Hurricanes and the measure of destruction

Hurricane Harvey, viewed from the International Space Station.
Hurricane Harvey, viewed from the International Space Station.
Image: NASA.
With Houston residents still recovering from Hurricane Harvey, weather forecasters now are watching another storm skulk across the Atlantic–Irma.

       So far, this one is a tropical storm, not a hurricane. But what is the difference? Here are some definitions:

Storm: A storm is “a disturbance of the atmosphere marked by wind and usually by rain, snow, hail, sleet, or thunder and lightning,” according to Merriam-Webster online. 

Cyclone: This is defined as “an atmospheric closed circulation rotating counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere,” according to the National Hurricane Center at the National Ocean and Atmospheric Administration (NOAA).

Tropical depression: NOAA defines this as a tropical cyclone in which the maximum sustained surface wind speed is 38 mph or less.

Tropical storm: Merriam-Webster online defines a tropical storm as a “tropical cyclone with strong winds of over 39 mph but less than hurricane intensity.” 

Hurricane (or typhoon): This designation has to do with location and strength. A hurricane is a tropical cyclone with sustained surface winds of 74 mph or more. “The term hurricane is used for Northern Hemisphere tropical cyclones east of the International Dateline (which passes through the Pacific Ocean), to the Greenwich Meridian (in England),” according to the NOAA. “The term typhoon is used for Pacific tropical cyclones north of the Equator (and) west of the International Dateline.”

Hurricane categories: In order to warn residents of the severity of a storm, NOAA uses a the Saffir-Simpson hurricane wind scale. The scale was developed in 1969 by wind engineer Herb Saffir (1917-2007) and meteorologist Robert H. Simpson (1912-2014). Here is how the scale is defined by NOAA:

  • Category 1 --The hurricane comes with winds ranging from 74-95 mph. Branches could snap and homes could have roof damage.
  • Category 2 -- The hurricane has more severe winds, 96-110 mph. Beyond roof damage, residents can expect power loss and trees down.
  • Category 3 -- The hurricane is considered a major storm. Winds are 111-129 mph. Even well-built homes could experience damage. Power outages are possible, and trees could be snapped or uprooted.
  • Category 4 -- Also considered a major storm, the hurricane will have winds of 130-156 mph. Along with damage to utilities and homes, most of the area will be “uninhabitable for weeks or months,” according to NOAA.            
  • Category 5 -- The most severe hurricane has winds of 157 mph or higher. Expect extensive and catastrophic damage.

     To know more:


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