3.1 Tropical cyclones and hurricanes
4 min read•august 14, 2024
Tropical cyclones and hurricanes are powerful storms that form over warm ocean waters. These intense weather systems can cause devastating impacts on coastal areas, including , high winds, and heavy rainfall.
Understanding the formation, structure, and behavior of tropical cyclones is crucial for predicting their paths and impacts. This knowledge helps meteorologists develop better forecasting tools and early warning systems, ultimately saving lives and reducing damage in vulnerable communities.
Formation and Life Cycle of Tropical Cyclones
Conditions for Tropical Cyclone Formation
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- Tropical cyclones form over warm ocean waters near the equator requiring a sea surface temperature of at least 26.5°C (80°F) to a depth of 50 meters
- The formation involves the convergence of warm, moist air near the surface creating an area of low pressure and rising motion known as a
- As the warm air rises and cools, water vapor condenses releasing latent heat and further fueling the rising motion leading to the development of thunderstorms and a rotating system
Structure and Stages of Tropical Cyclones
- The structure of a mature consists of a calm, clear at the center surrounded by a circular eyewall where the strongest winds and most intense rainfall occur
- Spiraling rain bands extend outward from the eyewall characterized by heavy precipitation and strong winds
- The life cycle can be divided into four stages: tropical disturbance, , , and ( in the western North Pacific)
- A tropical disturbance is an area of low pressure with thunderstorms but no closed circulation
- A tropical depression forms when the low-pressure system develops a closed circulation with sustained winds up to 38 mph (61 km/h)
- A tropical storm is characterized by sustained winds between 39 and 73 mph (63 to 118 km/h) and a more organized structure
- A hurricane (typhoon) has sustained winds of 74 mph (119 km/h) or higher and a well-defined eye and eyewall
Factors Influencing Tropical Cyclone Intensity
Key Factors Affecting Intensity
- The primary factors influencing the intensity are sea surface temperature, atmospheric moisture, and vertical
- Warmer sea surface temperatures provide more energy for the cyclone to develop and intensify (Gulf of Mexico, Caribbean Sea)
- High atmospheric moisture content allows for greater condensation and latent heat release fueling the cyclone's growth
- Low vertical wind shear (change in wind speed or direction with height) allows the cyclone to maintain its structure and intensify while high wind shear can disrupt the cyclone's circulation
- The , generated by the Earth's rotation, causes tropical cyclones to spin counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere
Factors Influencing Tropical Cyclone Movement
- The movement is primarily driven by the surrounding atmospheric circulation such as the steering winds in the mid and upper troposphere
- Other factors influencing the track include the presence of high and low-pressure systems, the position of the subtropical ridge, and the cyclone's interaction with land masses
- The describes the interaction between two nearby tropical cyclones which can cause them to rotate around each other or merge into a single system (Hurricanes Hilary and Irwin in 2017)
Impacts of Tropical Cyclones on Coastal Areas
Physical and Environmental Impacts
- Storm surge, the abnormal rise in sea level caused by the cyclone's low pressure and strong winds, can lead to severe coastal and erosion ( in 2005)
- High winds can cause extensive damage to buildings, infrastructure, and vegetation as well as generate wind-borne debris
- Heavy rainfall and inland flooding can occur as the cyclone moves over land leading to flash floods, river flooding, and landslides
- The combination of storm surge and heavy rainfall can overwhelm drainage systems and exacerbate flooding in low-lying areas (Houston during in 2017)
Socioeconomic Impacts
- Tropical cyclones can disrupt essential services such as electricity, water supply, and transportation networks hindering emergency response and recovery efforts
- Economic impacts include direct losses from property damage and indirect losses from business interruptions, reduced tourism, and decreased agricultural productivity
- Social impacts may include displacement of residents, loss of lives, injuries, and long-term mental health consequences for affected populations ( in Puerto Rico in 2017)
Forecasting and Early Warning Systems for Tropical Cyclones
Forecasting Techniques and Tools
- Accurate forecasting of tropical cyclone formation, intensity, and track is crucial for providing timely warnings to vulnerable communities
- Numerical weather prediction models, such as global and regional models, are used to simulate the atmosphere's behavior and predict the evolution of tropical cyclones (Hurricane Weather Research and Forecasting (HWRF) model)
- Satellite imagery, particularly from geostationary and polar-orbiting satellites, is essential for monitoring the development and movement of tropical cyclones
- Aircraft reconnaissance missions, such as the Hurricane Hunters, provide in-situ measurements of wind speed, pressure, and other parameters to improve the accuracy of forecasts
Early Warning and Risk Communication
- Early warning systems, including public advisories, watches, and warnings, are issued by national meteorological services to alert the public and emergency managers about the potential impacts of an approaching cyclone
- Risk communication strategies, such as targeted messaging and the use of multiple communication channels, are employed to ensure that warnings reach the intended audience and promote appropriate protective actions
- Evacuation planning and shelter management are critical components of tropical cyclone preparedness aiming to minimize the loss of life and ensure public safety (contraflow traffic patterns, designated shelters)
- Post-event assessments and research contribute to improving the understanding of tropical cyclone behavior, forecasting techniques, and risk reduction strategies
Key Terms to Review (26)
Category 1: Category 1 refers to the classification of tropical cyclones and hurricanes based on their wind speeds, specifically within the Saffir-Simpson Hurricane Wind Scale. This scale categorizes storms from 1 to 5, with Category 1 representing the lowest level of intensity in terms of sustained wind speeds ranging from 74 to 95 miles per hour. While Category 1 hurricanes can cause some damage, they are generally considered the least severe when compared to higher categories.
