How To Be An Expert…On Hurricanes…Mastering The Fundamentals

It was July of 1961 and the 38 members of the Green Bay Packers football team were gathered together for the first day of training camp with famed coach Vince Lombardi. They had just come off a heartbreaking defeat against the Philadelphia Eagles in the NFL Championship – a loss which the Packers took very hard. Lombardi took nothing for granted so addressing his experienced time, he began with the most famopus and elemental statement of all. “Gentlemen,” he said, holding a pigskin in his right hand, “this is a football.”

So with the fundamentals in mind, we wanted to review exactly what a Hurricanes is, and what the terms mean, and the categories clearly spelled out. So we went to NASA for the basics.

From NASA: Hurricanes are large, swirling storms. They produce winds of 119 kilometers per hour (74 mph) or higher. That’s faster than a cheetah, the fastest animal on land. Winds from a hurricane can damage buildings and trees.

Hurricanes are the most violent storms on Earth. People call these storms by other names, such as typhoons or cyclones, depending on where they occur. The scientific term for all these storms is tropical cyclone. Only tropical cyclones that form over the Atlantic Ocean or the eastern Pacific Ocean are called “hurricanes.”

Whatever they are called, tropical cyclones all form the same way.

Hurricanes form over warm ocean waters. Sometimes they strike land. When a hurricane reaches land, it pushes a wall of ocean water ashore. This wall of water is called a storm surge. Heavy rain and storm surge from a hurricane can cause flooding.

World map showing area where cyclones occur.

 

Tropical cyclones are like giant engines that use warm, moist air as fuel. That is why they form only over warm ocean waters near the equator. The warm, moist air over the ocean rises upward from near the surface. Because this air moves up and away from the surface, there is less air left near the surface. Another way to say the same thing is that the warm air rises, causing an area of lower air pressure below.

A cumulonimbus cloud. A tropical cyclone has so many of these, they form huge, circular bands.

Air from surrounding areas with higher air pressure pushes into the low-pressure area. Then that “new” air becomes warm and moist and rises, too. As the warm air continues to rise, the surrounding air swirls in to take its place. As the warmed, moist air rises and cools off, the water in the air forms clouds. The whole system of clouds and wind spins and grows, fed by the ocean’s heat and water evaporating from the surface.

Storms that form north of the equator spin counterclockwise. Storms south of the equator spin clockwise. This difference is because of Earth’s rotation on its axis.

As the storm system rotates faster and faster, an eye forms in the center. It is very calm and clear in the eye, with very low air pressure. Higher pressure air from above flows down into the eye.

Tropical cyclone cross-section

If you could slice into a tropical cyclone, it would look something like this. The small red arrows show warm, moist air rising from the ocean’s surface, and forming clouds in bands around the eye. The blue arrows show how cool, dry air sinks in the eye and between the bands of clouds. The large red arrows show the rotation of the rising bands of clouds.


When the winds in the rotating storm reach 39 mph, the storm is called a “tropical storm.” And when the wind speeds reach 74 mph, the storm is officially a “tropical cyclone,” or hurricane.

Tropical cyclones usually weaken when they hit land because they are no longer being “fed” by the energy from the warm ocean waters. However, they often move far inland, dumping many inches of rain and causing lots of wind damage before they die out completely.

Once a hurricane forms, weather forecasters predict its path. They also predict how strong it will get. This information helps people get ready for the storm.

There are five types, or categories, of hurricanes. The scale of categories is called the Saffir-Simpson Hurricane Scale. The categories are based on wind speed.

  • Category 1: Winds 119-153 km/hr (74-95 mph) – faster than a cheetah
  • Category 2: Winds 154-177 km/hr (96-110 mph) – as fast or faster than a baseball pitcher’s fastball
  • Category 3: Winds 178-208 km/hr (111-129 mph) – similar, or close, to the serving speed of many professional tennis players
  • Category 4: Winds 209-251 km/hr (130-156 mph) – faster than the world’s fastest rollercoaster
  • Category 5: Winds more than 252 km/hr (157 mph) – similar, or close, to the speed of some high-speed trains

What Are the Parts of a Hurricane?

  • Eye: The eye is the “hole” at the center of the storm. Winds are light in this area. Skies are partly cloudy, and sometimes even clear.
  • Eye wall: The eye wall is a ring of thunderstorms. These storms swirl around the eye. The wall is where winds are strongest and rain is heaviest.
  • Rain bands: Bands of clouds and rain go far out from a hurricane’s eye wall. These bands stretch for hundreds of miles. They contain thunderstorms and sometimes tornadoes.

How Does a Storm Become a Hurricane?
A hurricane starts out as a tropical disturbance. This is an area over warm ocean waters where rain clouds are building.

A tropical disturbance sometimes grows into a tropical depression. This is an area of rotating thunderstorms with winds of 62 km/hr (38 mph) or less.

A tropical depression becomes a tropical storm if its winds reach 63 km/hr (39 mph).

A tropical storm becomes a hurricane if its winds reach 119 km/hr (74 mph).

What Makes Hurricanes Form?
Scientists don’t know exactly why or how a hurricane forms. But they do know that two main ingredients are needed.

One ingredient is warm water. Warm ocean waters provide the energy a storm needs to become a hurricane. Usually, the surface water temperature must be 26 degrees Celsius (79 degrees Fahrenheit) or higher for a hurricane to form.

The other ingredient is winds that don’t change much in speed or direction as they go up in the sky. Winds that change a lot with height can rip storms apart.

How Are Hurricanes Named?
There can be more than one hurricane at a time. This is one reason hurricanes are named. Names make it easier to keep track of and talk about storms.

A storm is given a name if it becomes a tropical storm. That name stays with the storm if it goes on to become a hurricane. (Tropical disturbances and depressions don’t have names.)

Each year, tropical storms are named in alphabetical order. The names come from a list of names for that year. There are six lists of names. Lists are reused every six years. If a storm does a lot of damage, its name is sometimes taken off the list. It is then replaced by a new name that starts with the same letter.

Last Updated: Aug. 4, 2017
Editor: Sandra May
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