Student Research

How do Hurricanes Work?

  • How do Hurricanes Form?
  • What does a Hurricane Look Like?
  • Where do Hurricanes Come From and Where do They Go?
  • How do Hurricanes Die?

Courtesy of Environment Canada, http://www.ns.ec.gc.ca/weather/hurricane/kids.html

Hurricanes are very large and powerful storms. They can bring heavy winds, rain and flooding to a region. Scientists are studying how these storms form, how they work and where they go so that we can be better prepared when a hurricane hits.

How do Hurricanes Form?

One of the most important ways of understanding hurricanes is understanding how they form. If scientists can figure out why hurricanes form in some conditions and not in others, then they can better predict when and where they will form.

There are several things that must be together for a hurricane to form:

  1. Hurricanes only form over really warm ocean water of 26.5° C or more. That's warm! Ocean water in the Maritimes never reaches this temperature so hurricanes cannot form in these waters.
  2. The atmosphere (the air) must cool off very quickly the higher you go. Have you ever noticed that it gets really cold when you climb to the top of a mountain? Same idea.
  3. The wind must be blowing in the same direction and at the same speed from the ocean surface right up to 9,000 metres above sea level.
  4. A hurricane will not form any closer than 500 kilometres to the equator. The Coriolis Force is needed to create the spin in the hurricane and it becomes too weak near the equator.

What Is The Coriolis Force?

The Coriolis Force is a force that deflects moving objects to one side because of the Earth's rotation. The object is still going straight but the Earth moves underneath it, making it look like it is moving to one side. In the Northern Hemisphere, the Coriolis Force deflects objects to the right.

Have you ever tried rolling a ball to a friend across the floor of a spinning merry-go-round? The ball looks like it is deflected to one side because of the spinning merry-go-round. This is the same idea as the Coriolis Force. Try it out!

So what happens when all of these conditions are there?

Sometimes nothing. Sometimes a hurricane or tropical storm (a weaker form of storm) is formed. The warm ocean water warms the air above it. This air rises because it is lighter than the cooler air above. When the parcel of warm air reaches the cooler air above, the water vapor turns into water drops and warms the surrounding air. When the warm air rises, the cool air replaces it and wind is created. The wind will start spinning because of the Coriolis Force and a tropical storm or hurricane is formed!

What Does a Hurricane Look Like?

Hurricanes can be big or small. Some hurricanes can be as big as 1000 kilometres across (that's about the distance between Halifax and Quebec City), while others are only a few hundred kilometres across.

You might also have noticed that hurricanes spiral in a counter-clockwise direction. That's the Coriolis Force again.

Satellite Picture of a Hurricane

Hurricanes have a distinctive feature called an eye. The eye of a hurricane is in the middle of the spiral. The eye is produced by the spiraling action of the storm and it is the area where the air is slowing sinking. When the eye of a hurricane passes over a region the winds decrease to just a gentle breeze, and the rain stops. You may even be able to see the sun during the day or the stars at night. Then, the rest of the storm passes and the wind suddenly changes directions and becomes ferocious again. The eyewall is the area inside the hurricane where the winds and rain are the worst. The eyewall is the area surrounding the eye.

You can make your own "hurricane eye" at home! First, fill a bathtub with about 3 inches of water. Now pull the plug. You'll notice that the water spirals around the drain before it goes down. The spiraling water gets faster and faster, and when the water is shallow enough, you can look down the middle of the "eye," right into the drain. You might even be able to put your finger into the middle of the spiral without getting it wet. The fastest spinning water is right at the edge of the "eye" - that's like the eyewall. Further away from the eye, the water moves much slower.

Despite what you might read in some books, the direction of spinning water has nothing to do with the turning of the earth (like the Coriolis Force) - it's determined by the shape of the tub, the location of the drain, and how you pull out the plug.

Where do Hurricanes Come From and Where do They Go?

Hurricanes can only develop over really warm ocean water. See How do Hurricanes Form? So, no hurricanes are formed near Canada. You might have heard reports of hurricanes near us on the news though. What's the deal? Well, hurricanes form over warmer water but they can move around. Hurricanes can last for days or even weeks and move huge distances. The hurricanes and tropical storms that affect North America usually form in the eastern Atlantic Ocean where the water is very warm.

This map shows where hurricanes form (the purple) and the main tracks that they follow around the world (the black arrows).

The storms move across the ocean and often curve up the east coast of the continent and move toward us. Most hurricanes weaken before they reach us and a lot of them stay out over the open ocean away from land. Sometimes they reach us and bring lots of rain and high winds.

Types of Tropical Cyclones

There are three types of tropical cyclones:

Tropical depression - An organized system of clouds and thunderstorms with a well defined circulation and maximum sustained wind of 37 to 62 kilometres per hour (20 to 33 knots.)
Tropical storm - An organized system of strong thunderstorms with a well defined circulation and maximum sustained winds of 63 to 117 kilometres per hour (34 to 63 knots.) It is at this point that the storm is given a name.
Hurricane - An intense tropical weather system with a well defined circulation and maximum sustained winds of 118 kilometres per hour (64 knots) or higher. In the western Pacific, hurricanes are called "typhoons," and similar storms in the Indian Ocean are called "cyclones." At this stage, the storm has an "eye."

How do Hurricanes Die?

Hurricanes are kind of like people: they are born, they grow up, and they die. A hurricane will weaken and die when it reaches land. The hurricane no longer has its energy source (warm water) and it's just like a car without gas. A hurricane that travels over the colder waters of the north also weakens, but not as quickly. Most of the hurricanes that affect us are hurricanes that are in the process of weakening and dying.

To find out more about hurricanes near Canada go http://www.ns.ec.gc.ca/weather/hurricane/connection.html

YES I Can! Science

info@yesican-science.ca