Category 5: Category 5 is the highest classification on the Saffir-Simpson Hurricane Wind Scale, indicating a hurricane with sustained wind speeds of 157 mph (252 km/h) or higher. Hurricanes in this category cause catastrophic damage, leading to complete destruction of buildings and infrastructure, along with severe flooding in coastal areas. The impacts of a Category 5 hurricane can result in significant loss of life and long-term economic disruption.
Coriolis Force: The Coriolis force is an apparent force caused by the rotation of the Earth, influencing the direction of winds and ocean currents. This force causes moving objects, such as air masses, to turn and twist instead of moving in a straight line, significantly impacting the development and movement of tropical cyclones and hurricanes. Understanding this force is crucial for predicting storm paths and behaviors, as it plays a key role in the dynamics of large-scale weather systems.
Disaster preparedness: Disaster preparedness refers to the proactive measures and planning processes designed to ensure that individuals, communities, and organizations are ready to respond effectively to various types of disasters. This involves assessing risks, developing emergency plans, conducting training, and establishing communication protocols to mitigate impacts when disasters strike. Understanding historical patterns of disasters, recognizing specific threats like tropical cyclones and hurricanes, and fostering collaboration between public and private sectors are all vital components of a comprehensive disaster preparedness strategy.
Disaster recovery planning: Disaster recovery planning is a strategic approach aimed at preparing for and responding to natural or man-made disasters to ensure the continuity of critical operations and services. It involves assessing potential risks, developing response strategies, and implementing procedures that can be activated when a disaster strikes. This planning is crucial for minimizing damage, protecting lives, and facilitating recovery, especially in the context of extreme weather events and building resilience for sustainable development.
Evacuation Plans: Evacuation plans are detailed strategies designed to guide individuals and communities in safely exiting an area that may be threatened by natural or man-made disasters. These plans are crucial for ensuring public safety, coordinating rescue efforts, and minimizing chaos during emergencies such as earthquakes, tsunamis, hurricanes, and nuclear incidents.
Evacuations: Evacuations refer to the organized process of moving individuals away from areas that are at risk due to natural disasters, such as tropical cyclones and hurricanes. This process is crucial for protecting lives and minimizing injuries during severe weather events. It often involves coordination among government agencies, emergency services, and community organizations to ensure a safe and efficient relocation of people to safer locations.
Eye: The eye is the calm, central region of a tropical cyclone, including hurricanes, where the weather is relatively clear and the winds are light. It is surrounded by the eyewall, which is a ring of towering thunderstorms that produces the most intense winds and rainfall. The eye can vary in size and shape, but it is crucial for understanding the overall structure and behavior of these powerful storms.
Flooding: Flooding refers to the overflow of water onto land that is typically dry, often caused by excessive rainfall, storm surges, or the rapid melting of snow. It can lead to significant damage to property, infrastructure, and ecosystems, and can cause loss of life. In certain contexts, flooding can occur as a result of natural disasters such as tsunamis and tropical cyclones, making it crucial to understand its dynamics and impacts.
Fujiwhara Effect: The Fujiwhara Effect is a meteorological phenomenon that occurs when two tropical cyclones, or hurricanes, come close to each other and interact through gravitational attraction and rotational forces. This interaction can lead to a change in the paths of the cyclones, causing them to either orbit around each other or merge into a single, larger storm system. Understanding this effect is crucial in predicting the behavior of tropical cyclones, particularly in regions where multiple storms may form simultaneously.
Hurricane: A hurricane is a powerful tropical cyclone characterized by strong winds, heavy rainfall, and a well-defined center known as the eye. These storms form over warm ocean waters and can cause extensive damage when they make landfall, impacting both human and natural systems. Understanding hurricanes involves recognizing their classification within the broader category of disasters, their unique characteristics as tropical cyclones, and the necessity of effective disaster preparedness and response strategies to mitigate their impacts.
Hurricane Harvey: Hurricane Harvey was a Category 4 tropical cyclone that made landfall in Texas in August 2017, becoming one of the most destructive hurricanes in U.S. history. It brought unprecedented rainfall, leading to catastrophic flooding, especially in the Houston metropolitan area, and highlighted the significant impact of tropical cyclones on communities and infrastructure.
