Cyclone

A tropical cyclone is a cyclone of tropical origin of small diameter (some hundreds of kilometres) with a minimum surface pressure in some cases of less than 900 hPa, very violent winds and torrential rain; sometimes accompanied by thunderstorms. It usually contains a central region, knows as the ‘eye’ of the storm, with a diameter of the order of some tens of kilometres, and with light winds and a more of less lightly clouded sky (WMO, 2017).

Hurricanes, tropical cyclones and typhoons affect millions every year, and are likely to become more severe in the future although possibly less frequent due to global warming.

Tropical cyclones, hurricanes and typhoons, although named differently, describe the same hazard type. They are referred to as tropical cyclones in the Indian Ocean and South Pacific, hurricanes in the Atlantic and eastern North Pacific, and typhoons in the western North Pacific. In the north Atlantic and the Caribbean, August and September are usually peak months of the hurricane season, which spans from June through to November. In the eastern North Pacific, the season starts in mid-May and finishes in November. The North Indian Ocean cyclone season is between April and December, with peaks in May and October.

Tropical cyclones are often difficult to predict, because they can suddenly weaken or change their course. However, meteorologists use state-of-art technologies and develop modern techniques such as numerical weather prediction models to predict how a tropical cyclone evolves, including its movement and change of intensity, when and where one will hit land and at what speed. Official warnings are then issued by the National Meteorological Services of the countries concerned (WMO).

Risk factors

  • Climate change: Due to warmer global temperatures, the proportion of high-intensity cyclones has increased. Also, cyclones are likely to move slower on land, and thus become more devastating.
  • Environmental degradation: Deforestation creates a warm area that draws in sea breezes from the ocean during the daytime, producing moisture, and leading to storms. In turn, rising waters can make wastewater treatment plants, sewers, hazardous waste sites, agricultural lands and animal feeding operations overflow, carrying pollutants into waterways.
  • Coastal development, including urbanization in coastal areas: Apart from increasing its exposure to coastal hazards, a city’s impervious sidewalks and streets increase, heavy rainfall can not be absorbed into the ground.

Vulnerable areas

  • Coastal areas are the most cyclone-prone.
  • Tropical cyclones are generally accompanied with heavy rains and severe flooding.
  • Coastal areas with shallow slant bathymetry and flat plain, with storm surges that may threaten tens of thousands of people living by the sea.
  • The most vulnerable populations are those who are living in poor buildings and fragile constructions in the coastal zones.
  • The Small Island Developing States are also vulnerable because some might be indebted, their economies undiversified and hazard events can affect the whole territory.

Saffir-Simpson hurricane scale

Hurricanes are ranked according to the Saffir-Simpson hurricane scale, which classifies the damage caused by hurricanes to wind speed. Hurricanes can inflict terrible damage even from their formative stage.

Risk reduction measures

  • Evacuation exercises to ensure full community participation.
  • Structural measures to withstand/lessen the impact of winds and flooding.
  • Land use control and limiting the exposure of critical assets.
  • Integrate flood risk assessment into urban planning strategies.
  • Avoid building directly on the coastline.
  • Maintain wind-proof buildings for community shelters.
  • Use of flood-resistant material in construction.
  • Grey infrastructure: sea walls revetments, protective embankments, levees and dikes.
  • Natural infrastructure: mangroves, coral reefs, wetlands and forests.
  • Education: information on cyclones and protection from cyclone damage in school and social activities.
  • Protect and evacuate animals.

Latest Cyclone additions in the Knowledge Base

Antigua and Barbuda Hurricane Damage
Research briefs
Galveston Island was used as an example to predict damage that would occur as a result of hurricanes of varying intensities.
Texas A&M University System
Update
Fighting between armed gangs has utterly upended life in Haiti, making it even harder to cope with the tropical cyclones that are becoming more frequent and severe because of climate change.
Context
Update
Schools were closed for several days as temperatures soared to over 40 degrees Celsius in April and May. Now they are due to reopen after the holidays in July, rather than August, as authorities rework the education calendar to adapt to extreme weather.
Context
Update
The United Nations World Food Programme (WFP) called for urgent global support for small island nations disproportionately impacted by the climate crisis, with many bracing for what is expected to be an intense and destructive Atlantic hurricane season.
World Food Programme
African students using water taps
Update
A severe storm hit South Africa’s Western Cape province between 6 and 9 April 2024, with extreme winds gusting at up to 135km/h. The storm left a trail of destruction across Cape Town and surrounding areas.
Conversation Media Group, the
Update
While Atlantic hurricane season runs June 1 to November 30, at USAID, we work year-round to help our neighbors in the region, providing them with the tools and skills needed to be ready for and more resilient to natural hazards.
United States Agency for International Development (USAID)
Meteorological map of hurricane
Update
In 1955, Diane became known as the first billion-dollar storm. The compound impacts prompted Congress to fund major studies of hurricane meteorology and protection efforts.
Conversation Media Group, the
Update
La Nina and warmer-than-average ocean temperatures will be major drivers of tropical activity.
National Oceanic and Atmospheric Administration

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