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Unit 3: Hurricane Tracks and Energy

Lisa Gilbert (Williams College), Josh Galster (Montclair State University), Joan Ramage (Lehigh University)

Summary

The purpose of this unit is to learn some of the scientific tools used to determine hurricane location, path, and strength. Students plot the path of a recent hurricane (Irene, 2011), work with an online viewer to learn the typical tracks hurricanes follow, and use a measure of hurricane energy to compare individual hurricanes and yearly totals. In Activity 3.1, on a standard National Oceanic and Atmospheric Administration (NOAA) Atlantic Hurricane Map, students gain experience in plotting a hurricane track and in basic mapping skills. In Activity 3.2, students work with an online viewer to learn about the typical paths and landfall patterns of Atlantic hurricanes. Students compare the locations, paths, and variation of hurricane tracks from a century-scale record. In Activity 3.3, students use the Accumulated Cyclone Energy (ACE) index as a way of measuring hurricane season totals and consider the policy implications of a predicted above-normal hurricane year. Note: computer lab with Internet access (or student laptops in the lecture/lab room) required for Activity 3.2.

Learning Goals

After completing this unit students will be able to:
  • Plot hurricane position using latitude and longitude.
  • Describe the path and strength of Hurricane Irene (2011).
  • Describe the spatial variability of storm trajectories and speeds based on the historical record in the Atlantic Ocean.
  • Determine the recurrence interval of hurricanes for a particular location.
  • Calculate the energy associated with a hurricane season.
  • Compare seasonal ACE totals to distinguish above average from below average seasons.
  • Elaborate on why predictions of the current hurricane season are useful for society.

This unit relates to the following Earth Science Literacy Big Ideas:

  • Earth's atmosphere changes over time and space, giving rise to weather and climate.
  • Students will learn that geoscientists address problems that cross disciplinary boundaries.
  • Earth scientists use repeatable observations and testable ideas to understand and explain our planet.

Context for Use

After students have learned about hurricane characteristics, this unit will provide them with experience tracking hurricanes. This unit may be used with the Natural Hazards and Risks: Hurricanes module, or as a stand-alone unit. The unit may be used in any course discussing natural hazards, or can be modified to fit a variety of earth, atmospheric, and marine science courses. The unit is appropriate for introductory-level college students or as the basis for more in-depth class exploration of hurricane paths for upper-level students.

Activity 3.1 involves basic map skills and could be used as a homework or lab exercise or skipped for intermediate courses; it is not required for completing the remainder of the unit. Activity 3.2 is an in-class (or lab) demonstration or interactive exercise. For all students to be engaged in Activity 3.2, Internet access is required for every student or every pair of students (and laptops, tablets, or a computer room). Activity 3.3 includes an in-class (or lab) lecture and activity, but could be used for homework if time is limited.

Description and Teaching Materials

Activity 3.1

Using the data from Hurricane Irene (2011), students will plot latitude and longitude positions of a specific storm and think about changes in direction, speed, and strength of the storm over time. Note that this activity is fairly basic and if your students are more advanced, you can skip Activity 3.1 and start with Activity 3.2.

Instruct students to plot noon positions of Hurricane Irene's (2011) track. Use the NOAA gridded map of Atlantic basin (Acrobat (PDF) 1.9MB Jun17 12) and the Tables of 6-hourly hurricane Positions and Saffir-Simpson Scale (Acrobat (PDF) 83kB Oct23 12). Use the maximum sustained wind speed and the Saffir-Simpson Table that is included with the hurricane positions to determine the category of hurricane for each position, and label it on the map. Optional: Change color scale or line thickness according to storm category.

Ask students: How fast did the storm move on different days? What was the maximum strength (category) of the storm on the Saffir-Simpson scale? When and where did it make landfall in the United States? [Think about (more on this later) how the factors combined to make this storm devastating, even though it was not among the highest category storms.]

Activity 3.2

Use the Historical Hurricane Tracks website from NOAA to interpret storm frequency from 1842 to about two years ago. This activity requires Internet access and computers for the students.

How it works: A PowerPoint file is provided Hurricane Tracker intro and questions (PowerPoint 2007 (.pptx) 1.5MB Sep9 15) with screenshots of the activity and questions that you can use to introduce students to the main features. Introduce the question: How does storm strength and frequency change with decade and region?

For a more intermediate to advanced class, comfortable with plotting and visualizations, students can proceed directly to examining the details of Sandy's (2012) track while also learning the functions of the hurricane tracker.

Instructions: Load http://coast.noaa.gov/hurricanes/ and have students type in Sandy 2012 in the "Name/Year" window to explore the functions of the Hurricane Tracker. Have them work with a partner to answer the following questions:

  1. Positions are ___ hours apart.
  2. What is the Hurricane Category on the Saffir-Simpson scale? When and where?
  3. When and where was landfall in the United States? What was the wind speed?
  4. Where and when was the hurricane moving the fastest?
  5. Other interesting observations? Are there things you did not expect?

(Discuss answers with class; they are shown below under assessments.)

Then, ask students answer the following questions about the history of hurricanes in the area by typing their zip code in the "Location" window the hurricane tracker:
  1. How many hurricanes made landfall within 60 nautical miles of our zip code between 1851 and 2010?
  2. What is the recurrence interval (average time between hurricanes) here?
  3. What is the recurrence interval of major hurricanes here?

