Twenty two people have been confirmed dead after Cyclone Ockhi swept across the Lakshadweep Archipelago, part of the Indian State of Kerala, on Saturday 2 December 2017. The majority of the deaths occurred in the islands' coastal communities and fishing fleet, which has been scattered by the storm, with over 500 fishermen rescued by vessels from the Indian Navy. Coastal communities and fishing vessels from the Keralan mainland have also been badly hit, as have those in Tamil Nadu and Sri Lanka, where at least seven people have died.
Storm damage in Kanyakumari District, Tamil Nadu following the passage of Cyclone Ockhi. European Commission/Flickr.
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 Winston till 07.00 GMT on Tuesday 28 March 2017 (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.
Storm damage in Colombo, Sri Lanka, following the passage of Cyclone Ockhi. Lakruwan Wanniarachchi/AFP.
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