Page 4 – Tropical cyclones
From about October to April, intense storms known as tropical cyclones occasionally form in the tropics to the north of New Zealand. Generally much smaller than a typical low in New Zealand’s latitudes, they can have much lower pressures as well as hurricane-force winds and extremely heavy rain.
Normally, these cyclones rapidly weaken as they move towards New Zealand over cooler seas. However, if they meet a cold front, they can be transformed into very large and severe mid-latitude depressions.
Occasionally, one of these storms will pass over New Zealand bringing some of the most destructive weather experienced in the country, including widespread flooding and damaging winds.
In April 1968, Cyclone Giselle brought flooding and destructive winds to many parts of New Zealand. The inter-island ferry Wahine sank in Wellington Harbour, with the loss of 51 lives.
Twenty years later, Cyclone Bola caused severe flooding in parts of Hawke’s Bay, Gisborne and Northland, as well as bringing damaging winds to central and western parts of the North Island.
Worst storm of the 20th century
The cyclone of February 1936 was probably the most destructive storm to hit New Zealand in the 20th century. The depression that crossed the North Island on the second and third of February 1936 brought widespread heavy rain, causing every major river in the North Island to flood. The Mangakāhia River in Northland rose by 19 metres.
Roads and railway lines were cut in hundreds of places by slips, washouts and inundation. One slip near Stratford was 500 metres long. Along the east coast, large waves on top of elevated sea levels caused widespread erosion. The wind blew in windows and destroyed buildings from Picton to Kaitāia and brought down hundreds of thousands of trees, cutting power, telephone and telegraph lines. A train was derailed near Makerua (now known as Ōpiki), just south of Palmerston North, when three carriages were blown down a bank.
Two people died of hypothermia in the Tararua Range north of Wellington where, at the height of the storm, trees were uprooted from ridges and thrown into valleys. In Auckland 40 boats were sunk or driven ashore in the Waitematā Harbour, and several more sank in the Manukau Harbour.
Disaster was narrowly averted when the interisland ferry Rangatira steamed onto rocks on Wellington’s south coast. After being stuck fast for 20 minutes, the Rangatira was able to reverse off, then turn and back slowly up the harbour.