Tropical storms

• Tropical storms are rotating, intense low-pressure systems (below 950mb)
• Tropical storms are known as

  • Typhoons in the South China Sea and west Pacific Ocean
  • Hurricanes in the Gulf of Mexico, Caribbean Sea and west coast of Mexico
  • Cyclones in the Bay of Bengal, Indian Ocean and northern Australia
• Tropical storms develop over the warm tropical oceans between 5° and 30° north and south of the equator
• Relationship between tropical storms and global circulation

  1. Equatorial regions receive intense solar heating raising ocean temperatures

  2. Warm, moist air rises, leading to an intense low-pressure zone between the two Hadley cells (Intertropical Convergence Zone)

  3. Generates thunderstorms, strong winds and intense rainfall at the surface

  4. Dry air descends creating a high-pressure zone at the surface

  5. Pressure gradients and air rushes to the low-pressure zone generating the winds of the forming tropical storm

  6. Trade winds move in a westerly direction from the equator

  7. Coriolis effect starts the air spinning from 5° north and south of the equator
• The spin is anti-clockwise (anticyclone) in the northern hemisphere but clockwise (cyclone) in the southern hemisphere as they are low-pressure systems
• The greater the low-pressure, the greater the winds, the greater the spin and the larger the tropical storm becomes
• Causes of tropical storms

  • Sea temperatures must be 27°C and above
  • They only form between 5° and 30° north and south of the equator
  • The rising air draws further moist, warm air up from the ocean's surface, generating stronger winds
  • The air spirals upwards, cools, condenses and forms large cumulonimbus clouds
  • Cold air sinks at the centre, creating a calm, dry area known as the eye of the storm
  • Tropical storms will die out if the heat energy and moisture from the ocean are no longer available to drive the storm
• Characteristics of tropical storms

  • Lasting 7-14 days
  • Heavy rainfall
  • High wind speeds (over 119 kmph)
  • High waves and storm surges
  • Vary in diameter (100-1000km)
  • Winds spiral rapidly around a calm central area known as the eye, with descending cold air, low pressure, light winds, no clouds or rain
  • The strongest and most destructive winds are found within the eyewall, with spiralling storm clouds, torrential rainfall and low temperatures
  • Rated on the five-point Saffir-Simpson scale based on wind speeds
• Tropical storms are considered major when they reach category 3 and have wind speeds between 111-129 miles (178-208 kilometres) per hour
• A category 5 storm can deliver wind speeds of more than 157 miles (252km) an hour
• As winds contact and begin passing over land/rough terrain


  They become slower
• Global temperatures are set to rise as a result of global warming

  • More of the world's oceans will be above 27° C, therefore, more places across the world will experience tropical storms
  • Oceans will stay at 27°C or higher for longer during the year, which will increase the annual number of tropical storms
  • Higher temperatures will mean storms will be stronger, more frequent and cause more damage
• If global ocean temperatures continue to rise

  • Tropical storms may affect areas further from the Equator
  • They could affect parts of the sub tropics/the South Atlantic/NE USA
  • They could have a broader distribution/effect on larger parts of the world