1. © 2012 Pearson Education, Inc. Lecture Presentation Chapter 10 Hurricanes and Extratropical Cyclones

2. © 2012 Pearson Education, Inc. Learning Objectives  Understand the weather conditions that create, maintain, and dissipate cyclones  Understand the difficulties in forecasting cyclone behavior  Know what geographic regions are at risk for hurricanes and extratropical cyclones  Understand the effects of cyclones in coastal and inland areas

3. © 2012 Pearson Education, Inc. Learning Objectives, cont.  Recognize linkages between cyclones and other natural hazards  Know the benefits derived from cyclones  Understand adjustments that can minimize damage and personal injury from coastal cyclones  Know the prudent actions to take for hurricane or extratropical cyclone watches and warnings

4. © 2012 Pearson Education, Inc. Introduction to Cyclones  An area or center of low pressure with rotating winds  Counter-clockwise in Northern Hemisphere  Clockwise in Southern Hemisphere  Tropical or extratropical  Based on origin and core temperature  Characterized by intensity  Sustained wind speeds and lowest atmospheric temperature

5. © 2012 Pearson Education, Inc. Tropical and Extratropical Cyclones  Tropical Cyclones  Form over warm tropical or subtropical ocean water (5°–20°)  Have warm central cores  Tropical depressions, tropical storms, hurricanes  High winds, heavy rain, surges, and tornadoes  Derive energy from warm ocean water and latent heat  Extratropical Cyclones  Form over land or water in temperate regions (30°–70°)  Associated with fronts and cool central cores  Strong windstorms, heavy rains, surges, snowstorms, blizzards  Most do not produce severe weather  Derive energy from temperature contrasts along fronts

6. © 2012 Pearson Education, Inc. Classification  Nor’easter  Extratropical cyclone that moves along northward along East Coast U.S.  Hurricanes  Tropical cyclones in Atlantic and eastern Pacific Oceans  Typhoons  Tropical cyclones in Pacific Ocean west of International Dateline and north of the equator  Cyclones  Tropical cyclones in Indian Ocean  Saffir-Simpson Scale classifies hurricanes based on wind speed

7. © 2012 Pearson Education, Inc. Table 10.1

8. © 2012 Pearson Education, Inc. Naming  Extratropical storms are sometimes named after their origins  Example: Alberta Clipper  Hurricanes named by international agreement through World Meteorological Organization  Named once winds exceed 63 km (39 mi.) per hour  Names assigned sequentially each year from list for each origin  Male/Female names alternated  Names are reused every 6 years  Names of big storms are retired (example: Katrina)

9. © 2012 Pearson Education, Inc. Cyclone Development: Tropical Disturbance  A organized mass of thunderstorms persisting for > 24 hours  Typically 200 to 600 km (120 to 370 mi.)  Has a weak rotation due to Coriolis effect  Formed by  Lines of convection  Upper-level low pressure troughs  Cold front remnants  Easterly waves of converging and diverging winds  Atlantic Ocean hurricanes

10. © 2012 Pearson Education, Inc. Tropical Depressions and Tropical Storms  Tropical Depression  Tropical disturbance wind speeds increase and begins to spin  A low pressure center is formed  Tropical Storm  Winds increase to 63 km (39 mi.) ph  Storm is given a name  Wind speeds are not at hurricane strength, but rainfall can be intense

11. © 2012 Pearson Education, Inc. Hurricanes  Not all tropical storms develop into hurricanes  Classified when winds reach 119 km (74 mi.) per hour  Environmental conditions  Thick layer of warm ocean water  Water must be warm and there must be deep  Steep vertical temperature gradient  Atmosphere must cool quickly with increasing altitude  Weak vertical wind shear  Strong winds aloft prevent hurricane development.