Hurricane Katrina: Hurricane Katrina was a devastating Category 5 Atlantic hurricane that struck the Gulf Coast of the United States in August 2005, particularly affecting New Orleans, Louisiana. The hurricane caused catastrophic flooding due to levee failures, leading to widespread destruction and loss of life, while also highlighting vulnerabilities in disaster preparedness and response systems.
Hurricane Maria: Hurricane Maria was a powerful and devastating Category 5 Atlantic hurricane that struck the Caribbean in September 2017, particularly impacting Puerto Rico. It caused catastrophic damage, resulting in widespread destruction of infrastructure, homes, and critical resources, highlighting the vulnerabilities of island nations to extreme weather events and the challenges faced in disaster response and recovery efforts.
Infrastructure damage: Infrastructure damage refers to the harm or destruction of essential physical structures and facilities that support a society's economy and quality of life, including transportation systems, utilities, communication networks, and public services. The extent of this damage can significantly influence recovery efforts, economic stability, and public safety in the aftermath of disasters.
Intensification: Intensification refers to the process by which a tropical cyclone or hurricane increases in strength, characterized by a rise in wind speeds and a drop in atmospheric pressure at its center. This phenomenon is crucial because it can lead to more severe weather conditions, increased rainfall, and heightened storm surge, which all contribute to the potential for greater destruction when the storm makes landfall. Understanding intensification helps in predicting storm behavior and preparing for its impacts on communities.
Ocean temperature rise: Ocean temperature rise refers to the increase in the average temperature of the Earth's oceans, primarily due to climate change caused by human activities such as burning fossil fuels and deforestation. This phenomenon plays a critical role in shaping weather patterns and influencing the formation and intensity of tropical cyclones and hurricanes, which thrive in warmer ocean waters.
Relief Efforts: Relief efforts refer to the coordinated actions and initiatives taken to provide immediate assistance to individuals and communities affected by natural disasters, such as tropical cyclones and hurricanes. These efforts aim to alleviate suffering, restore basic needs, and support recovery in the aftermath of such catastrophic events, involving government agencies, non-governmental organizations, and local communities working together.
Storm surge: A storm surge is an abnormal rise in sea level that occurs during a storm, particularly hurricanes and tropical cyclones, driven primarily by strong winds and low atmospheric pressure. This phenomenon can lead to severe coastal flooding, making it a critical concern in understanding the impacts of intense weather events. It often exacerbates the effects of heavy rainfall and high tides, significantly increasing the risk of flooding in coastal areas.
Tropical cyclone: A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, strong winds, and heavy rain, typically forming over warm ocean waters in tropical regions. These powerful weather events are known for their potential to cause significant destruction, particularly when they make landfall, impacting coastal communities and ecosystems.
Tropical Depression: A tropical depression is a weather system characterized by a low-pressure area with organized thunderstorms and maximum sustained winds of 38 mph (33 knots) or less. It is an early stage of tropical cyclone development, which can eventually intensify into more severe forms such as tropical storms and hurricanes if conditions are favorable. Understanding tropical depressions is crucial because they serve as indicators of potential future storms that can cause significant weather impacts.
Tropical disturbance: A tropical disturbance is a weather system characterized by a cluster of thunderstorms that produces organized convection but lacks a defined surface circulation. It is the initial stage of development for tropical cyclones and hurricanes, representing the early formation of a potential storm system. Tropical disturbances can lead to further intensification into tropical depressions, tropical storms, and eventually hurricanes if the right atmospheric conditions are present.
Tropical Storm: A tropical storm is a weather system characterized by strong winds and heavy rainfall that forms over warm ocean waters, typically between 23.5° latitude north and south of the equator. This system features organized thunderstorms and sustained winds ranging from 39 to 73 miles per hour. Tropical storms can intensify into hurricanes if conditions are favorable, making them a significant part of the broader category of tropical cyclones.
Typhoon: A typhoon is a powerful tropical cyclone that occurs in the Northwest Pacific region, characterized by strong winds, heavy rainfall, and a defined center of low pressure. Typhoons are essentially the same meteorological phenomena as hurricanes and cyclones but are given different names based on their location. They can cause significant damage to coastal areas through storm surges, flooding, and destructive winds.
Typhoon Haiyan: Typhoon Haiyan, known as Yolanda in the Philippines, was one of the strongest tropical cyclones ever recorded, striking the Philippines in November 2013. With sustained winds exceeding 195 mph and catastrophic storm surges, it caused widespread devastation, particularly in the Visayas region, and highlighted the vulnerability of coastal communities to extreme weather events.
Wind Shear: Wind shear refers to the change in wind speed and direction with height in the atmosphere. It plays a crucial role in the development and intensification of severe weather phenomena, including tornadoes and tropical cyclones. In severe thunderstorms, wind shear can enhance rotation, which is vital for tornado formation, while in tropical cyclones, it can either aid in their strengthening or lead to their weakening depending on its orientation relative to the storm system.