Have you ever wondered about the differences between cyclones, typhoons and hurricanes? It is all due to their location. When they occur in the South Pacific and Indian Oceans, we call them cyclones. The same type of storm in the Northwest Pacific is called a typhoon. In the Atlantic and Northeast Pacific, they’re called hurricanes.
What is a cyclone?
A warm-core cyclone (or tropical cyclone) is a spinning storm that occurs when warm air over the ocean and near (but not over) the equator becomes heated and rises quickly. As this air rises, it picks up water and water vapour, forming thunder clouds.
The rising air also leaves low-pressure areas (or a vacuum), which cooler air rushes in to fill. This new air then spirals upwards with immense force, moving faster as it moves upwards, creating a huge circle that can be hundreds of kilometres in diameter.
Warm-core cyclones are characterised by strong howling winds and heavy downpours of rain. There are also other types of cyclones, such as polar cyclones and extra-tropical cyclones, which are created a little differently.
Hurricanes and typhoons in the northern hemisphere blow in an anti-clockwise direction. The southern hemisphere’s cyclones blow in a clockwise direction. The rotation of the cyclones is caused by the rotation of the Earth. The reason the rising warm air must be a certain distance away from the equator (not less than 500 km) is so the rotation of the Earth can give direction to the flowing air mass. This is known as the Coriolis force. Closer to the equator, this effect becomes negligible, with more simple changes in air pressure driving storms.
A cyclone has an ‘eye’. This is the centre of the storm and is often calm and cloudless. However, this calm is short lived for those below, as the winds around the eye of the storm can reach speeds of over 200 km/h.
Have you ever wondered what is it like to be in a cyclone? Watch as Nigel Latta uses a wind tunnel to model hurricane strength winds.
Nature of science
Meteorologists can usually begin to make storm predictions about a week before a cyclone begins. Satellite images and computer modelling help to predict the storm’s intensity and path of travel or trajectory. While meteorologists provide information about potentially damaging weather, it is up to government officials to act on the warnings.
Naming cyclones, hurricanes and typhoons
Cyclones, hurricanes and typhoons have been given names for several centuries. They were most commonly named after the locations that were affected. Historians believe that Australian Clement Wragge was the first to use personal names in 1887. This practice finished when Wragge retired in the early 1900s. The current system began again in 1945, with United States Army Air Forces weather forecasters naming extreme weather events after their wives and girlfriends. Within a few years, this became the norm, with a new set of names developed annually. Eventually, regional meteorological services took over naming cyclones in their areas. Female names continued to be used. In 1975, the New Zealand Meteorological Service decided to include men’s names in the naming list – and soon after, other services did the same. The naming systems also became more inclusive to better reflect the regions’ cultures and languages.
Worldwide, the names are listed in alphabetical order. Some regions begin with a new list each year and recycle the names on a 6-year rotation. Other regions (New Zealand included) have lists of names that are used sequentially – a new list begins only when the old list is finished. The World Meteorological Organization removes the names of deadly or costly storms (like Katrina in the US or Tracy in Darwin) from the lists.
Some significant South Pacific Cyclones
Cyclone Gita (2018) was a category 5 storm with winds up to 230 km/h. It affected multiple island nations and territories. Tonga was the most severely hit and had 2 storm-related deaths.
Cyclone Winston (2016) was a category 5 storm with winds up to 285 km/h. It caused an estimated NZ$1.9 billion in damages and resulted in 44 casualties in Fiji. It is the strongest and costliest cyclone in South Pacific history.
Cyclone Pam (2015) was a category 5 storm with winds up to 280 km/h. It caused an estimated NZ$370 million in damages and resulted in 16 casualties in Vanuatu.
Cyclone Evan (2012) was a category 4 storm with winds up to 230 km/h. It caused an estimated NZ$200–300 million in damages and resulted in 14 casualties in Samoa.
Cyclone Wilma (2011) was a category 4 storm with winds up to 215 km/hr. It caused an estimated NZ$25 million in damages and is the first known tropical cyclone to hit New Zealand. (The others had transitioned into extra-tropical cyclones before they struck here.)
Cyclone Yasi (2011) was a category 5 storm with winds up to 285 km/h. It caused nearly NZ$5 billion in damages and was responsible for one indirect death in Australia.
Cyclone Bola (1988) was a category 4 storm with winds up to 195 km/h. It caused an estimated NZ$112 million in damages and resulted in three casualties in New Zealand. Cyclone Bola produced some of the largest rainfall totals for a single storm in New Zealand’s history. (It was a true 'weather bomb' as explained in the article Extreme weather.)
Cyclones and climate change
Scientists are not sure whether climate change will increase or decrease the number of cyclones, but they are expected to intensify.
Cyclones are just one of many different types of natural disasters that New Zealanders may face. Use the activity Home disaster kit to prepare for an emergency.
The history of naming hurricanes and cyclones – and the storms caused by this practice – is found in the article Historical tropical cyclone names. Significant hurricanes are named by region.
The World Meteorological Organization has world lists of tropical cyclone names.
Read about Cyclone Bola in this Napier City Council account.