1 HURRICANES AND TORNADOES The most severe weather systems are hurricanes and tornadoes. They occur in extremely low pressure systems, or cyclones, when the air spirals rapidly into the center of a low. High winds and heavy rains can result in widespread floods, frequently bringing tremendous damage and many deaths in their wake. A hurricane is a large cyclone that develops over the oceans in the tropical regions. It can range from 100 miles to 1,000 miles in diameter, with winds as high as 300 miles per hour. In a hurricane, thick, water filled thunderstorm clouds form a circular spiral structure. The closer the clouds are to the center of the low-pressure system, the stronger the wind and the heavier the rainfall. Surprisingly, the very center of the low-pressure system-- called the eye of the hurricane-- is a place of relative calm. It contains few, if any, clouds. Sometimes the sun is even shining. This pleasant condition, however, is deceptive because high winds and tremendous rains at the edge of the hurricane s eye are ravaging the earth s surface. The hurricane season in the United States occurs during the months of June through November. Most Atlantic Ocean hurricanes get started as a low pressure system in the tropics off the west coast of Africa. Warm water and moisture laden air supply the energy (latent heat of condensation) for it to strengthen into an ordinary, average tropical storm. Most tropical storms encounter upper level winds moving in the opposite direction from the surface winds. As a result, these storms weaken and soon die out. On occasion the upper level winds support the development of the storm and a hurricane can be created. On average, we experience six hurricanes a year. When the storm reaches our shores, it often turns northward, and follows the coastline, causing widespread flooding of coastal areas. Tornadoes are very different from hurricanes, although they are still a type of cyclone. They do not travel far, they do not last long, and they are relatively small, usually varying in size from 100 feet to 1 mile in diameter. They occur most frequently in the warmer days of spring and summer, when the air is very moist. Normally, tornadoes form when air is forced to rise very rapidly. A tornadoes most distinctive feature is the peculiar funnel-shaped cloud that extends downward from the heavy cloud masses. The very low pressure inside the funnel of the tornado is a major cause of the damage done when the funnel touches earth. Traveling along the ground at miles/hour., the tornado can swoop people and property up in its funnel, carry them for a distance, and then drop them when its force decreases. The National Weather Service is responsible for warning us about approaching hurricanes and tornadoes. Contact your local National Weather Service office for information on what to do when such severe weather conditions threaten. Action should be taken to protect yourself and your property as soon as you learn that a hurricane or tornado may be on its way to your home town.
2 Hurricane conditions are reported to the National Weather Service by airplanes, weather balloons, ground radar stations, and weather satellites. Although hurricanes move slowly, it is difficult to predict their exact path because they can change direction very quickly. The National Weather Service issues a Hurricane Watch for a coastal area if it looks as if a hurricane may be striking within hours or less. A Hurricane Warning is issued when a hurricane appears to be headed toward a specific area and is expected to hit the area in 24 hours or less. Tornadoes are erratic in behavior and are even more difficult to predict than hurricanes. They develop over land areas under certain combinations of atmospheric conditions, for example, low pressure, high temperature, and high humidity. In the United States, tornadoes typically develop over the mid western states where three air masses can converge: a cool air mass moving down from Canada, a dry air mass flowing off the Rocky Mountains into the Great Plains area, and a warm, moist air mass moving up from the Gulf of Mexico. A Tornado Watch means that weather patterns could result in a tornado or severe thunderstorm. A Tornado Warning means that severe thunderstorms or tornadoes have been reported to the National Weather Service by radar stations, people trained to be spotters, and other reliable sources, including someone like yourself. You can help alert people to an impending tornado. If you see any funnel-shaped clouds, report them immediately to the National Weather Service office nearest you.
