11. Formation of Tropical Storms

Question 1

What are tropical storms?

Answer 1

Very intense areas of low pressure which creates huge storms with high winds, heavy rain and storm surges.

They are a natural weather phenomenon which can be expected in certain latitudes and at certain times of the year.

Question 2

What do tropical storms play an important role in?

Answer 2

Redistributing heat from the tropics towards the poles -> without them the global climate would be very different.

Question 3

What does cloud and rain do?

Answer 3

Extend in a series of waves from the eye wall

Question 4

Where is the most powerful part of the storm?

Answer 4

The bank of cloud that circles the central eye -> this is where the winds are most devastating

Question 5

What do fully formed mature tropical storms have?

Answer 5

A central eye around 10-15 kms in diameter -> the descending air creates calm, clear conditions with higher temps

Question 6

Stage 1

Answer 6

The sun warms the oceans to a critical 27 degrees Celsius

Question 7

Stage 2

Answer 7

This draws water vapour up from the ocean surface.
The warm air rises quickly under low pressure conditions.

Question 8

Stage 3

Answer 8

The rising air evaporates and condenses to form thunderstorm clouds. As the air condenses, it releases latent heat which powers the storm and draws up more water.

Question 9

Stage 4

Answer 9

Several smaller thunderstorms join together to form a giant spinning storm. When surface winds reach 74 mph, the storm officially becomes a tropical storm.

Question 10

Stage 5

Answer 10

The storm now develops an eye at its centre,
The outer edge of the eye is the eyewall where the most intense weather conditions (strong winds and heavy rain) are felt.

Question 11

Stage 6

Answer 11

The Coriolis effect causes the air to spin upwards around a central calm eye of the storm.
Cold air sinks in the eye, therefore there is no cloud, so it’s drier and much calmer.

Question 12

Stage 7

Answer 12

As the storm is carried across the ocean by the prevailing winds, it continues to gather strength.

Question 13

Stage 8

Answer 13

On reaching land, the storm’s energy supply (evaporated water) is cut off.
Friction with the land slows it down and it begins to weaken.
If the storm reaches warm seas after crossing the land, it may pick up strength again.

Question 14

What areas do tropical storms form?

Answer 14

Only form in areas between 5-30 degrees north and south of the equator where the high rates of insolation from the sun warm the oceans.

Question 15

When are tropical storms most common?

Answer 15

in Summer and Autumn when sea temps are highest

Question 16

What kind of wind do tropical storms need?

Answer 16

Need a low wind shear (wind that remains constant and doesn’t vary with height).
This allows tropical storm clouds to rise to high levels without being ripped apart.

Question 17

What sea temps do tropical storms form at?

Answer 17

Only form when sea temps are 26/27 degrees celsius and above depth of 70m.
This provides heat and moisture that causes warm air to rise rapidly, creating a deep area of low pressure. Latent heat is then released to power the storm.

Question 18

Why don’t tropical storms usually form on the equator?

Answer 18

The coriolis effect is too weak to allow storms to start spinning. The coriolis effect increases with distance from the equator.

Question 19

Where are tropical storms most likely to form?

Answer 19

Where there is atmospheric instability and warm air is forced to rise.
The Inter-Tropical Convergence Zone where 2 limbs of the Hadley Cell meet to form low pressure on the ground is a perfect place for tropical storms to form.

Question 20

What is used to classify tropical storms?

Answer 20

The Saffir-Simpson Scale
Based on sustained windspeeds and has 5 categories.

Question 21

What is the NOAA prediction based on?

Answer 21

• sea surface temps
• atmospheric conditions
• climate seasons such as El Nino and La Nina

Question 22

Can tropical storms be predicted?

Answer 22

To an extent they are predictable as they are restricted to the tropics and occur in Summer and Autumn

Question 23

Strong winds description

Answer 23

Tropical storms are powerful with average wind speeds in excess of 120km/h

Question 24

Cause of tropical storms

Answer 24

• A deep area of low pressure and the deeper the low pressure, the stronger the wind as bigger diffs.
• The bigger the pressure difference, the stronger the winds.

Question 25

Nature of the impacts from strong winds

Answer 25

• Capable of causing significant damage and disruption by tearing off roofs, breaking windows and damaging communication networks.
• Debris forms flying whisked up by wind
• Damaged power lines often lead to widespread electricity cuts and occasionally fires.

Question 26

Storm surge description

Answer 26

A rapid rise in sea level in which water is piled up against the coastline to a level far in excess of normal conditions at high tide.

Question 27

Cause of storm surges.

Answer 27

• These surges in sea water are caused by a combination of intense low air pressure which enables sea level to rise vertically together with.a powerful driving surface winds.
• Geography of coastline can influence the storm surge, gently sloping seabed increases height of surge.
• If the storm coincides with a high tide of the impacts can be even more devastating.
  -Rising sea levels from climate change may take storm surges more devastating.

Question 28

Nature of impacts from storm surge

Answer 28

• Storm surges can cause widespread damage and loss of life.
• The environmental impacts can be significant with agricultural land inundated with saltwater and debris.
• Freshwater supplies may be polluted.
• Coastal erosion can undermine and damage key infrastructure.

Question 29

Description of coastal and river flooding

Answer 29

Heavy rainfall that causes water to build up at high intensity.

Question 30

Cause of coastal and river flooding

Answer 30

• Warm humid air associated associated with a tropical storm can generate torrential rainfall, often in excess of 200m in just a few hrs which can trigger flooding at the coast.
• As a tropical storm moves inland, it gradually weakens as its moisture and energy supply is cut off.
• Urbanisation/ impermeable surfaces exacerbates flooding

Question 31

Nature of impacts of coastal and river flooding

Answer 31

• Evacuation of people
• Destroys infrastructure

Question 32

Description of landslides

Answer 32

When intense rainfall/ tropical storms weakens the land, causing it to slide

Question 33

Cause of landslides

Answer 33

• Up to 90% of landslides each year are caused by heavy rainfall, and many are triggered by tropical storms.
• Intense rainfall increases pore water pressure which weakens cohesion and triggers slope failure.
• Load release caused by tropical induced landslides may trigger earthquakes.

Question 34

Nature of impacts of landslides

Answer 34

• Landslides can cause earthquakes
• 1998, Hurricane Mitch, triggered multiple landslides that killed 18,000 people in Central America.