Answer Key:

Additional Questions (optional, if time permits)

  • (If Activity 3.1 was done) How does the storm you plotted by hand (Irene) compare to the historical record in terms of the track, speed of the hurricane, wind speed, and area where it made landfall in the United States? For example, how many storms recorded since 1851 made landfall in the United States about where Irene did? What time of year were these storms? How did they compare in strength to Irene?
  • Now that you have some experience looking at past hurricanes, look up the NHC Tropical Cyclone Activity to see if any are affecting the United States now. Describe the recent or ongoing hurricane patterns (this question is a bit seasonal: June through November most years).

Activity 3.3

Present slides in the PowerPoint file (PowerPoint 2007 (.pptx) 1.5MB Aug25 14), introducing hurricane seasonal outlooks, the Saffir-Simpson scale, and the Accumulated Cyclone Energy index. You can modify the PowerPoint to include data from a different hurricane or a different season archived here: http://rammb.cira.colostate.edu/products/tc_realtime/.

Distribute the Student handout (Microsoft Word 229kB Aug25 14) and review, as needed:

  • Calculating the ACE index:
  1. When storm is at least tropical storm strength, every six hours find the maximum wind speed in knots. (You will have four each day: 0000-0600, 0600-1200, 1200-1800, 1800-2400.)
  2. Square the maximum wind speed for each six-hour period. (Now your units are kt2).
  3. Add the sum of the squares.
  4. Divide by 104 kt2. (Now ACE is a unitless index. Small hurricanes might have an ACE near 1, larger hurricanes might have ACE around 20 or even higher.)
  • To calculate seasonal ACE index, sum all the storm ACE indices for a single season.

An above-normal season is one with a total ACE >111. A below-normal year is one with a total ACE <71.

Additional thought questions for summer or fall classes:
  • Open the most recent hurricane season outlook for the Atlantic Ocean. What are the implications for this outlook (above-normal, normal, or below-normal) for a farmers' collective in Georgia? For a governor in New Jersey? A fisherman in Louisiana? For you?


Teaching Notes and Tips

Activity 3.1

Options:

  1. To simplify and shorten, plot data once per day. Note that the 0000Z position (midnight Zulu, also known as UTC or GMT) is 7:00 p.m. EST during Irene (2011);
  2. Alternatively, for a detailed view students could plot all positions.

For further exploration, the activity could be modified for a more recent or regionally relevant hurricane using historical hurricane tracker at the National Hurricane Center.

Activity 3.2

For a more intermediate to advanced class comfortable with plotting and visualizations, students can proceed directly to examining the details of Sandy's track while also learning the functions of the hurricane tracker.

Questions to guide student exploration are listed above (with answers below under assessment). In addition, ask students to reflect, using the hurricane tracker:
  1. Have there been more or fewer hurricanes here in your own lifetime than you would have expected?
  2. Were you initially surprised at the path Sandy took? Do you think you would have been surprised by Sandy's path if you had seen the paths of other October hurricanes first (in other words, if you had more of the data geoscientists have)?

Answer Key:

Activity 3.3

This activity could be modified for another year using Seasonal Climate Summary data from the National Hurricane Center.

Assessment

Activity 3.1

The expected outcome is for students to produce a map with the trajectory of Hurricane Irene. Students should be assessed on whether the points are correctly located and labeled (and if assigned, whether the line color or thickness represents the speed). Maps should be clear, reasonably accurate, and complete.

Students can self-assess by comparing their map with another resource such as http://www.noaa.gov/extreme2011/irene.html

Activity 3.2

Instructions: Load http://coast.noaa.gov/hurricanes/ and have students type in Sandy 2012 in the "Name/Year" window to explore the functions of the hurricane tracker. Have them work with a partner to answer the following questions:

  1. Positions are ___ hours apart.
  2. What is the Hurricane Category on the Saffir-Simpson scale? When and where?
  3. When and where was landfall in the United States? What was the wind speed?
  4. Where and when was the hurricane moving the fastest?
  5. Other interesting observations? Are there things you did not expect?

Discuss answers with class.

Then, ask students answer the following questions about the history of hurricanes in the area by typing their zip code in the "Location" window the hurricane tracker:
  1. How many hurricanes made landfall within 60 nautical miles of our zip code between 1851 and 2010?
  2. What is the recurrence interval (average time between hurricanes) here?
  3. What is the recurrence interval of major hurricanes here?

Answer Key:


Activity 3.3

The "comparing years" questions are embedded assessments. Using the ACE data (Excel 2007 (.xlsx) 45kB Aug6 12) table or a plot of the data, students will make lists of:

1. Which years were above normal?

  • Years with ACE>111

2. Which years were below normal?

  • Years with ACE<71

Next, students will plot time on the x axis and ACE on the y axis. Have them analyze the data visually, assuming there is a 25-year cycle of above and below normal phases, to determine:

3. Which phase are we in now (above or below normal)? When did this phase start, and when will it likely end? Does this surprise you given what you have heard about hurricanes and climate in the news?

  • The high activity era began in 1994 and will likely last until about 2019.
  • Students may have heard that warmer tropical waters may lead to more large hurricanes in the future, and should reflect on the difference between a trend and a multi-decadal oscillation.

Additional thought questions for summer or fall classes:

  • Open the most recent hurricane season outlook for the Atlantic Ocean. What are the implications for this outlook (above-normal, normal, or below-normal) for a farmers' collective in Georgia? For a governor in New Jersey? A fisherman in Louisiana? For you?

References and Resources

Additional resources:

Data sources:

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These materials are part of a collection of classroom-tested modules and courses developed by InTeGrate. The materials engage students in understanding the earth system as it intertwines with key societal issues. The collection is freely available and ready to be adapted by undergraduate educators across a range of courses including: general education or majors courses in Earth-focused disciplines such as geoscience or environmental science, social science, engineering, and other sciences, as well as courses for interdisciplinary programs.
Explore the Collection »