3 Focus: Hurricane tracking ACTIVITY 1 ON THE RIGHT TRACK Task: Students plot the progress of a hurricane on a tracking map and use longitude and latitude coordinates to track the hurricane, predict the storm s path, and issue warnings. Supplies: Hurricane tracking map, pencil, ruler, scrap paper, washer Procedure: A hurricane has been spotted in the Atlantic Ocean. Every 12 hours, between 7:00 am and 7:00 pm, you will receive information on the location of the eye of the hurricane and be asked to give the proper warnings to the areas that may be affected. You must issue a hurricane warning at least 12 hours before the hurricane hits so that the people have time to evacuate the area. Remember, however, that it is dangerous to evacuate an area at night; too many accidents can occur, and people panic. Each time you get the location of the hurricane eye, plot its position on the map. The hurricane, however is much larger then its eye. Therefore, use the washer to represent the area affected by the hurricane. That entire area will experience strong winds and heavy rains. Data and Questions: Put the answers on the answer sheet. 7:00 pm, May 1- hurricane is centered at 25 N and 62 W 1. Give the new hurricane a name. 2. Will you issue any warnings at this time? Why or why not? 7:00 am, May 2- hurricane is centered at 23 N and 67 W 3. What direction is the hurricane heading? 4. How many degrees of latitude and longitude has it traveled in the past 12 hours? 5. You can assume it will continue traveling at the same speed. Where will it be in the next 12 hours? Will you issue any warnings? For what areas? 7:00 pm, May 2- hurricane is centered at 26 N and 71 W 6. In what direction is the storm moving now? 7. Should you give warnings now to the people in any areas? 8. Has the hurricane s speed remained the same? 7:00 am, May 3- hurricane is centered at 27 N and 76 W 9. Should you give any warnings now 10. What areas will be affected? 11. Can you wait 12 hours to give out the warnings? Why? 7:00 pm, May 3- hurricane is centered at 28 N and 80 W 12. In what direction do you think the hurricane will continue? 13. Should you give out any new warnings? 7:00 am, May 4- hurricane is centered at 32 N and 81 W 14 What direction did the hurricane go? 15. Were the people in the affected areas warned in time to get out? 16. Who will receive your next warning? 7:00 pm, May 4- hurricane is centered at 35 N and 77 W 17. Was your warning correct? 18. What additional information would have helped you make more accurate predictions?
4 Focus: High risk tornado areas. ACTIVITY 2 THE ANSWER LIES IN THE NUMBERS Task: Students will analyze the frequency of tornadoes in the continental United States and determine the high risk areas. Supplies: tornado frequency map, colored pencils Procedure: Examine the tornado map. The numbers show how many tornadoes were reported in each state over a 25-year period. Make a key on your map to represent four risk zones. Zone 1 = less than 100 tornadoes Zone 2 = tornadoes Zone 3 = tornadoes Zone 4 = over 900 tornadoes Use a colored pencil and color all the states that have had 900 or more tornadoes. these are high risk areas. Use a second color to shade in all the states with 500 to 900 tornadoes. Use a third color to shade in all the states with 100 to 500 tornadoes. Use a forth color to shade in all the states with less than 100 tornadoes. Questions: Put the answers on the answer sheet. 1. What four states had the highest number of tornadoes? 2. Where are most of these states located? 3. What is the topography like in this area of the USA? 4. Give one reason why the number of tornadoes is so high in this area. 5. If you lived in Texas, what would you do to be prepared for a sudden tornado? 6. What state had the fewest number of reported tornadoes? 7. Why do states like Nevada, Utah, and Idaho have such low numbers of tornadoes? What is the topography like in those states?
5 Focus: Plot the Tri-State Tornado. ACTIVITY 3 THE TRI-STATE TORNADO Task: Students plot the path of a tornado and identify the damage that occurred along its path. Supplies: Map of the Tri-State Tornado, the table of the tornado s time sequence, and a ruler. Procedure: One tornado which occurred on March 18, 1925 ranks as the worst tornado disaster in the United States. The tornado struck in the afternoon, lasted for 3.5 hours and covered nearly 220 miles. The strong winds destroyed many towns and cities in Missouri, Illinois, and Indiana. There were 695 people killed, the greatest loss of life foe a tornado ever recorded. Another 2,000 were injured. The total damage was estimated at almost 50 million dollars. The map shows the path of the tornado. Using the table listing the tornado s time sequence, plot each town on the map along the path of the tornado. Next to your plot point: indicate the name of the town, the time that town was hit, the distance it traveled from Ellington, and the amount of damage (in percent). Use the map scale to determine where each town belongs on the line. The town of Ellington has been located and done for you. Use Ellington as an example to complete the map. TIME SEQUENCE OF THE TORNADO TIME TOWN DISTANCE (miles) DESTRUCTION (%) 1:01 pm Ellington :05 pm Redford :15 pm Annapolis :00 pm Biehle 65 80** 2:26 pm Gorham :34 pm Murphysboro :38 pm Desoto :44 pm West Frankfort :50 pm Parrish :00 pm Griffin :10 pm Owensville :18 pm Princeton ** double-funnel tornado Questions: Put the answers on the answer sheet. 1. Which two towns were completely destroyed by the tornado? 2. How long did it take the tornado to travel from Ellington to Biehle? 3. How many miles are between Ellington and Biehle? 4. How fast did the tornado travel between Ellington and Biehle? To determine speed use the following formula: number of miles number of minutes X 60 = the speed in miles per hour 5. What was the average speed of the tornado? To determine average speed use the following formula: total number of miles total number of minutes X 60 = the speed in miles per hour 6. Why do you think Owensville and Princeton suffered less damage than most other towns? 7. Between the towns of Gorham and Parrish, nearly 540 people were killed and another 1,400 were injured; it was the worst part of the tornado. How long did it take for this catastrophe to happen? 8. What could be done in the future to prevent such disasters?