Science behind hurricanes

Hurricane Irene is the first named storm and the first major hurricane in 2011.  There is much news coverage about this at this time of the year.  It is very important to track these huge storms and to make accurate predications about their movements. Many people live in areas affected by hurricanes.

News agencies report the path of the hurricane to notify residents of the area who may be impacted.  If the National Hurricane Center scientists believe a hurricane is threatening to reach a populated area within 24 hours, they will issue a hurricane warning. People prepare by gathering and sheltering property and boarding up homes and businesses. Sometimes people will even be evacuated from an area if the forecast calls for an extremely strong storm. Many lives have been saved by these preparations.

Did you ever wonder how these names get assigned? The National Weather Service names hurricanes to quickly identify them. The names are assigned in alphabetical order alternating between female and male names. There are separate lists of names for hurricanes in the Atlantic and Pacific oceans.

Origin of hurricane is WIND. The hurricane takes its name from the West Indian word huracan which means “big wind.” Storms that occur over the Atlantic or the eastern Pacific Oceans are called hurricanes. The same kind of storm that forms over the western Pacific or Indian Oceans is called a typhoon. This name comes from the Chinese word taifun or “great wind.”

STRONG WINDS.  Hurricanes have top wind speeds of at least 74 miles per hour, but wind speed can reach 180 miles per hour. The closer you are to the storm’s center, the faster the wind will be. The top wind speed will be reached within 60 miles from the center of the hurricane. As you move away from the center, wind speed is slower. At 300 miles from the center, the wind speed may be only 18 miles per hour.

How to predice the hurricane? To study conditions inside hurricanes, teams of pilots and weather scientists fly regular missions into these storms. They get measurements of wind speed, temperature, air pressure, and other weather conditions at different altitudes. These investigations help scientists make predictions about hurricane formation and movement.  NASA satellites are also flying above Hurricane Irene, providing forecasters at NHC with temperature, pressure, wind, and cloud and sea surface temperature data. All of those things are critical in helping forecasters determine how Irene will behave and track.

How do hurricanes form? Hurricanes and typhoons are not just violent winds. They are giant, whirling storms that develop in a special way.   The energy of a hurricane comes from the heat released when water vapor condenses to liquid water. The atmosphere above a tropical ocean is the only place enough warm, moist air is available to produce the energy necessary to create a hurricane.  Hurricanes form only in the tropics where extremely moist air and heat are concentrated over the ocean, near the equator.  Hurricanes develop during the season when it is a wet season (typically late spring to early autumn) and the water temperature is at least 80 degrees Fahrenheit both day and night.

Here is what’s going on:

  1. Evaporation of the warm water into the atmosphere over the ocean makes the air very moist.
  2. Winds blowing across the ocean in different directions begin to push masses of warm, moist air toward each other. This event is called convergence.
  3. When the air masses collide, the air in the center starts to rise, forming an updraft.
  4. At high altitudes, the moist air of the updraft begins to cool and water droplets form. These water droplets form clouds.
  5. Large cumulonimbus clouds begin to grow and thunderstorms develop.
  6. More thunderstorms form as more convergence and updrafts occur. If the thunderstorms do not dissipate, they may start to gather together. This formation is called a tropical disturbance. Many more thunderstorms join the disturbance. This weather event becomes large enough to be influenced by forces created from the Earth’s rotation.
  7. The tropical disturbance begins to swirl and becomes a vortex of thunderstorms. Updrafts are continuously pulling more air into the disturbance.
  8. When the winds begin to blow continuously at 23 miles per hour, the storm becomes a tropical depression.
  9. The tropical depression continues to gain power and becomes a tropical storm  when the wind speed becomes 40 miles per hour.
  10. At any time, the disturbance, depression, or storm can run out of hot, moist air and weaken or die out. If it continues to gain strength and reaches 74 miles per hour we call it a hurricane.

Check out the following experiment from Steve Spangleer science on how to simulate creating your own hurricane in a water bottle.


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