More HazardsMore Hazards

Tropical storms

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Tropical storms have names in Tropical storms have names in different placesdifferent places

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Here is a hurricaneHere is a hurricane

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Look at these to get the idea of how Look at these to get the idea of how they formthey form

•http://www.ucar.edu/news/features/hurricanes/inside_the_storm.html

•And

•http://news.bbc.co.uk/1/hi/sci/tech/4588149.stm

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• Hurricanes all start over the sea where, for reasons that we do not fully understand, a patch of ocean has a surface temperature of more than 260C.

• This generally happens between 50 and 200 of latitude.

• The hot air rises taking a lot of water vapour with it. As the water vapour rises up it cools to form big cumulus clouds. This creates very low pressure at sea level. Wherever you have low pressure, air with higher pressure tends to move in to replace it.

• The winds that travel around the Earth (called the Trade Winds) at this point are pulled in to fill the gap left by the rising air. But due to the turning effect of the earth, air does not move straight into a low pressure zone but whirls in around and towards it – just like the water going down the plug hole – for the same reason.

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• We have the hot air rising, the air coming in from outside and coming under the cloud in a spin, picking up more water vapour and spiralling upwards as it warms. This has 2 effects; the first is that the storm clouds begin to be pulled into a spin by the incoming wind. The second effect is that the spinning storm is pulled outward – leaving a low pressure funnel at the centre.

• Now way up high there is cold air which is under higher pressure so this is sinks down into the centre – at the bottom this begins to warm and gets pulled in to the warm spinning stormy mass, and so more cold air follows in after it.

• As everything is spinning faster and faster the storm begins to drift sideways because of the trade winds – in a westerly direction and away from the equator. So in the Northern Hemisphere this is NW.

• What is it the Southern hemisphere?

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• Not only that but this huge bundle of energy depresses the sea level under it, so there is a backup ridge of water all around it – this gives rise to surges both before and after the hurricane has passed.

• Provided they have available warm water and there is no wind high in the atmosphere, they will gather speed as they move.

• So the hurricane brings surges and high winds and heavy rain all together! This why they cause so many problems to the countries they cross.

• But once they meet landfall, the warmth from the warm water is no longer available and so the winds quickly slow down they pass over the coast. Also the very low pressure at their centre begins to rise, as the air is not ascending so fast. There will still be heavy rain clouds in the system but the devastating damage of high winds in excess of 120km per hour is less of the problem.

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This is typical of what happensThis is typical of what happens

• Note the direction of spin of the hurricane – this is in the northern hemisphere.

• Notice the variation in wind speeds – this too is typical.

• Notice where the storm surge has most impact – why do you think that is?

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So what is a category 1 Hurricanes So what is a category 1 Hurricanes like?like?

• 119-153 km winds internally.

• Storm surge 1.2 – 1.5m

• Minimal Damage on land

• Broken tree branches.

• Damage to trailers and mobile homes.

• Bent and broken signs.

• Some small boats torn away from their docks.

Photo of a damaged McDonald's Restaurant sign. Large pieces are missing from both the main sign section and

the golden arches above.

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So what is a category 2 Hurricanes So what is a category 2 Hurricanes like?like?

• 154–177 km winds internally.

• Storm surge 1.8 – 2.4m • Moderate Damage• Heavy damage to trees;

some trees knocked down.• Major damage to trailers

and mobile homes. • Some damage to roofs,

windows, and doors. • Heavy damage to piers and

marinas. • Many small boats torn

away from their dock

Photo of an overturned mobile home resting against the trunks of

several damaged and downed pine trees.

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So what is a category 3 Hurricanes So what is a category 3 Hurricanes like?like?

• 178–209 km winds internally.

• Storm surge 2.7–3.7m • Extensive Damage• Large trees knocked down.• Some mobile homes

destroyed. • Damage to roofs, windows,

doors, and small buildings. • Smaller buildings near the

shore destroyed. • Large buildings next to

shore damaged by waves. • Flooding near coast.

Photo showing a large section of a beach-front

hotel that has lost its foundation and totters

toward the sea.

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So what is a category 4 Hurricanes So what is a category 4 Hurricanes like?like?

• 210–249 km winds internally.

