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Climate: Hurricane Basic Detail


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A Session to introduce the key ideas behind hurricane development and movement, including basic details on size, speeds and associated features

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Climate: Hurricane Basic Detail

  1. 1. Cyclones in Detail Features and energy
  2. 2. Definitions <ul><li>Cyclones - mix of multiple thunderstorms forming a huge spiraling system </li></ul><ul><li>Cyclone is the generic name for a massive rotating storm system, at their strongest they are called hurricanes (Caribbean and America), Typhoons (Pacific Ocean), Cyclones (India and Australia) and Willy Willies in Australia </li></ul>
  3. 3. Hurricanes, Cyclones and Typhoons <ul><li>Deep areas of low pressure </li></ul><ul><li>In the tropics </li></ul><ul><li>Forms over Warm sea surfaces </li></ul><ul><li>Strong and violent winds and heavy rain to adjacent land </li></ul><ul><li>Name dependant on location! Essentially the same </li></ul>
  4. 4. Cyclones/hurricanes/Typhoons <ul><li>Formation - very little evidence as to exact method of formation </li></ul><ul><li>Must have - </li></ul><ul><li>Warm tropical seas (>26 degrees) and considerable depth </li></ul><ul><li>In autumn - highest water temp </li></ul><ul><li>In trade wind belt - surface winds warm as the blow towards equator </li></ul><ul><li>Between 5 and 20 north or south </li></ul>
  5. 5. Basics <ul><li>0. A tropical depression becomes a hurricane when its sustained recorded winds reach 74 mph. </li></ul><ul><li>Note: These systems are rated from 1 – 5 on the Saffir-Simpson Scale (&quot;S/S Scale&quot;) developed in the early 1970s by Herbert Saffir, Consulting Engineer, and Robert Simpson, then director of the National Hurricane Center. </li></ul>
  6. 6. Once formed <ul><li>Always move westwards - unpredictable courses swing towards poles when hit land (global heat transfer mechanism) </li></ul><ul><li>Can have diameter of 650 KM </li></ul><ul><li>Needs temp, pressure and humidity to be uniform over a large area in the lower troposphere for a long period of time </li></ul><ul><li>Leads to strong surface winds and intense low pressure near the surface </li></ul>
  7. 7. <ul><li>To enable movement, must have continual heat to maintain rising air currents and moisture </li></ul><ul><li>Once mature develops the eye (30 -50KM, subsiding air, light winds, clear skies and high temperatures) </li></ul><ul><li>Once onto a land surface, temperature drops and the hurricane loses energy, has to overcome more friction and does not have enough moisture. Most hurricanes last 7 to 14 days </li></ul>
  8. 8. Pressure <ul><li>characterized by a centre of extremely low surface air pressure with a steep pressure gradient from the centre outward producing a series of closed concentric isobars . </li></ul><ul><li>Sea-level air pressure varies from near the atmospheric mean value of 1013 mb in the environment (at a radius of 1000 km from the storm centre) to below 900 mb in extreme cases. </li></ul><ul><li>The lowest minimum pressure ever recorded in the centre of a hurricane was 870 mb. </li></ul>
  9. 9. Hurricane Anatomy <ul><li>The main parts of a hurricane are the rain bands on its outer edges, the eye, and the eye wall. </li></ul><ul><li>Air spirals in toward the centre in a counter-clockwise pattern, and out the top in the opposite direction. </li></ul><ul><li>In the very centre of the storm, air sinks, forming the cloud-free eye of high pressure </li></ul>
  10. 10. Storm Surges <ul><li>Are associated with typhoons/hurricanes/cyclones </li></ul><ul><li>Pressure drop n the weather system allows the sea water to rise above normal </li></ul><ul><li>Water piled up in large waves by high winds </li></ul><ul><li>Can be up to 6 meters above usual levels </li></ul>
  11. 11. Hurricane Size <ul><li>Typical hurricanes are about 300 miles wide </li></ul><ul><li>Size is not necessarily an indication of hurricane intensity </li></ul><ul><li>Hurricane-force winds can extend outward to about 25 miles from the storm centre of a small hurricane and to more than 150 miles for a large one. </li></ul><ul><li>The area over which tropical storm-force winds occur is even greater ranging as far out as almost 300 miles from the eye of a large hurricane. </li></ul>
  12. 12. Hurricane Circulation <ul><li>In the northern hemisphere, hurricane winds circulate around the centre in a counter-clockwise fashion. </li></ul><ul><li>This means that the wind direction at your location depends on where the hurricane's eye is. </li></ul><ul><li>A boat on the northern edge of the orange area in Hurricane Fran (right) would experience winds from the east, while a boat on the southern edge would have westerly winds </li></ul>
  13. 13. Hurricane path <ul><li>Depends on complex interactions between the storm with its own internal circulations and the earth's atmosphere. </li></ul><ul><li>The air in which the hurricane is embedded is a constantly moving and changing &quot;river&quot; of air. </li></ul><ul><li>Other features in that flow, such as high and low pressure systems, can greatly alter the speed and the path of the hurricane. </li></ul><ul><li>In turn, it can modify the environment around the storm. . </li></ul>
  14. 14. Hurricane speed <ul><li>Typically, a hurricane's forward speed averages around 15-20 mph. </li></ul><ul><li>However, some hurricanes stall, often causing devastatingly heavy rain. </li></ul><ul><li>Others can accelerate to more than 60 mph. Hurricane Hazel (1954) hit North Carolina on the morning of 15 October; fourteen hours later it reached Toronto, Canada where it caused 80 deaths. </li></ul><ul><li>Some hurricanes follow a fairly straight course, while others loop and are difficult to forecast </li></ul>
  15. 15. Prediction <ul><li>Regular occurrence , clearly defined hurricane seasons </li></ul><ul><li>America - Aug to October </li></ul><ul><li>Australia and pacific </li></ul><ul><li>India/Bay of Bengal </li></ul><ul><li>Therefore clear expectation of when will occur </li></ul><ul><li>Once formation has started clearly visible on satellite imagery </li></ul><ul><li>As they are so easy to spot, why are there such huge differences? </li></ul>