Tropical cyclone

A tropical cyclone is a powerful storm system that forms over warm ocean waters. It has strong winds, heavy rain, and thunderstorms arranged in a spiral. Depending on where it happens and how strong it is, a tropical cyclone may be called a hurricane (/ˈhʌrɪkən, -keɪn/) in the Atlantic Ocean or northeastern Pacific Ocean, a typhoon (/taɪˈfuːn/) in the northwestern Pacific Ocean, or simply a tropical cyclone in the Indian Ocean and South Pacific.

These storms get their energy from the heat of the ocean. Warm water evaporates into the air, which then rises and cools, forming clouds and rain. This process gives the storm its power. Tropical cyclones usually form far from the equator because they need the Earth's rotation to spin.

When a tropical cyclone reaches the coast, it can cause damage with strong winds, heavy rain, big waves, and storm surges. While areas near the coast often face the most impact, heavy rain can cause flooding far inland. Scientists have noticed that climate change affects tropical cyclones, potentially making these storms stronger and more frequent as ocean waters get warmer.

Definition and terminology

A tropical cyclone is a large storm with strong winds and heavy rain that forms over warm ocean waters. It has a center with very low pressure and thunderstorms around it. When these storms have winds faster than 35 kilometers per hour, they are called tropical cyclones.

Depending on where they occur, these storms have different names. In the Atlantic Ocean or northeastern Pacific Ocean, they are called hurricanes. In the northwestern Pacific Ocean, they are called typhoons. In the Indian Ocean and South Pacific, they are usually called tropical cyclones. The word "tropical" tells us these storms start near the equator, and "cyclone" means their winds spin in a circle.

Formation

Main article: Tropical cyclogenesis

Tropical cyclones usually form during the summer but can appear almost any month in warm areas of the world. They often start near the Intertropical Convergence Zone, where warm air rises and creates thunderstorms. These thunderstorms can group together and begin to rotate, helped by the Earth's spin.

For a tropical cyclone to grow stronger, several conditions are needed: warm ocean water, low wind changes between heights, moist air, and enough turning force from the Earth. The ocean's temperature and other weather patterns like El Niño–Southern Oscillation can influence when and where these storms develop. Different parts of the world have special centers that watch for these storms and give warnings to keep people safe.

Interactions with climate

Every year, about 80 to 90 named tropical cyclones form around the world. Most of these storms happen in late summer when the difference between temperatures high up in the air and temperatures at the ocean surface is the greatest. Each ocean area has its own storm season. For example, the Atlantic Ocean has its most storms from June to November, with the peak in early September.

Climate change can affect tropical cyclones in several ways. Warmer ocean temperatures can give storms more energy, potentially making them stronger and increasing the amount of rain they bring. Scientists have observed that very intense storms, especially those rated Category 4 or 5, have become more common in recent years. Warmer air can also hold more moisture, which means storms can produce even heavier rainfall. Additionally, rising sea levels can make coastal flooding from storms worse. However, scientists are still studying exactly how climate change will affect the total number of storms that form each year. Some studies suggest there may be fewer storms overall, but those that do form could be more powerful and affect areas farther from the equator than before.

Intensity

Tropical cyclones get stronger or weaker based on their wind speeds and pressure. Scientists use tools like satellites and special airplanes to measure how strong these storms are. The strongest storm ever recorded was Typhoon Tip in 1979, with very low pressure and very fast winds.

Warm ocean water helps tropical cyclones grow. When the water is extra warm, storms can get stronger very quickly. But if the storm moves over cooler water or land, it can weaken. Scientists have many ways to measure a storm’s strength, including looking at satellite pictures and using special numbers to guess how powerful it is.

Classification and naming

Tropical cyclones are given different names depending on where they occur and how strong they are. In the Atlantic Ocean and northeastern Pacific, they are called hurricanes when their winds are very strong. In the western Pacific and Indian Ocean, they are called typhoons or severe cyclonic storms. Smaller or weaker storms might be called tropical storms, cyclonic storms, or tropical depressions.

