Saturday, January 4, 2020

Categories of Hurricanes

The Saffir-Simpson Hurricane Scale sets categories for the relative strength of hurricanes that may impact the United States based on the sustained wind speed. The scale places the storms into one of five categories. Since the 1990s, only wind speed has been used to categorize hurricanes. To estimate wind speed, the wind and wind gusts are measured over some period of time (typically one minute) and are then averaged together. The result is the highest average wind observed within a weather event.   Another measurement of weather is the barometric pressure, which is the weight of the atmosphere on any given surface. Falling pressure indicates a storm, while rising pressure usually means the weather is improving.   Category 1 Hurricane A hurricane labeled Category 1 has a  maximum sustained wind speed  of 74–95 miles per hour (mph), making it the weakest category. When the sustained wind speed drops below 74 mph, the storm is downgraded from a hurricane to a tropical storm. Although weak by hurricane standards, a Category 1 hurricanes winds are dangerous and will cause damage. Such damage could include: Roof, gutter, and siding damage to framed homesDowned power linesSnapped tree branches and uprooted trees In a Category 1 hurricane, coastal storm surge reaches 3–5 feet and the barometric pressure is approximately 980 millibars. Examples of Category 1 hurricanes include Hurricane Lili in 2002 in Louisiana and Hurricane Gaston, which hit South Carolina in 2004. Category 2 Hurricane When the maximum sustained wind speed is 96–110 mph, a hurricane is called a Category 2. The winds are considered extremely dangerous and will cause extensive damage, such as: Major roof and siding damage to framed homesMajor power outages that could last days to weeksMany uprooted trees and blocked roads Coastal storm surge reaches 6–8 feet and the barometric pressure is approximately 979–965 millibars. Hurricane Arthur, which hit North Carolina in 2014, was a Category 2 hurricane. Category 3 Hurricane Category 3 and above are considered major hurricanes. The maximum sustained wind speed is 111–129 mph. Damage from this category of hurricane is devastating: Mobile homes destroyed or heavily damagedMajor damage to framed homesMany uprooted trees and blocked roadsComplete power outages and unavailability of water for several days to weeks Coastal storm surge reaches 9–12 feet and the barometric pressure is approximately 964–945 millibars. Hurricane Katrina, which struck Louisiana in 2005, is one of the most devastating storms in U.S. history, causing an estimated $100 billion in damage. It was rated Category 3 when it made landfall.   Category 4 Hurricane With a maximum sustained wind speed of 130–156 mph, a Category 4 hurricane can result in catastrophic damage: Most mobile homes destroyedFramed homes destroyedHomes built to withstand hurricane-force winds sustain significant roof damageMost trees snapped or uprooted and roads blockedElectrical poles downed and outages lasting several last weeks to months Coastal storm surge reaches 13–18 feet and the barometric pressure is approximately 944–920 millibars. The deadly Galveston, Texas hurricane of 1900 was a Category 4 storm that killed an estimated  6,000 to 8,000 people. A more recent example is Hurricane Harvey, which made landfall at San Josà © Island, Texas, in 2017. Hurricane Irma was a Category 4 storm when it hit Florida in 2017, although it was a Category 5 when it struck Puerto Rico. Category 5 Hurricane The most catastrophic of all hurricanes, a Category 5 has a maximum sustained wind speed of 157 mph or higher. Damage can be so severe that most of the area hit  by such a storm could be uninhabitable for weeks or even months. Coastal storm surge reaches more than 18 feet and the barometric pressure is below 920 millibars. Only three Category 5 hurricanes have struck the mainland United States since records began: The Labor Day Hurricane of 1935 in the Florida KeysHurricane Camille in 1969 near the mouth of the Mississippi RiverHurricane Andrew in 1992 in Florida In 2017, Hurricane Maria was a Category 5 when it devastated Dominica and a Category 4 in Puerto Rico, making it the worst disaster in those islands histories. When Hurricane Maria hit the mainland U.S., it had weakened to a Category 3.

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