May 1966: Barometers were low over and to the east of the North Island, and there was an unusually high frequency of southerly to easterly winds. It was a cold month but conditions were particularly pleasant on the West Coast. Farmers found it a good month for stock, though growth was affected in some areas by frosts, and in Northland and Auckland the ground was becoming rather too wet.
Rainfall: On the West Coast it was by far the driest May on record, with less than 1/4 of the average rainfall. It was also exceptionally dry in the Alps, the Canterbury high country, and Central Otago. Rainfall was also somewhat below average in Southland and Nelson and in the North Island west of the main ranges from Hamilton and Opotiki to Levin. In eastern districts from Oamaru to East Cape, about Cook Strait, and in Northland and Auckland rainfall was above average. The surplus exceeded 50% in Wairarapa, Wellington, most of Marlborough and the North Canterbury coast, also in Coromandel. Over most of Marlborough 2/3 of the month’s rain, amounting to 4-10” fell on the 23rd during the passage of a deep depression across the North Island. Flooding disrupted road and rail transport on the Kaikoura Coast.
Temperatures: Temperatures were mainly below average by about 1F-2F, highest departures being in Manawatu. On the West Coast they were close to average. The second half of the month was much colder than the first half. Two spells of cold southerlies brought snow to the ranges and some of the North Island high country form the 17th-20th and on the 25th-26th, respectively.
Sunshine: Northern and western districts of both islands together with parts of Southland were favoured with more sunshine than usual, mainly by 20-30 hours. Eastern districts from Balclutha to East Cape were less than average by a similar amount.
[Some totals: Kaitaia 147, Kerikeri 145, Whangarei 135, Auckland 171, Tauranga 194, Whakatane 195, Taupo 166, Opotiki 183, Hamilton 176, New Plymouth 189, Masterton 110, Gisborne 100, Napier 133, Wairoa 102, Paraparaumu 156, Ohakea 163, Palmerston North 145, Foxton 176, Levin 162, Wellington 116, Stratford 175, Ohakune 137, Wanganui 153, Westport 150, Hokitika 156, Greymouth 137, Haast 152, Riwaka 181, Nelson 180, Blenheim 173, Grassmere 157, Kaikoura 114, Mt Cook 108, Mt John 150, Methven 129, Christchurch 109, Tekapo 127, Timaru 124, Waimate 99, Dunedin Aero 76, Dunedin 73, Oamaru 109, Queenstown 89, Alexandra 102, Invercargill 109, Campbell Is 14, Chatham Is 88].
Sources: NZ Met. Misc. pub. 107 (Climatological table, NZ Gazette) and NZ Met. Misc. pub. 109 (Meteorological Observations) - additional comments by the poster.