GEOGRAPHY IGCSE: TROPICAL STORMS. It contains: hurricanes, how hurricanes form, preparation and prediction, effects of tropical storms, case study hurricane Katrina 2005, impacts, responses, glossary.

1. IGCSE GEOGRAPHY
23. WEATHER & CLIMATE
TROPICAL STORMS
CASE STUDY:
HURRICANE
KATRINA 2005

2. The strongest tropical storms are called hurricanes,
typhoons or tropical cyclones. The different names all mean
the same thing.
If these huge storms start in the Atlantic off the west coast
of Africa, they are called hurricanes.
In an average year over a dozen hurricanes form over the
Atlantic Ocean and head westwards towards the Caribbean,
the east coast of Central America and the southern USA
(Florida).
Hurricanes may last as long as a month and although they
travel very slowly - usually at about 24 km/h (15 mph) -
wind speeds can reach over 120 km/h (75 mph).

3. Map showing path of Hurricane Sandy, 2012

4. Hurricanes need a lot of heat to form and a sea surface
temperature of at least 26°C, which is why they usually occur
over tropical seas. They also need to be between 5 and 20° north
or south of the Equator. It works like this:
a) When this warm and wet air rises, it condenses to form
towering clouds, heavy rainfall. It also creates a low pressure
zone near the surface of the water.
b) Rising warm air causes the pressure to decrease at higher
altitudes. Warm air is under a higher pressure than cold air,
so moves towards the ‘space’ occupied by the colder, lower
pressure, air. So the low pressure ‘sucks in’ air from the
warm surroundings, which then rises. A continuous upflow
of warm and wet air continues to create clouds and rain.

5. c) Air that surrounds the low pressure zone at the centre flows
in a spiral at very high speeds - anti-clockwise in the northern
hemisphere - at speeds of around 120 km/h (75 mph).
d) Air is ejected at the top of the storm – which can be 15km
high – and falls to the outside of the storm, out and over the
top, away from the eye of the storm. As this happens, it reduces
the mass of air over the ‘eye of the storm’ - causing the wind
speed to increase further. Some ejected air also cools and dries,
and sinks through the eye of the storm, adding to the low
pressure at the centre.
e) The faster the winds blow, the lower the air pressure in the
centre, and so the cycle continues. The hurricane grows stronger
and stronger.

6. f) Seen from above, hurricanes are huge circular bodies of thick
cloud around 450 km (300 miles) wide. The cloud brings heavy
rain, thunder and lightning.
g) In the centre is the eye of the hurricane, about 45 km across
(30 miles) across. Often there will be no clouds in the eye. Seen
from below it will seem calmer, with a circle of blue sky above.
The eye is formed because this is the only part of the hurricane
where cold air is descending.
h) In the northern hemisphere, the prevailing easterly tropical
winds tend to steer hurricanes toward land - although their
course is unpredictable. As hurricanes move inshore, their
power gradually reduces because their energy comes from
sucking up moist sea air.

7. The formation of a hurricane

8. Preparation and prediction techniques can be very different
in MEDCs and LEDCs.

9. MEDCs have the resources and technology to predict and
monitor the occurrence of storms, eg using satellites and
specially equipped aircraft.
They are also equipped to train the emergency services
appropriately and to educate people about necessary
precautions.
Storm warnings can be issued to enable the population to
evacuate or prepare themselves for the storm.
People can prepare by storing food and water or boarding up
their windows.

10. LEDCs are often less prepared.
They may rely on aid (sometimes reluctantly) from MEDCs for
the rescue and recovery process, as was the case with Cyclone
Sidr in Bangladesh, November 2007.

11. The intense winds of tropical storms can destroy whole
communities, buildings and communication networks.
As well as their own destructive energy, the winds generate
abnormally high waves and tidal surges.
Sometimes the most destructive elements of a storm are the
subsequent high seas and flooding.
MEDCs are better placed to reduce the effects of tropical
storms because they have more financial, educational and
technological resources to help deal with them.
They better able to observe and predict storm behaviour and
can invest in infrastructure to withstand storms - as well as
spending more money on repairing the damage caused.

12. Bangladeshi villager affected by cyclone Sidr
People affected by cyclone Sidr

13. Hurricane Katrina was the costliest natural disaster and one of
the five deadliest hurricanes in the history of the United
States.
The storm is ranked as the third most intense United States
landfalling tropical cyclone, behind the 1935 Labour Day
Hurricane and Hurricane Camille in 1969.
1,245 people died in the hurricane and floods, making it the
deadliest United States hurricane since the 1928 Okeechobee
hurricane.
Total property damage was estimated at $108 billion (2005
USD).

15. Katrina was a category 4 storm.
Storm surges reached over 6 metres in height.
New Orleans was one of the worst affected areas because it
lies below sea level and is protected by levees.
These protect it from the Mississippi River and Lake
Ponchartrain.
The levee defences were unable to cope with the strength of
Katrina, and water flooded into the city.
Despite an evacuation order, many of the poorest people
remained in the city.

16. People sought refuge in the Superdome stadium.
Conditions were unhygienic, and there was a shortage of
food and water.
Looting was commonplace throughout the city.
Tension was high and many felt vulnerable and unsafe.
1 million people were made homeless and about 1,200
people drowned in the floods.
Oil facilities were damaged and as a result petrol prices rose
in the UK and USA.

18. There was much criticism of the authorities for their handling
of the disaster.
Although many people were evacuated, it was a slow process
and the poorest and most vulnerable were left behind.
$50 billion in aid was given by the government.
The UK government sent food aid during the early stages of the
recovery process.
The National Guard was mobilised to restore and maintain law
and order in what became a hostile and unsafe living
environment.

19. Flooding caused by Hurricane Katrina in New Orleans, 2005

20. LEDC
Less economically developed country (LEDC) has low levels of
development, based on economic indicators, such as gross
domestic product (the country's income).
MEDC
A more economically developed country (MEDC) has high level
of development based on economic indicators such as gross
domestic product (the country's income).