On September 29, 2005, Hurricane Katrina swept into the Gulf Coast of the United States, causing enormous damage. The 2005 hurricane season was the worst ever recorded. What causes these storms? What can we learn about them to help us understand the forces found in weather? What should we do when a storm threatens?
How Hurricanes Form
The earth gets huge amounts of energy from the sun. This energy enters the earth’s atmosphere as light. As you know from having sunlight shine on your skin, light energy changes to heat energy when it shines on something.
The heat energy from the sun is strongest near the equator where sunbeams hit the earth at a 90-degree angle at mid day. The farther you are from the equator, the smaller the angle of sunlight hitting the earth at noon. Sunlight from a low angle is not as strong. This means that the oceans near the equator receive a lot more heat energy than anywhere else on earth.
Ask an adult if you can borrow a hair drier. Plug the hair drier in and use it to blow warm air into a plastic bag. Hold the bag with the open side towards the floor. Keep blowing air into the plastic bag until you have warmed the air inside it for a minute or two. Now let go. What happens to the plastic bag? Does it float up towards the ceiling?
The warm air near the equator does the same thing, it rises. Cooler air has to move in to fill the space left by the rising warm air. The air rushing in to replace the rising warm air becomes a powerful wind. Because the earth rotates or spins, this wind spirals in towards the center of the storm. The warm rising air carries huge amounts of moisture into the atmosphere, causing huge amounts of rain.
The warm, wet air of a tropical storm near the equator starts to move towards the cooler waters farther away from the equator. Once the speed of the winds in the storm reaches 73 miles an hour, the storm is called a hurricane.
NASA’s Windows on the Universe website explains a little more about hurricane formation and has some more diagrams to look at.
When a hurricane reaches land, the powerful winds and heavy rains can cause a lot of damage. Part of the damage comes from the storm surge. The winds moving towards the center of the hurricane and the very low air pressure at the center of the storm can mound water up. The ocean water at the center of a hurricane actually is higher than the surrounding ocean waters. When this big mound of water hits a coast, it can do a lot of flood damage, depending on the shape of the land.
Once a tropical storm reaches land, it starts to weaken. Without warm water, the storm loses energy. Wind speeds will decrease and the air mass loses moisture. Soon the hurricane goes back to being a tropical storm. As it weakens more and more, the storm may be called the tail end of a hurricane. These hurricane remnants sometimes reach New York State and still have enough rain and wind power to cause damage.
How do you prepare when a powerful storm is coming? If you are close to the coast and the storm is powerful, it may be best to leave the area and move inland or to higher ground. Homeowners in an area about to be hit by a hurricane will often put boards over windows to try to keep them from breaking from the wind and rain. Getting prepared is a good idea even far inland. This usually involves being ready if the electrical power goes off for very long. Having food, water, a flashlight and a battery-operated radio will help you during a large storm. See the American Red Cross site for more details on how to get prepared for storms.
There are some very good websites for you to learn more about hurricanes. The Science With NOAA website has a good basic science section on hurricanes for students.
Miami Museum of Science also has Hurricane Science resources.
The 53rd Weather Reconnaissance Squadron, Airforce Reserve is called the Hurricane Hunters. They fly into the eye of hurricanes to measure and track them. Their website has a virtual Cyberflight to explain their work.
The Weather Channel's Hurricane Central provides updated information about current storms.
FEMA, the Federal Emergency Management Agency has hurricane preparedness resources for students.