• Storm surge 4.0–5.5 m • Extreme Damage• All signs knocked down.• Severe damage to houses. • Mobile homes completely

destroyed. • Major damage to buildings

near shore. • Widespread flooding. • Major beach erosion.

Photo showing a residential neighbourhood that has

been heavily damaged by hurricane-spawned

tornados. Some houses are completely demolished,

while sections of bare walls remain standing where other houses used to be. Debris

litters the yards and streets.

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So what is a category 5 Hurricanes like?So what is a category 5 Hurricanes like?

• >250km/hour km winds internally.

• Storm surge > 5.5 m • Catastrophic Damage• Completely destroyed

roofs on many buildings. • Some buildings

completely destroyed. • Small buildings turned

over or blown away. • Very severe damage to

all buildings near the shore.

Two photos showing an apartment building before and after it was completely demolished by the

storm surge of Hurricane Camille. The before picture shows three buildings with a lawn, trees, and

parking lot. The after picture shows only rubble where the building

stood and bare trees.

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What we have been talking about is What we have been talking about is the effects of hurricanes, typhoons the effects of hurricanes, typhoons

or cyclonesor cyclones• Let’s look at a category 1 storm:

119-153 km winds internally. Storm surge 1.2 – 1.5m Minimal Damage on land Broken tree branches. Damage to trailers and mobile homes. Bent and broken signs. Some small boats torn away from their docks.

• These lead to some short term and maybe a few long term impacts on humans as a result of the storms.

• What might the short term impacts be? Can you think of any long term ones?

Put these in the impacts box in any order with a (L) or (S) after each one

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What we have been talking about is What we have been talking about is the effects of hurricanes, typhoons the effects of hurricanes, typhoons

or cyclonesor cyclones• Let’s look at a category 2 storm:

154–177 km winds internally. Storm surge 1.8 – 2.4m Moderate Damage Heavy damage to trees; some trees knocked down. Major damage to trailers and mobile homes. Some damage to roofs, windows, and doors. Heavy damage to piers and marinas. Many small boats torn away from their dock

• These effects could lead to some more short term and additional long term impacts on humans as a result of the storms. What do you think?

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What we have been talking about is What we have been talking about is the effects of hurricanes, typhoons the effects of hurricanes, typhoons

or cyclonesor cyclones• Let’s look at a category 3 storm:

178–209 km winds internally. Storm surge 2.7–3.7m Extensive Damage Large trees knocked down. Some mobile homes destroyed. Damage to roofs, windows, doors, and small buildings. Smaller buildings near the shore destroyed. Large buildings next to shore damaged by waves. Flooding near coast.

• These effects could lead to some more short term and additional long term impacts on humans as a result of the storms. What do you think?

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What we have been talking about is What we have been talking about is the effects of hurricanes, typhoons the effects of hurricanes, typhoons

or cyclonesor cyclones• Let’s look at a category 4 storm:

210–249 km winds internally. Storm surge 4.0–5.5 m Extreme Damage All signs knocked down. Severe damage to houses. Mobile homes completely destroyed. Major damage to buildings near shore. Widespread flooding. Major beach erosion.

• These effects could lead to some more short term and additional long term impacts on humans as a result of the storms. What do you think?

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What we have been talking about is What we have been talking about is the effects of hurricanes, typhoons the effects of hurricanes, typhoons

or cyclonesor cyclones• Let’s look at a category 5 storm:

>250km/hour km winds internally. Storm surge > 5.5 m Catastrophic Damage Completely destroyed roofs on many buildings. Some buildings completely destroyed. Small buildings turned over or blown away. Very severe damage to all buildings near the shore.

• These effects could lead to some more short term and additional long term impacts on humans as a result of the storms. What do you think?

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So now have looked at some of the So now have looked at some of the possible impactspossible impacts

•Same hurricane – different places?

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Same natural forces affect different Same natural forces affect different areas in a variety of waysareas in a variety of ways

•Now, we are going to think about how those impacts vary between LICs and HICs.

•For homework you are going to find out about the impact of a couple of recent hurricanes – one from an LIC and one from an HIC to see if our ideas support what really happens.

•To the whiteboard for the ideas we collected.