1. Unit 3.c. – Extreme weather events and their impact on people and property -Hurricane formation & structure -Case study of one hurricane to illustrate: - its effects on people & property -protective measures used to reduce loss of life and damage to property

2. Names: hurricanes (Atlantic Ocean) typhoons (Pacific Ocean) tropical cyclones (Indian Ocean) CHARACTERISTICS: Intense system of low pressure –Very low troughs, 930mb or less –About 50 per yr off W Africa of which 10% form a full hurricane Characterised by winds of extreme velocity & torrential rainfall Develop over warm tropical seas (+26C) & where there is depth to the ocean -Constant supply of warm moist air evaporating is the fuel -RH must be greater than 60% -Need a large area of uniform temp., pressure & humidity Move generally from E to W - In N hemisphere move to NW and then to NE Most form in autumn when sea temp. are highest & in the trade wind belt

3. More characteristics: Located between 5-20 degrees N & S of the equator -Hurricane free belt next to the equator because of a very weak coriolis force (0-5 degrees) -Rotation increases poleward giving the required ‘twist’ therefore most hurricanes form bet. 5-8 degrees N or S - form after ITCZ has moved to its most northerly extent enabling air to converge at low levels Diameter of 200-500km Towering cumulonimbus clouds up to 12km Very quiet, calm eye of 30-50km where air is sinking 90% of deaths and injuries are caused by storm surge, heavy rain and strong winds

4. Characteristics continued: Average wind speeds 200km/hr (can reach 250km/hr) 3 classes of storms: 1.Tropical depression – thunderstorms with a defined circulation, max. winds of 60km/hr 2.Tropical storm – winds up to 118km/hr 3.Hurricanes – anything above 119km/hr

5. Formation Small scale instability Warm, humid air rises Rotation of the earth gives rise to a twist & the system revolves Large amounts of latent heat energy released through condensation Instability draws in more humid air, increases the size of the system System is self growing as long as there is a supply of warm, moist air

6. Characteristics of eye: - Eye develops when storm has reached maturity -Subsiding air 30-50km in diameter -Light winds, clear skies, high temp. -decending air increases instability by warming & exaggerates the storm’s intensity Decline of storm: -rapidly declines once the source of heat is removed i.e. when it moves over colder water or a land surface increased friction & cannot supply sufficient moisture -average lifespan of a tropical cyclone is 7-14 days

7. Popular topics in exams: There is a general falling trend in deaths from hurricanes e.g. the 5 highest figures were before 1939. Why? Better predictions i.e. use of aircraft Better evacuation / more forceful evacuation Better warning systems Better hospitals / medical care Better structure of buildings Better prepared for hurricanes, education on precautions

8. Popular topics in exams: There is a general trend of increasing costs of hurricane damage in million $ as time progresses. Why? Rising population therefore more personal belongings Marinas along the Gulf State house expensive yachts etc. Expensive housing Improved infrastructure of airports, bridges, flyovers etc would need repaired

9. Popular exam topics Why do LEDCs suffer more from the after effects of hurricanes than MEDCs?

10. Past short questions 1. For a mature hurricane what is the: -Max. cloud height -Diameter -Pressure -Max. wind speed (3) Jan 04 2. Explain why hurricanes form in tropical areas where there is a high ocean temperature.(3) Jan 04 3. Why do hurricanes not form between 5 N and 5 S of the equator? (2) Jan 04 4. Describe and explain the relationship between the development of hurricanes and a sea temperature of above 27C. (5) Jan 03

11. Past long questions (12 marks) 1.With reference to your case study of a hurricane, describe the protective measures used to reduce loss of life and damage to property. Jan 2003 2.With reference to your case study, describe the effects of a hurricane on people and property. June 2004 3.With reference to extreme weather events: * describe and explain the formation of hurricanes; and * describe the effects of one hurricane you have studied on people and property. Jan 2005

12. Research task Case study is Hurricane Katrina 2005 1.Make a list of causes 2.List the main warnings given 3.List the main precautions taken, including evacuation 4.What emergency aid was provided 5.How successful were the government warnings & provision of aid? 6.List the effects of the hurricane on: a) people b) property