The Story Of Sandy

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Hurricane Sandy is sure to go down in the record books as one of the most “high-impact” storms ever observed and experienced.  Sandy was born on October 22, 2012 over the Caribbean Sea south of Jamaica, when “Tropical Depression 18” was upgraded to “Tropical Storm Sandy”.  During the following week, Sandy intensified into a hurricane, produced flooding rains and mudslides across portions of Jamaica, eastern Cuba, and Haiti, whipped up hurricane force winds, built 30-foot seas in the western North Atlantic, and brought a devastating storm surge to portions of New Jersey and New York.  Sandy also delivered winds near tropical storm force over the waters adjacent to the upper Florida Keys.  The expanding circulation of Sandy as it moved north over the Atlantic helped maintain a persistent, strong, northwest breeze over the eastern Gulf of Mexico and Florida Keys.  This trajectory piled up sea water, leading to several days of high tides and minor coastal flooding in some Keys communities adjacent to the Gulf, Florida Bay, and Blackwater Sound. Sandy has become infamous for the impact and devastation it wrought over a large area.  However, Sandy is noteworthy as well for bringing meteorological terms like “tropical cyclone”, “extratropical cyclone”, and “hybrid cyclone” into public discourse.  This is because Sandy went through a meteorological “conversion” or transition between the warm, tropical waters of the Caribbean Sea, and the autumn landscapes of the northeastern United States. So, what happened?  Why were hurricane warnings posted for Cuba, but not for Long Island Beach, New Jersey?  Why were all of these different meteorological terms floated about in the media?  These are good questions, and they all lie at the heart of a meteorological distinction between “tropical” low pressure systems and non-tropical low pressure systems.  This distinction mainly has to do with the means by which a low pressure system is energized, which, in turn affects intensification, weakening, structure, and the types of weather experienced.  A “hurricane” is a species of tropical low pressure system energized by the warm, moist air emanating from the tropical oceans.  Hurricanes grow by releasing this heat into the atmosphere near the storm center.  Hurricanes tend to be symmetric, containing compact wind fields with the most intense winds located within a donut-shaped area around a calm center (the eye).  Also, hurricanes typically are characterized by spiral rainbands which contain fast-moving squalls that become increasingly violent as you move from the outer periphery of the storm toward the eyewall, where the strongest winds are located.  Hurricanes weaken and disorganize when they move over land, or over cooler water because by doing so, they become deprived of their energy source.  Now, the typical “extra-tropical” cyclone (or wintertime cyclone) is a low pressure system energized by the horizontal temperature contrasts found in the atmosphere near jet streams.  These types of systems vary greatly in intensity, from small, weak, short-lived systems to the strong nor’easters and large marine gale centers common over the western North Atlantic Ocean.  Their structure is quite different from hurricanes in that the strongest winds typically are spread out over a large area, significant temperature differences occur across the system, and they tend to develop at higher latitudes over both land and ocean.  So, there are very real differences in both the meteorology and societal impacts of these two types of systems. Sandy was truly exceptional for several reasons including its size, intensity, and evolution from a tropical cyclone into an extra-tropical cyclone, during the time when most storm preparations and protective actions were occurring along the most populated section of the U.S. east coast. The NOAA/National Weather Service provides a variety of information in the form of messages and graphics for various weather-sensitive communities (aviation, marine, fire, and the general public) in addition to more direct consultation to core partners (emergency management, law enforcement, and search and rescue personnel) for the protection of life and property.  Most of these weather messages and graphics are tailored to specific weather hazards such as tornadoes, hurricanes, floods, and winter storms.  Sandy was an exceptionally big and violent low pressure system, which grew up as a hurricane and died as a winter storm, reaching its maximum maturity and intensity just as it was affecting the most populated metropolitan region in America.  As a result, Sandy challenged some prevailing assumptions regarding widespread hazardous weather and the manner in which associated societal impacts are communicated. Remember to be weather-ready, and stay safe!


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