Tuesday, 4 October 2016

Hurricane Matthew batters Haiti.

One person has been confirmed dead and many more3 are unnaccounted for after Hurricane Matthew swept across Haiti on Monday 3 October 2916, The single cinfirmed fatality occured in the town of Port Salut, where a man described as too ill to be evacuated was swept away when a storm surge hit his home, but it is feared that many more could have died in remote communities on the west coast of the country. The country has reported extensive flooding, with the worst occuring around the towns of Les Cayes and Tiburon, where at least one major landslide has also been recorded. Landslides are a common problem after severe weather events, as excess pore water pressure can overcome cohesion in soil and sediments, allowing them to flow like liquids. Approximately 90% of all landslides are caused by heavy rainfall.

Raifall in Port-au-Prince during as Hurricane Matthew passed over Haiti on Monday 3 October 2016. Carlos Garcia Rawlins/Reuters.

Matthew was classed as a Catagory Four storm at the time when it hit Haiti (i.e. a storm with sustained winds in excess of 181 kilometers per hour), making it the most powerfull storm to make landfall in thre Caribbean for almost a decade, and is reported to have brought with it windspeeds of up to 230 kilometers per hour, as well as over a meter of  rianfall and significant storm surges. Around 340 000 people were evacuated from low-lying areas of Haiti ahead of the storm, and about 13 000 people from the neighbouring Dominican Republic. Evacuations are currently underway in Cuba, where the storm is expected to make landfallwithin the next 24 hours.

Floodwaters near Port-au-Prince during as Hurricane Matthew passed over Haiti on Monday 3 October 2016. Reuters.

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.

See also...

http://sciencythoughts.blogspot.co.uk/2016/09/tropical-storm-hermine-makes-landfall.htmlTropical Storm Hermine makes landfall in Florida.                                                      Tropical Storm Hermine made landfall close to...
http://sciencythoughts.blogspot.co.uk/2015/08/tropical-storm-erika-kills-at-least-25.htmlTropical Storm Erika kills at least 25 in the Caribbean.                                                       At least 36 people are known to have died and over 50 more are...
http://sciencythoughts.blogspot.co.uk/2012/10/hurricane-sandy-causes-devastation-in.htmlHurricane Sandy causes devastation in Jamaica.                                               Hurricane Sandy, the eighteenth named tropical storm in the Caribbean this season, struck Jamaica five miles east of the capitol, Kingston, arriving from the...
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