Six people are known to have died and 350 000 people have been evacuated from coastal areas after Cyclone Huhud hit the city of Visakhapatnam on the coast of Andhra Pradesh State, India, on Sunday 12 October 2014. Three deaths were recorded in Andhra Pradesh, and three in Odisha State (formerly Orissa), which is to the north, and many low lying coastal areas have been inundated by as much as 2 m of water. Sustained wind speeds as high as 205 kilometers per hour were recorded as the storm passed over Visakhapatnam (a sustained wind speed implies that this wind speed was maintianed fro over a minute), making the storm a Catagory 3 Cyclone. For many years such cyclones have been associated with very high mortality rates in India, but the practice of mass evacuations implemented in the past few years has sharply reduced the death toll.
A man rescuing a woman from a storm surge on a beach in Gopalpur, Odisha. Reuters.
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 path og Cyclone Huhud as it passed over the Indian Coast. Joint Typhoon Warning Center/National Atmospheric and Oceanic Administration.
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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Visakhapatnam
Visakhapatnam
