plymouth and Tauranga have not previously recorded such low totals.
[Some totals: Te Hapua 158, Kaitaia 161, Kerikeri 146, Whangarei 148, Auckland 151, Tauranga 175, Whakatane 189, Taupo 147, Hamilton 146, New Plymouth 144, Masterton 194, Gisborne 219, Napier 186, Paraparaumu 180, Ohakea 195, Palmerston North 160, Levin 145, Wellington 188, Wanganui 191, Westport 162, Hokitika 166, Greymouth 138, Haast 164, Nelson 199, Blenheim 235, Grassmere 221, Mt Cook 150, Methven 205, Christchurch 212, Tekapo 222, Timaru 194, Waimate 153, Omarama 197, Dunedin 190, Queenstown 233, Alexandra 208, Invercargill 187, Raoul Is 260].
Sources: NZ Met. Misc. pub. 107 (Climatological table, NZ Gazette) and NZ Met. Misc. pub. 109 (Meteorological Observations) - additional comments by the poster.