Under the influence of the concentrated air flow channelled through Cook Strait, Wellington has a well-deserved reputation for windiness. During the day only 15 per cent of the winds fail to reach 5 miles per hour and, of the remainder, 47 per cent are from N or NW and 29 per cent are from S or SE. Gales, accompanied by gusts up to 60 miles per hour, occur on about 30 days per annum and are most frequent in the spring and summer. Gusts to 90 miles per hour are comparatively rare in the city itself, but much higher speeds have been recorded in adjacent exposed places.
Rainfall measured at Kelburn averages 49 in. per annum. The driest period is from January to March, each month averaging 3 in. Winter is the wettest season, each of the months June to August averaging 5 in. Rain falls on 159 days per annum, and on 97 of these the amount reaches 0.1 in. Once in 20 years a fall of 5.5 in. may occur within 24 hours, and 1.1 in. in one hour. In the last 100 years the longest period without rain was 34 days.
January and February, each with a mean temperature of 61 °F, are the two warmest months, and July (47°F) is the coldest. In January the daily maximum averages 68°F, and the minimum 55°F; in July the corresponding daily range is from 51°F to 42°F. The extreme range is small; 80°F is reached only once in two years, while air temperatures below freezing point (32°F) do not occur at Kelburn, 415 ft above sea level. In more sheltered areas and in the Hutt Valley winter nights are colder and frosts occur on most calm, clear nights between May and September. Rainfall also varies considerably; in Lyall Bay and Miramar it averages 40–50 in. per annum, while the Hutt Valley has 50–55 in. and Wainuiomata about 70 in. Sunshine in summer is 50 per cent of the possible amount; in winter increased cloudiness reduces it to 40 per cent. For the year the average duration is 2,000 hours. Residents on the hills above 500 ft occasionally find themselves in cloud, but fog in the central city area is rare. Hail showers occur on about 12 days per annum, mostly in winter, but hail damage is negligible. Thunder is heard briefly on about five days. The city streets are never seen under snow.