Page 91 - The World About Us

Irma damage
1.1.1
1.1.1
2.2.3
2.3.5

How and why do tropical revolving storms develop?

Tropical storms need very clockwise in the Northern Dangerous Tropical Storms
par cular condi ons to form. They Hemisphere.
need a sea temperature in excess of Air spiralling upwards generates Cyclone Nargis was a category 4 storm which
27 C. This warms the air above it. The bands of cumulonimbus thunder raced up the Bay of Bengal in May 2008. The
sea also needs to be deep enough, at clouds and intense rainfall. intense low pressure of 962mb. sucked up the
surface of the sea and added to the strong winds
least 50-60 metres, to con nue to and waves. The low lying Irrawaddy Delta was
power the storm once it develops. Increasing wind speeds peak close inundated, with storm waters reaching 40km
to the eye wall. Where the eye wall
Tropical storms tend to develop in passes over land, damage is o en inland. An es mated 138,000 died in Myanmar
zones 500km from the Equator. This considerable. Should the following with 84,000 dead in the villages of Labu a district.
allows for the Coriolis Force to be eye wall pass over the same loca on, Winds reached gusts of 215 km/hr and damage
strong enough to make the storm was es mated at $12.95 billion.
this will be significantly increased.
revolve. Hurricane Katrina made landfall in Florida in
Winds now blow in the opposite
August 2005 but then passed into the Gulf of
As warm air rises over the warm direc on further threatening already Mexico, developing into a category 5 storm with
sea, it begins to cool resul ng in weakened structures. gusts of 280km/h. It made landfall again in
condensa on and cloud forma on. Louisiana. The storm surge, caused by pressure as
At the centre of the cyclone is the
Latent heat released during conden- low as 902mb, accompanied by a failure of levees
eye. This is normally 15-30km across,
sa on further fuels the upli of air. on the Mississippi river, resulted in flooding to 80%
although it can be as small as 3km
of New Orleans. Fatali es were es mated at over
As the storm rises to the and as large as 370km. The eye is a
1,800 and damage exceeded $108 billion.
Tropopause at around 15-17km, it is zone of sinking air at the centre of
spun by the Coriolis Force. Tropical the rota ng storm which is defined
storms rotate clockwise in the by gentle winds and clear skies: the
Southern Hemisphere and an - calm at the eye of the storm.

Fig.244 Tacloban devastated by Typhoon Haiyan.
Typhoon Haiyan, also known as Super Typhoon
Fig.242 The structure of a tropical rota ng storm in the Northern Hemipshere. Yolanda, hit the Philippines in November 2013. The
Category 5 storm saw gusts of 315km/hr and
The Coriolis Force North Pole Earth’s rota on pressure as low as 595mb. Eleven million people
were affected, with 6,300 people killed in the
South-north Philippines. Here the city of Tacloban was all but
We have already seen how the Trade path
Winds and the mid-la tude westerlies Actual destroyed. Damage was es mated at $2.16 billion.
appear to be deflected to the right in the path Hurricane Harvey made landfall, as a category
Northern Hemisphere and to the le in 4 storm, on the Texas Gulf coast in August 2017.
the Southern Hemisphere (page 86). This Equator Harvey dumped 77cm of rain over Houston in two
is also true of ocean currents, which are days. 88 people were killed, mostly by the floods.
Damage was es mated at $180 billion.
also deflected by the rota on of the Earth
around its axis. Actual Fig.245 Texas under Hurricane Harvey’s flood waters.
path
The Earth spins much faster at the North-
Equator than the Poles, as its diameter is south path
greatest at 0 la tude. Wind (moving air) South Pole
travelling north or south from the Equator Fig.243 The Coriolis Force.
is not fixed to the surface of the planet. It is deflected to the right (Northern
Hemisphere) or le (Southern Hemisphere) as the Earth spins underneath it. East
bound winds tend to be deflected towards the Equator while westbound winds
deflect towards the poles. This is the Coriolis Force and it is this deflec on which
creates the spin in a tropical storm.

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Extreme weather conditions cause different natural weather hazards.