Hurricane Formation

• Tropical cyclone


  A rotating low pressure weather system that has organized thunderstorms in the northern hemisphere
• Hurricane


  A tropical cyclone with maximum sustained winds of at least 74 miles per hour
• Stages of hurricane development

  1. Tropical disturbance/wave

  2. Tropical depression

  3. Tropical storm

  4. Hurricane
• Tropical disturbance/wave


  • Massive thunderstorms with slight wind circulation
• Tropical depression


  • More organization with several closed isobars, winds up to 39 mph
• Tropical storm


  • Greater organization, more isobars packed together, winds 39-73 mph
• Hurricane


  • Winds exceed 74 mph
• Saffir-Simpson hurricane scale categories

  • Category 1
  • Category 2
  • Category 3
  • Category 4
  • Category 5
• Requirements for hurricane formation

  • Warm and moist air
  • Warm sea surface temperatures (above 80°F)
  • High humidity in lower atmosphere
  • Converging surface winds
  • Trigger (e.g. tropical wave)
• Peak sea surface temperatures in the Atlantic occur in August through October
• The equator cannot produce hurricanes due to lack of Coriolis force
• Intertropical Convergence Zone (ITCZ)


  Area near but not on the equator where converging winds can trigger hurricane development
• Tropical waves


  Precursors to hurricane development that move off the West African coast
• Hurricane anatomy


  • Eye
  • Eye wall
  • Spiral rain bands
• Warm moist air spirals upward through the eye


  Cool dry air descends into the eye
• Hurricanes dissipate when they move over cold water or land, losing their energy source
• Hurricane Maria in 2017 was a very strong Category 5 hurricane that caused extensive damage in Puerto Rico