12. © 2012 Pearson Education, Inc. Hurricane Structure  Rain bands  Clouds that spiral inward around center  Counterclockwise in Northern Hemisphere  Increase in intensity towards the center of the hurricane  Eyewall  Innermost band of clouds  Contain the greatest winds and rainfall  Eye  Area of calm at center of the hurricane  Narrow at surface and wider at top

13. © 2012 Pearson Education, Inc. Hurricane Structure, cont.  Warm, moist air spirals upward around eyewall  Air rises, it loses moisture  Upward rotation draws air from eye, causing dry air to sink back into center  Upward rotation also causes air to flow out the top of the storm concentrated in exhaust jets  Allows additional warm air to feed bottom of the storm

14. © 2012 Pearson Education, Inc. Figure 10.14

15. © 2012 Pearson Education, Inc. Hurricane Paths and Demise  Movement is controlled by the Coriolis effect and steering winds  In Northern Hemisphere storms deflect to the right  Track west in trade winds and curve northwest and then northeast  Hurricanes can make a loop  In North Atlantic, steered by Bermuda High  As hurricane moves over land, it loses energy (warm water)  Can become extratropical cyclone

16. © 2012 Pearson Education, Inc. Extratropical Cyclones  Necessary conditions  Strong temperature gradient at surface usually along cold, warm or stationary fronts  Strong upper level winds provided by jet stream  Polar jet stream  Subtropical jet stream Figure 10.18

17. © 2012 Pearson Education, Inc. Polar and Tropical Jet Stream  Polar jet stream shifts from crossing the United States in the winter to crossing southern Canada in the summer  Subtropical jet stream crosses Mexico and Florida and is strongest in the winter  Large high-pressure ridges and low-pressure troughs cause jet streams to bend and producing waves or meanders  May also split in two around isolated high-pressures and reunite  Extratropical cyclones often develop in curves or divergences in jet streams

18. © 2012 Pearson Education, Inc. Polar and Tropical Jet Stream, cont.  Bending or splitting cause the polar jet stream to dip south and the subtropical jet stream to flow northeast  The southern branch of a split polar jet stream in the Pacific Ocean brings warm moist air out of the tropics  West Coast forecasters refer to the flow of warm moist air as the Pineapple Express, because of its origin near Hawai’i  Nor’easters form when bends of the polar and subtropical jet streams begin to merge off the southeastern coast of the United States

19. © 2012 Pearson Education, Inc. Extratropical Cyclone Development  Low-pressure center develops along frontal boundary  Cold front on southwest, warm front on east  Conveyor belt of cold air circulates counter-clockwise  Warm air is wedged to the east  Conveyor belt of warm air rises on the southeast side creating a comma  Conveyor belt of dry air aloft feeds the cyclone from behind the cold front  Cold front wraps around the warm front, causing an occluded front develop trapping warm air aloft  Cold air completely displaces the warm air, pressure gradient weakens and storm dissipates

20. © 2012 Pearson Education, Inc. Figure 10.20

21. © 2012 Pearson Education, Inc. Figure 10.21

22. © 2012 Pearson Education, Inc. Geographic Regions at Risk for Cyclones: North America  Hurricanes threaten contiguous United States, Puerto Rico, the Virgin Islands, and U.S. territories in the Pacific Ocean  They are a lesser threat to Hawai’i and Atlantic Canada  On the Pacific coast, hurricanes strike Baja California and the west coast of the Mexican mainland Figure 10.22

23. © 2012 Pearson Education, Inc. Atlantic Hurricane Paths  West toward East coast of Florida, sometimes passing over Caribbean  Move out into the Atlantic Ocean to the northeast  Westward over Cuba and into the Gulf of Mexico to strike the Gulf Coast  Westward to the Caribbean and then northeastward skirting the East Coast  May strike the continent from central Florida to New York Figure 10.17

24. © 2012 Pearson Education, Inc. Figure 10.24

25. © 2012 Pearson Education, Inc. Geographic Regions at Risk for Cyclones: Worldwide  Northwest Pacific is much more active than North Atlantic  Indian Ocean is also a very active hurricane zone  South Atlantic and southeast Pacific, rarely have hurricanes because of cold ocean water  Hurricanes do not form close to the equator because of the absence of the Coriolis effect

26. © 2012 Pearson Education, Inc. Figure 10.25

27. © 2012 Pearson Education, Inc. Geographic Regions at Risk from Cyclones, Summary  Tropical cyclones  East and Gulf Coasts  Hawaii and Atlantic Canada  Baja California and West Coast Mexico  Extratropical cyclones  Winter windstorms in Pacific Coast  Winter snow Sierra Nevada, Rocky Mountains and east  Spring and summer thunderstorms and tornadoes in United States and Canada

28. © 2012 Pearson Education, Inc. Cyclone Effects: Storm Surge  Local rise in sea level resulting from storm winds  Can be > 3 m (10 ft.)  Because of spinning, surge is greatest in right quadrant of storm as it makes landfall  Height is greatest near time of maximum winds  Height is also greater if landfall coincides with high tide

