Thursday 6 September 2018

Tropical Storm Gordon makes landfall on the Gulf Coast of the US, causing one death and widespread flooding.

Tropical Storm Gordon made landfall about 50 km to the east of Biloxi, Mississippi, on Wednesday 5 September 2018, bringing with it winds of slightly under 115 kilometres per hour (the point at which it would be upgraded to a hurricane), and widespread flooding, along the costs of Lousiana, Mississipi, Alabama and the Florida Panhandle. One person has been reported dead due to the storm, an as yet un-named child killed in Escambia County, Florida, by a tree falling onto a mobile home, and about 50 000 people were left without power, mostly in Alabama.

Emergency services in Escabia County, Florida, attend the scene of the only known fatality associated with Tropical Storm Gordon, a child killed when a falling tree hit a mobile home. WCCO.

Tropical storms are caused by the warming effect of the Sun over tropical seas. As the air warms it expands, causing a drop in air pressure, and rises, causing air from outside the area to rush in to replace it. If this happens over a sufficiently wide area then the inrushing winds will be affected by centrifugal forces caused by the Earth's rotation (the Coriolis effect). This means that winds will be deflected clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere, eventually creating a large, rotating Tropical Storm. They have different names in different parts of the world, with those in the northwest Atlantic being referred to as hurricanes.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.

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