New Zealand lies in the path of the roaring forties – the persistent westerly winds that prevail between 40º and 50º South. The central ranges deflect these winds through Cook Strait, the narrow gap between the North and South islands. Funnelled through this passage, they become stronger. Wellington is in the teeth of these winds.
Gusty north-westerlies alternate with southerlies. North-westerly winds predominate in spring and summer, while southerlies are most common in winter. Records show that in one year, northerlies and north-westerlies blew for 61% of the time and southerlies for 28%. Gusts of more than 60 kilometres per hour are recorded nearly every second day – 173 days a year on average – compared to just 30 days for Rotorua and 35 for Nelson.
On rare occasions, tropical cyclones stray south and become severe storms in Wellington. In February 1936 a storm drove ships aground in the harbour and flattened forest in the Tararua Range. In April 1968 a hurricane-force southerly drove the ferry Wahine onto rocks at the harbour’s entrance. Fifty-one lives were lost. The same day, Ōteranga Bay (on the shore of Cook Strait) was hit by a 267 kilometre-per-hour gust – the highest ever recorded in the region.
Wellington’s most brutal winds usually come from the south, dragging cold air up from the Southern Ocean, blasting the region and sometimes leaving snow on the higher hills.
Temperature and sunshine
The city’s average daily temperature is 12.8º C (slightly above the national average) and it averages 2,055 hours of sunshine a year – a similar amount to Auckland and Christchurch.
The changing climate
In the past, the climate was more severe. The ice ages (the most recent ending 10,000 years ago) caused the sea level to drop more than 100 metres as water was absorbed by extensive polar ice caps. During the coldest phase (about 25,000–15,000 years ago), the sea retreated and much of Cook Strait became a plain stretching far to the west. In the mountains, glaciers formed, and traces of them can still be seen in the Tararuas. The rise and fall of the sea level is evident in coastal terraces such as Tongue Point, on the south coast.
Wellington city receives an average of 1,207 millimetres of rain each year – the national average is about 1,400 millimetres.