Where do we get Tropical Storms & why?

Tropical Storms go by many different names in different parts of the world – but they are all low pressure areas with wind speeds of over 74 mph

and weather conditions that can cause huge damage.

Key features of Tropical Storms :

• They form over warm tropical oceans with temperatures of over 27 C

• They start in the Tropics – between the Tropic of Cancer (N) and Capricorn (S) but not on the equator

• Their path takes them westwards and then away from the equator either N or S

• They weaken over land

• They go by different names :

Hurricanes (Americas)

Cyclones (Indian Ocean)

Typhoons (Pacific Asia)

Willy Willy (Australia)

• They spin Clockwise in the S. Hemisphere

• & spin Anti-Clockwise in the N. Hemisphere

• They last 1-3 weeks before dying out

• Don’t mix them up with Tornadoes /Twisters

The main threats to life from tropical storms are

:

• Intense winds of 74 – 200 mph which cause trees

to break, bridges to collapse, destroy weaker

buildings and send debris flying through the air

which can kill anyone outside.

• A storm surge of higher-than-normal sea due to

the intense Low Pressure. With rising warm

moisture, air is rising, leading to less air pressure

on the sea surface – so it rises leading to sea water

flooding over low-lying coastal areas

• Intense waves that can shut down offshore oil-

rigs, capsize ships and cause destruction to coast

and port buildings.

• Very intense rainfall which can swell rivers and

lead to ‘fresh water’ flooding inland.

• Lightning destroys power lines, strikes oil tanks,

electrocutes people in puddles and starts fires.

What happens in a tropical storm ?

How do Tropical Storms form ?

The Saffir-Simpson scale is the main measurement of the intensity of hurricane. There are 5 categories of hurricane which

officially start when winds are over 74 mph. Below this there are ‘Tropical Storms’ and at the weakest level ‘Tropical

Depressions’.

Minimal : some branches broken off. Fencing blown

down. No real damage.

Moderate : Some trees blown down. Some damage to

mobile & other homes

Extensive : Weaker trees blown down. Mobile homes

wrecked. Roofs damaged

Extreme : Trees blown down. Mobile homes

destroyed. Wide building damage.

Catastrophic : Roofs blown off buildings. Extensive

building damage. Wide floods

The higher the Hurricane category, the stronger the winds, the

higher the Storm surge and the lower the pressure.

How are tropical storms measured ?

A tropical storm’s strength can change with

each day. A tropical storm can grow into a

Category 1 or higher hurricane if it passes over

warmer ocean – but if it passes over land it

might weaken down the scale again.

MEDC Case-Study – Katrina, New Orleans USA

Date & Location : August 28-30 2005 New Orleans, Gulf of Mexico, USA

Primary Effects : August 29th 2005

• Torrential Rain fell on the city, blocking storm drains and saturating the ground. Roads were flooded slowing down evacuation.

• 200 mph winds hit the coast – bringing down power lines and leaving 100,000 without electricity.

• A Storm Surge of 9m flooded in towards the low-lying city swamping the coastal areas and submerging houses. People escaped into

upper floors of houses, into roof spaces or onto roofs.

• 2 days after the hurricane, the steel levees which protected the lowest parts of the city gave way – causing 80% of the city to be

flooded to 6m in depth. Some of New Orleans is below sea level

Before Katrina hit : The hurricane grew from a Category 1 storm as it passed

over Florida but gained energy as it went over the warm waters of the Gulf of

Mexico at the height of summer. It became a Category 5 storm as it headed

towards New Orleans. People in the city were advised to evacuate and drive

inland on the 28th August. 90% of the inhabitants did – but 10% stayed behind

who were too poor, ill, elderly or excitement-junkies to leave New Orleans. That

left 50,000 people in the city.

Some people chose not to evacuate – as they had done so in previous

hurricane warnings, only to find the damage was far less than had been forecast

but their homes or shops were looted when they returned.

Both highways

were used for

cars evacuating

the city

Secondary Effects : August 29th - 31st 2005

Economic Secondary Effects :

• Chemical factory blaze occurs 4 days after the hurricane. Flood water causes short-circuit and sparks a fire. Maintenance crews had evacuated

the city.

As a result of this……. Toxic fumes covered parts of the city and the flood water was contaminated, slowing down rescue of survivors as this had

to be dealt with

• Thousands of businesses including factories, shops, offices and railways are destroyed by floodwaters and wind damage.

As a result of this…… Many thousands of people become unemployed and many who evacuated have no jobs to return to – so not all inhabitants

return.