29. © 2012 Pearson Education, Inc. Figure 10.26

30. © 2012 Pearson Education, Inc. Effects on Storm Surge Magnitude  Largest effect from stress exerted by wind on water  Fetch refers to the area over which the wind blows  Larger fetch results in larger storm surge  Smaller effect from low atmospheric pressure in storm pulling up on water surface  Also depends on shape of coastline  Water level tends to increase continually as storm approaches

31. © 2012 Pearson Education, Inc. Cyclone Effects: High Winds  Described by Saffir-Simpson Scale  Decrease exponentially with landfall  Strongest recorded winds in United States from extratropical cyclone  Responsible for strong winds in blizzards and tornadoes

32. © 2012 Pearson Education, Inc. Cyclone Effects: Heavy Rains  Average hurricane produces trillion gallons of water  Rainfall from cyclones can cause inland flooding  Flooding affected by:  Storm’s speed  Land elevation over which the storm moves  Interaction with other weather systems  Amount of water in soil, streams and lakes prior to storm

33. © 2012 Pearson Education, Inc. Links to Other Natural Disasters  Coastal erosion  Flooding  Mass wasting  Other types of severe weather  Tornadoes, severe thunderstorms, snowstorms, and blizzards

34. © 2012 Pearson Education, Inc. Natural Service Functions of Cyclones  Source of precipitation  Redistribute warm air from tropics  Maintain ecosystems  Winds carry plants, animals, and microorganisms  Waves stir up deeper, nutrient-rich waters  Winds topple weak and diseased trees in forests  Waves break apart some corals

35. © 2012 Pearson Education, Inc. Human Interaction with Cyclones  Urbanization of vulnerable coastlines increases magnitude of the effect of cyclones  Destruction of sand dunes makes areas more susceptible to hurricane winds  Construction of seawalls and bulkheads reflect waves and contribute to beach erosion  Poor building materials and practices can make hurricanes more dangerous to people  Global warming may contribute to higher intensity and frequency of hurricanes in the future

36. © 2012 Pearson Education, Inc. Minimizing the Effects of Cyclones: Forecasting and Warnings  Forecast includes:  If it will make landfall  Where and when  Wind strength  Rainfall amount  Storm surge  Monitored by U.S. Hurricane Center, Canadian Hurricane Center  Hurricane watch means likely hurricane in 36 hours  Hurricane warning given when hurricane is likely within 24 hours or less

37. © 2012 Pearson Education, Inc. Forecasting Tools  Weather satellites  Detect early warning signs  Can not show wind speed  Aircraft  U.S. Air Force, NOAA airplanes fly into the storm to collect data  Doppler radar  Give information on rainfall, wind speed, and direction of the storm

38. © 2012 Pearson Education, Inc. Forecasting Tools, cont.  Weather buoys  Automated weather stations that give information at their locations  Computer models  Predict and track hurricane progress  Have vastly improved hurricane information  Still lacking in predicting storm intensity

39. © 2012 Pearson Education, Inc. Figure 10.32

40. © 2012 Pearson Education, Inc. Storm Surge Predictions  Predict the time and elevation of surge  Forecasters use wind speed, fetch and average water depth  Need detailed information on topography  Different elevations on land affect the storm surge  Computer models use central pressure, size, forward speed, track, wind speed, and seafloor topography

41. © 2012 Pearson Education, Inc. Hurricane Prediction and the Future  Deaths have decreased dramatically because of better forecasting, improved education, and greater public awareness  However, coastal populations are increasing, increasing risk

42. © 2012 Pearson Education, Inc. Perception of and Adjustment to Cyclones  Perception of hazard depends on personal experience  More experienced people may take hazard more seriously  More seasoned people may also take less precautions  Community adjustments to cyclone hazard  Warning systems  Evacuation plans and shelters  Insurance  Building design

43. © 2012 Pearson Education, Inc. Perception of and Adjustment to Cyclones, cont.  Personal adjustments to cyclone hazard  Be aware of hurricane season  Prepare homes and property for hazard  Obtain flood insurance  Install heavy shutters that can be latched  Learn evacuation route  Make a family emergency plan  Collect emergency supplies

44. © 2012 Pearson Education, Inc. End Hurricanes and Extratropical Cyclones Chapter 10