Hurricanes

• how wide are typical hurricanes?

  300 miles
• why do all hurricanes rotate?

  as they try to move from high to low pressure, they bend due to the coriolis force
• which way do hurricanes rotate in the southern hemisphere?

  clockwise
• which way do hurricanes rotate in the northern hemisphere?

  anticlockwise
• which way is deflection in the northern hemisphere?

  right
• which way is deflection in the southern hemisphere?

  left
• what are tropical cyclones?

  very big powerful destructive storms
• where are tropical cyclones called hurricanes?

  north Atlantic
• where are tropical cyclones called cyclones?

  Southern Hemisphere and Indian ocean
• where are tropical cyclones called typhoons?


  western pacific
• what must wind speeds exceed in order to be a tropical cyclone?

  74 miles per hour
• what is it called if a tropical cyclones looks the same but does not meet the sustained wind speed threshold (74mph)?

  a tropical storm
• what are hurricanes characterised by?

  strong winds exceed 74 mph, heavy rainfall, a rotating organised system of clouds and a warm core
• how many hurricanes occur each year around the world?

  50 to 100
• where do hurricanes form?

  over oceans
• where do we find hurricanes?

  between 5 - 30 degrees north and south of the equator, but not directly on the equator itself
• why do we rarely see hurricanes form on the equator?

  although there are high temperatures, there is no Coriolis force, meaning that the storm cannot rotate and be categorised as a hurricane
• when in the year do hurricanes form?

  from august to November
• when is hurricane season in the North Atlantic basin?

  from the 1st of June to the 30th of November, with peak activity typically seen in September
• where is majorly affected by the north atlantic basin?

  US states, Mexico and parts of Central America
• what are the six conditions needed for the formation of hurricanes?

  low pressure zones, warm oceans, high relative humidity, atmospheric instability, location more than 5 degrees from the equator and a low vertical wind shear
• what temperature must the ocean be to form a hurricane?

  warmer than 27 degrees C
• why do we need a high relative humidity to form hurricanes?

  so there is lots of water in the atmosphere which can rise and cool, condensing to form clouds
• why do we need to be more than 5 degrees away from the equator to form a hurricane?

  to provide the Coriolis force needed to drive rotation
• what are the paths taken by hurricanes like?

  steered by winds so sometimes very erratic
• what are the two types of speed which can be measured for a hurricane?

  speed of rotating winds and speed of forward propagation
• why do hurricanes decay extremely quickly once they hit land?

  they can no longer draw in warm water so begin to loose energy
• how long after making landfall does it take for a hurricane to loose so much energy that it is no longer fast enough to be classified as a hurricane rather than a tropical storm?

  six to twelve hours
• what are the three main structural features of hurricanes?

  the eye, the eye wall and the outer rainbands
• what is the eye?

  the central innermost area with calm, clear skies, low wind speed, low rain and low air pressure
• what is the eyewall?

  where rainfall and wind speeds are at a maximum
• what are the outer rainbands?

  zones of intense clouds and rainfall extending several hundreds of miles from the eye
• when is hurricane intensity the strongest?

  when the storm centre velocity and the hurricane wind velocity are going in the same direction
• which side is the faster velocity seen on in the northern hemisphere?

  eastern
• which side is the faster velocity seen on in the southern hemisphere?

  western
• why is there a greater velocity on one side of the hurricane than the other?

  on one side of the hurricane the velocities add together, whereas on the other side they are subtracted