These storms are given personal names to help people remember them and stay safe during warnings. Naming storms helps avoid confusion, especially when multiple storms occur at the same time. The names come from lists created by weather services around the world. If a storm is especially damaging, its name is retired and replaced with a new one.

Structure

Eye and center

Main article: Eye (cyclone)

At the center of a strong tropical cyclone, air sinks and creates a calm area called the "eye." This eye is usually clear of clouds and about 30 to 65 kilometers wide, though it can be smaller or much larger. Around the eye is the "eyewall," where the strongest winds and heaviest rain occur.

Size

Tropical cyclones come in many sizes. They can be as small as 100 kilometers across or as large as 2,000 kilometers. The largest ones are usually found in the northwest Pacific Ocean, while the smallest are in the northeastern Pacific Ocean. For example, Typhoon Tip was one of the largest ever recorded, with winds stretching over 2,170 kilometers in diameter.

Movement

The movement of a tropical cyclone, also known as its track, is mainly influenced by two things: steering by surrounding winds and beta drift. Steering happens when strong winds in the environment push the storm along, much like leaves carried by a stream. This is the main force guiding the storm's path.

Another factor is beta drift, where the storm slowly moves toward the poles and westward due to the Earth's rotation. This effect is stronger for bigger and more powerful storms. Sometimes, when two tropical cyclones come close, they can influence each other's movement, orbiting around a point between them. As a storm moves toward higher latitudes, it may also start to move poleward and eastward, a change known as recurvature.

Effects

Tropical cyclones can create big waves, heavy rain, and strong winds, which can disrupt ships far out at sea. On land, powerful winds can damage buildings, vehicles, and trees, sometimes turning loose objects into dangerous projectiles. The most serious effect is the storm surge, where the sea level rises dramatically, often causing the worst damage and many deaths.

These storms also bring other hazards like rip currents, tornadoes, and heavy rain that can cause flooding. They can bring needed rain to dry areas but can also worsen wildfires by fanning flames with their strong winds. The rain and wind can damage farms, homes, and infrastructure, leading to loss of property and sometimes lives. Flooding can lead to health issues and the spread of diseases.

Observation and forecasting

Observation

Tropical cyclones have existed worldwide for thousands of years. Scientists study old records and natural clues like sand deposits to learn about past storms. Before satellites, many storms went unnoticed unless they hit land or ships.

Today, we track storms using weather satellites that take pictures every 15 to 30 minutes. When a storm nears land, Doppler radar gives detailed updates every few minutes. Special airplanes, called hurricane hunters, fly into storms to measure wind and weather conditions directly.

Forecasting

See also: Tropical cyclone track forecasting, Tropical cyclone prediction model, and Tropical cyclone rainfall forecasting

Computers help scientists predict where storms will go by looking at air pressure and other factors. While we can guess a storm's path fairly well, it's still hard to know exactly how strong a storm will become. Forecasters update their predictions every six hours.

Geopotential height

Main article: Geopotential height

Scientists use something called geopotential height to understand air pressure and predict weather. They look at several levels high in the sky to see where moisture and movement might cause rain. The lowest level they watch is about 1,500 meters above sea level, and the highest they track is around 12,000 meters up.

Awareness and response

Before tropical cyclone seasons begin, people are encouraged to get ready. They think about their risks, check insurance, and gather emergency supplies. If a tropical cyclone is coming, weather offices issue warnings to help people stay safe.

After a hurricane, workers help clean up and fix things. They work with many groups to restore buildings, clear away waste, and repair roads. It’s important to work with trained groups for safety. Responders can face dangers like unsafe buildings and bad weather, so they need to stay careful and well-rested.

Extraterrestrial tropical cyclones

Limited research has explored whether tropical cyclones can form on planets beyond Earth. Large storm systems, such as Venus's north polar vortex and Saturn's Hexagon, have been observed, but these are different from Earth's tropical cyclones. On Titan, Saturn's largest moon, scientists have not found tropical cyclones, though its methane cycle creates weather similar to Earth's water cycle.

Studies suggest that tropical cyclones might exist on Earth-like planets orbiting stars far away. These planets could support such storms, especially if they have the right rotation speed and are close enough to their star to maintain liquid water.