Wind shear can be a tropical storm's best friend or worst enemy
It's a term frequently mentioned by meteorologists, but the phenomenon can have radically different effects depending on the type of storm it influences.
By
Jessica Storm, AccuWeather Meteorologist &
Jesse Ferrell, AccuWeather meteorologist and senior weather editor
Updated Aug 2, 2024 12:02 PM EDT
Wind shear is one of the many important factors that either makes or breaks a tropical storm during hurricane season. But what is it and how does it affect a tropical storm? Let’s find out.
One of the staple terms meteorologists mention frequently when discussing the possibility for tropical development is wind shear. But what is wind shear? And what does it have to do with tropical cyclones and other weather patterns?
Simply put, wind shear is the change in direction and speed of winds throughout the various levels of the atmosphere.
Understanding how wind shear influences weather patterns is somewhat complex as there are multiple types of wind shear and because it can be a factor over the ocean as well as over land.
When issuing forecasts for the tropical Atlantic, forecasters typically examine vertical wind shear, which is the change in winds at increasing heights in the atmosphere. Generally, strong vertical wind shear is bad news for tropical storms and hurricanes.
"Vertical wind shear is the most influential factor as far as tropical cyclones are concerned," AccuWeather Senior Meteorologist Alex Sosnowski said.
Tropical systems and hurricanes grow by becoming vertically stacked. "It can be helpful to visualize a stack of pancakes," AccuWeather Lead Hurricane Expert Alex DaSilva explained. When winds vary in speed and direction at the bottom of the atmosphere compared to higher levels of the atmosphere, the top of a tropical system can be pushed and tilted away from its base, causing it to become lopsided. If a mature hurricane is in place, it may weaken but will not necessarily dissipate.
"A tall, neat stack is what a tropical system wants to be, but wind shear can cause some pancakes to be displaced and the stack could fall over," said DaSilva.
Weaker tropical storms tilted in this manner can create openings in the thunderstorms surrounding a tropical storm's eye, which allow dry air to enter the storm or disrupt the flow of warm and moist air. Tropical systems thrive on warmth and moisture, so storms experiencing this can struggle and organize or even perish.
"Strong wind shear can occur when the jet stream extends over tropical waters and creates a zone of rapidly increasing wind speed at progressively higher levels of the atmosphere," said Sosnowski. A jet stream is like a high-speed atmospheric highway located at the level where passenger jets cruise and winds often reach speeds of 250 mph. The jet stream can also be very influential in tropical development, or the lack thereof.
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Horizontal wind shear is similar to its vertical counterpart but oriented in the opposite way as its name suggests. In relation to the tropics, horizontal wind shear is the change in horizontal winds over the surface of the ocean.
When a storm encounters this type of shear, the winds can drag or tear it apart. Horizontal wind shear can often produce powerful wind gusts that carry a tropical storm away from its current direction or disrupt the circular flow of the tropical system.
It's a rare occurrence, but wind shear can sometimes help tropical cyclones strengthen. One way this can happen is when horizontal wind shear pushes a storm over warmer waters, which are more conducive to tropical development. Another way it can contribute to strengthening is that increasing winds moving in the same direction as the system's circulation can cause the storm to spin faster and strengthen like a hand spinning a top.
Vertical wind shear is also an influential factor over land in the development of severe weather like damaging thunderstorms and tornadoes. If wind shear becomes strong enough, it can tilt a severe storm, much like it can do to a tropical storm. But, rather than weaken the storm or change the storm's course, this type of wind shear actually helps severe thunderstorm development by encouraging airflow outward at the top of the storm, and by keeping the updraft and downdraft away from each other, powering the storm.
"Severe thunderstorms need wind shear to grow and thrive," said DaSilva. A strong mid-level jet stream with weaker surface winds can even enhance a storm's rotation, increasing the risk of tornado development.
Every thunderstorm has a column of rising air, known as an updraft. The stronger the updraft is, the more intense the storm will become.
For a tornado to develop, air needs to rotate horizontally near the ground first. This rotation is caused by wind shear. When this rotating air is drawn into the updraft, it becomes tilted vertically.
