Eight people have now been confirmed dead as Hurricane Dorian passed over the Bahamas and up the east coast of the United States. The hurricane swept past several Caribbean island nations between 25 and 30 August 2019, prompting evacuations and curfews, but causing little actual damage. However, over this period it was steadily gaining in strength, so that when it finally made landfall on Elbow Cay in the Bahamas it was a Category Five storm, with sustained winds in excess of 250 km per hour and gusts considerably stronger, and the strongest storm ever recorded to have made landfall from the Atlantic. The storm caused widespread devastation across the Abaco Islands and Grand Bahama, destroying thousands of homes causing widespread flooding and killing at least seven people - though this number is likely to be a severe underestimate due to the damage the storm has caused to the nation's infrastructure. Following this the storm has swept northward up the east coast of the United States, past Florida, Georgia, and South and North Carolina. The storm has brought flooding and high winds to these areas, with storm surges in excess of two metres and one confirmed death in North Carolina, but has been losing strength as it moves north and is now only a Category Two storm.
Flooding and damaged buildings in the Abaco Islands in the wake of Hurricane Dorian. Latrae Rahming.
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.
The path and strength of Hurricane Dorian. Thick line indicates the past path of the storm (till 3.00 pm GMT on Tuesday 4 September 2019), while the thin line indicates the predicted future path of the storm, and the dotted circles the margin of error at nine, twenty one, thirty three, forty five, sixty nine, ninety three and one hundred and seventeen hours ahead. Colour indicated the severity of the storm. Tropical Storm Risk.
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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