As a result of this…..the city loses millions of dollars in business tax and income tax from paid employees. It has less money to deal with the

clear-up.

Social Secondary Effects :

• Thousands of survivors are left without food, water or medical supplies. Very little help comes in from outside in

the first 48 hours.

As a result of this…..some elderly survivors die in the sweltering August heat in the days after the hurricane,

others suffer as they don’t get their usual medication that they need for health conditions such as diabetes.

• 20,000 people make their way to the Superdome sports stadium on higher ground. Conditions become awful

with the heat, smell, no sanitation and very little food and water. As a result there’s much stress, tension and

anger

Political Secondary Effects :

• Some people start taking food and water from supermarkets. Others see this as ‘looting’ and threaten to shoot.

President Bush was criticised for not sending in emergency services quickly enough to establish law and order & help

survivors.

As a result of this….. The police shoot those they think are looting. A number of innocent people are shot dead by

police who mistakenly think they are looting.

In the months afterwards :

• The floodwaters were drained out of the city over the next 3 months.

• New, higher levees were put in place to protect the city from future storms

• Investment was put into rebuilding the city.

Katrina – the Follow-Up

In the days afterwards : Thousands of survivors were evacuated from New Orleans and dispersed amongst relatives, friends and people

with spare rooms across the USA. It is reckoned 80% of these people returned to New Orleans within 2 years – but others decided their

future lay elsewhere in the USA for good.

The Blame Game : Investigations were held to see who was most to blame for the Katrina disaster :

The flood engineers : they had built flood levees high enough to cope with Category 1-3 hurricanes. Katrina was a Category 4-5 and the levees

buckled in the face of higher seas than expected. Were they unprepared?

The weather forecasters : did they give the city enough warning? Did they warn the flood protection engineers that Category 1 or 2 storms would

give storm surges higher than the levees could cope with?

The city authorities : for not having evacuation plans for the poor, those without cars, the elderly and those reluctant to leave the city? They left

10,000 people in the city to face the hurricane. 1,863 of them died from it.

The residents : some chose to stay in the city, despite advice to evacuate. Should they blame themselves?

The President : for not getting help into New Orleans until 3 days after the hurricane? Some died in that time.

How can you prepare people for a Tropical Storm?

Years in Advance : On the coast of Bangladesh mangrove swamps have been planted. As they

grow they will absorb the impact of cyclones – the high storm waves and the storm surge before it

gets to settlements. A sort of vegetation ‘shock-absorber’.

Months in Advance : Storm shelters have been built in Bangladesh – one for every few

thousand villagers. When a tropical storm is forecast a villager goes round with a

megaphone warning people to go to the shelters. These are on higher ground, built of

concrete and on stilts to allow storm surges to flow underneath them.

Days in Advance : Better satellite monitoring and improved weather forecasting is helping

to identify developing storm systems. This should give people more warning. The important

thing is getting the forecast right – if people evacuate and there’s no danger, they will be

less likely to evacuate next time.

As the hurricane approaches : Those who choose to stay are advised to board up

windows and doors with wooden shutters. Evacuation warnings are given over TV

and radio and route ways are allocated to vehicles to leave the city. Finally, there

are emergency kits people should have ready with key essential like torches and

water purification tablets.

Scientists find it hard to agree what will be the pattern of Tropical Storms in the future. There are 3 main lines of thought :

1 Natural Cycle Theory : When you look at records of

hurricanes over the past 80 years there seems to be a

pattern of periods when there are more hurricanes, followed

by fewer, before there are more again. Some think this is

linked to the 22-year sun-spot cycle which means there are

times when the sun gives out more heat, and other times

there is less. Any increase in hurricanes would be seen as

entering one of the ‘rise’ phases in a natural cycle.2 Global Warming : Some experts think there will be

more tropical storms in the future due to man-made

climate change. The theory is that the CO2 we produce is

leading to a warming effect. This means oceans will be

warmer for longer and generate more Category 4-5

storms.

Global Warming

Warmer oceans

More evaporation of

ocean moisture

More intense low pressure from

rising moist air

More Hurricanes

3 Global Warming : Others predict a

warmer planet will lead to fewer

hurricanes. The logic is that as ice-caps

and glaciers melt they will put more cool

and fresh water into the oceans, reducing

ocean temperature and changing ocean

currents - which will mean fewer

hurricanes in the future – but maybe more

intense ones.

Global Warming

Cooler oceans

More melting of ice-

caps and glaciers

Less evaporation of

ocean moisture

Fewer Hurricanes

Future Pattern of Tropical Storms