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News / Hurricane
Wind shear can be a tropical storm's best friend or worst enemy
It's a term frequently mentioned by meteorologists, but the phenomenon can have radically different effects depending on the type of storm it influences.
By Jessica Storm, AccuWeather Meteorologist & Jesse Ferrell, AccuWeather meteorologist and senior weather editor
Updated Aug 2, 2024 12:02 PM EDT
Wind shear is one of the many important factors that either makes or breaks a tropical storm during hurricane season. But what is it and how does it affect a tropical storm? Let’s find out.
One of the staple terms meteorologists mention frequently when discussing the possibility for tropical development is wind shear. But what is wind shear? And what does it have to do with tropical cyclones and other weather patterns?
Simply put, wind shear is the change in direction and speed of winds throughout the various levels of the atmosphere.
Understanding how wind shear influences weather patterns is somewhat complex as there are multiple types of wind shear and because it can be a factor over the ocean as well as over land.
Wind shear in tropical storms
When issuing forecasts for the tropical Atlantic, forecasters typically examine vertical wind shear, which is the change in winds at increasing heights in the atmosphere. Generally, strong vertical wind shear is bad news for tropical storms and hurricanes.
"Vertical wind shear is the most influential factor as far as tropical cyclones are concerned," AccuWeather Senior Meteorologist Alex Sosnowski said.
Tropical systems and hurricanes grow by becoming vertically stacked. "It can be helpful to visualize a stack of pancakes," AccuWeather Lead Hurricane Expert Alex DaSilva explained. When winds vary in speed and direction at the bottom of the atmosphere compared to higher levels of the atmosphere, the top of a tropical system can be pushed and tilted away from its base, causing it to become lopsided. If a mature hurricane is in place, it may weaken but will not necessarily dissipate.
"A tall, neat stack is what a tropical system wants to be, but wind shear can cause some pancakes to be displaced and the stack could fall over," said DaSilva.
Weaker tropical storms tilted in this manner can create openings in the thunderstorms surrounding a tropical storm's eye, which allow dry air to enter the storm or disrupt the flow of warm and moist air. Tropical systems thrive on warmth and moisture, so storms experiencing this can struggle and organize or even perish.
"Strong wind shear can occur when the jet stream extends over tropical waters and creates a zone of rapidly increasing wind speed at progressively higher levels of the atmosphere," said Sosnowski. A jet stream is like a high-speed atmospheric highway located at the level where passenger jets cruise and winds often reach speeds of 250 mph. The jet stream can also be very influential in tropical development, or the lack thereof.
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Horizontal wind shear is similar to its vertical counterpart but oriented in the opposite way as its name suggests. In relation to the tropics, horizontal wind shear is the change in horizontal winds over the surface of the ocean.
When a storm encounters this type of shear, the winds can drag or tear it apart. Horizontal wind shear can often produce powerful wind gusts that carry a tropical storm away from its current direction or disrupt the circular flow of the tropical system.
It's a rare occurrence, but wind shear can sometimes help tropical cyclones strengthen. One way this can happen is when horizontal wind shear pushes a storm over warmer waters, which are more conducive to tropical development. Another way it can contribute to strengthening is that increasing winds moving in the same direction as the system's circulation can cause the storm to spin faster and strengthen like a hand spinning a top.
Wind shear in thunderstorms
Vertical wind shear is also an influential factor over land in the development of severe weather like damaging thunderstorms and tornadoes. If wind shear becomes strong enough, it can tilt a severe storm, much like it can do to a tropical storm. But, rather than weaken the storm or change the storm's course, this type of wind shear actually helps severe thunderstorm development by encouraging airflow outward at the top of the storm, and by keeping the updraft and downdraft away from each other, powering the storm.
"Severe thunderstorms need wind shear to grow and thrive," said DaSilva. A strong mid-level jet stream with weaker surface winds can even enhance a storm's rotation, increasing the risk of tornado development.
Every thunderstorm has a column of rising air, known as an updraft. The stronger the updraft is, the more intense the storm will become.
For a tornado to develop, air needs to rotate horizontally near the ground first. This rotation is caused by wind shear. When this rotating air is drawn into the updraft, it becomes tilted vertically.
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