Thursday 24 May 2018

Seventeen missing after Cyclone Mekunu sweeps across the Socotra Islands.

Seventeen people are still missing after Cyclone Mekunu swept across the Yemeni Socotra Island group on Wednesday 23-Thursday 24 May 2018. Full details of the missing persons have not been released, but it is understood that four were members of the crew of one of two vessels that sank during the strom, while another three were in a car that was swept away by floodwaters. The storm is expected to make landfall on the southern part of the Arabian Peninsula this weekend, either in eastern Yemen or southern Oman.

Receding floodwaters on Socotra Island (the largest island of the Socotra group) on 24 May 2018. Abdullah Morgan/AP.

Tropical storms are caused by solar energy heating the air above the oceans, which causes the air to rise leading to an inrush of air. If this happens over a large enough area the inrushing air will start to circulate, as the rotation of the Earth causes the winds closer to the equator to move eastwards compared to those further away (the Coriolis Effect). This leads to tropical storms rotating clockwise in the southern hemisphere and anticlockwise in the northern hemisphere.These storms tend to grow in strength as they move across the ocean and lose it as they pass over land (this is not completely true: many tropical storms peter out without reaching land due to wider atmospheric patterns), since the land tends to absorb solar energy while the sea reflects it.

The passage of Cyclone Mekunu till 12.00 GMT on Thursday 24 May 2018 (thick line) with its predicted future path (thin line, circles represent the margin of error on the predictions). Colours indicate the strength of the storm. Tropical Storm Risk.

The low pressure above tropical storms causes water to rise there by ~1 cm for every millibar drop in pressure, leading to a storm surge that can overwhelm low-lying coastal areas, while at the same time the heat leads to high levels of evaporation from the sea - and subsequently high levels of rainfall. This can cause additional flooding on land, as well as landslides, which are 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.

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