9.3. Hurricanes

Question 1

Tropical Storms

Answer 1

A tropical storm is a low-pressure system up to 600km in diameter with wind speeds of up to 300km/h (typically
160km/h) and bringing up to 30–50cm of rainfall.
- a generic term that includes hurricanes (North Atlantic),
cyclones (Indian Ocean and the Bay of Bengal) and typhoons (Japan).

Question 2

Types of Tropical Storms

Answer 2

1) Hurricanes
2) Cyclones
3) Typhoons

Question 3

Hurricanes

Answer 3

Tropical storms in the Pacific and Carribbean Sea

Question 4

Cyclones

Answer 4

Tropical storms in the Indian Ocean

Question 5

Typhoons

Answer 5

Tropical storms in the South China Sea

Question 6

Tropical Storm Features

Answer 6

1) Eye
2) Eyewall
3) Rainbands

Question 7

Conditions for formation of Tropical Storms

Answer 7

• Sea temperatures over 27 degrees celsius to a depth of 60m (warm water gives off large quantities of heat when it is condensed - this is the heat which drives the tropical storm)
• Low-pressure area has to be far enough away from the equator so that the Coriolis force (force caused by rotation of the Earth) creates sufficient rotation in the rising air mass

Question 8

Saffir-Simpson scale description

Answer 8

• 1 to 5 scale based on a hurricane’s sustained wind speed
• the scale estimates potential property damage
• tropical storms with category 3 and higher are considered major tropical storms because of their potential for significant loss of life and damage

Question 9

Category 1 on Saffir-Simpson scale

Answer 9

• Winds 119-153 km/h
• Storm surge generally 1.2-1.5 km above normal
• No real damage to building structures

Question 10

Category 3 on Saffir-Simpson scale

Answer 10

• Winds 178-209 km/h
• Storm surge generally 2.7-3.6 km above normal
• Some structural damage to small residences and utility buildings
• Mobile homes destroyed

Question 11

Category 5 on Saffir-Simpson scale

Answer 11

• Winds greater than 249 km/h
• Storm surge generally greater than 5.5 km above normal
• Complete roof failure on many residences and industrial buildings
• Some complete building failures

Question 12

Eye of a storm

Answer 12

• centre of the storm
• very low pressure, with calm air (Coriolis Effect) spins the cloud away from the centre
• 20-40 miles across
• no rain

Question 13

Eyewall of a storm

Answer 13

• dense wall of thunderstorms surrounding the eye has the strongest winds within the storm
• changes in the structure of the eye and eyewall can cause changes in the wind speed, which is an indicator of the storm’s intensity
• the eye can grow or shrink in size, and double eyewalls can form

Question 14

Spiral Rainbands of a Storm

Answer 14

• storm’s outer rainbands can extend a few hundred miles from the centre
• Spiral clockwise in the southern hemisphere. Spiral anticlockwise in the northern hemisphere

Question 15

Hazards of Tropical Storms

Answer 15

1) High Winds
2) Storm Surges and Coastal Flooding
3) Intense Rainfall
4) Mass Movement

Question 16

Storm surges and Coastal Flooding

Answer 16

• greatest potential threat to life and property associated with tropical storms
• strong winds drive the surge, which rises in shallow water and pushes inland, causing flooding
• the highest part of the surge is where the strongest winds are
• the lower atmospheric pressure the higher the surge because air rises in low pressure systems, taking weight off the sea surface, allowing it to rise

Question 17

Intense Rainfall

Answer 17

• places crossed by the eye of a tropical storm experience two bands of intense rainfall from the cumulonimbus clouds around the eye
• This causes severe river flooding and mass movements, especially if the system is slow moving

Question 18

Processes in the Formation of tropical cyclones

Answer 18

1) Heated, very moist air rising from the ocean creates low pressure at the surface
2) More warm, moist air moves in over the ocean to replace the air that has risen
3) The spiraling mass rises rapidly
4) Thick Cumulonimbus clouds are produced from which heavy rain falls. The tropical spins due to the coriolis effect
5) The air cools at high levels and sinks, forming the eye of the storm

Question 19

Preparing for Tropical Storms

Answer 19

1) Risk assessment
2) Land use zoning
3) Reducing vulnerability of structures and infrastructures

Question 20

Risk assessment in Preparing for Tropical Storms

Answer 20

Living in coastal areas increases the risk associated with tropical storms.
- The evaluation of risks of tropical storms can be shown in a hazard map.

These can be based upon:

• analysis of climatological records to determine how often cyclones have struck, their intensity and locations
• the history of winds speeds and frequencies, heights and locations of flooding and storm surges over a period of about 50–100 years

Question 21

Land-use Zoning in Preparing for Tropical Storms

Answer 21

The aim is to control land use so that the most important facilities are placed in the least vulnerable areas, including floodplains.

Question 22

Building Structure in Preparing for Tropical Storms

Answer 22

New buildings should be designed to be wind and water resistant.

• Communication and utility lines should be located away from the coastal area or installed underground.
• Improvement of building sites includes raising the ground level to protect against flooding and storm surges.
• Protective river embankments, levées and coastal dikes should be regularly inspected for breaches due to erosion.
• Improved vegetation cover helps to reduce the impact of soil erosion and landslides, and facilitates the absorption of rainfall to reduce flooding.

Question 23

Predicting and Monitoring Tropical Storms

Answer 23

• Coastal areas which are at risk are protected by warning systems
• Aims to monitor storm development and forecast their intensity and tracks to allow evacuation
• HICs are usually more protected due to their advanced resources, level of capital, technology and communication system
• Example: National Hurricane Centre - Miami, Florida

Question 24

National Hurricane Centre (Miami, Florida) Predicting and Monitoring Tropical Storms

Answer 24

1) Geostationary satellite
2) Weather aircrafts
3) Land-based radar
4) Sea-based buoys

Question 25

Geostationary satellites in Predicting and Monitoring Tropical Storms

Answer 25

- Identify the hurricane’s position, wind movement and the atmosphere temperature and moisture level - Moves with the Earth to monitor the area 24/7

Question 26

Weather aircrafts in Predicting and Monitoring Tropical Storms

Answer 26

- Meteorologist fly in planes with their instruments across the eyeballs + eye to collect barometric pressure and wind intensity

Question 27

Land-based radar in Predicting and Monitoring Tropical Storms

Answer 27

Meteorologist learn about the hurricane wind fields, rain intensity and storm movement

Question 28

Sea-based buoys in Predicting and Monitoring Tropical Storms

Answer 28

Collects data on ocean currents, waves and other important interactions between the sea and the atmosphere

Question 29

How the National Hurricane Centre uses their data to predict and monitor tropical storms

Answer 29

- Data is analysed and then entered into a computer-generated numerical prediction model - NHC bases its forecast on models from all around the world - The different models used data differently, using different equations to simulate how the atmospheric + oceanic conditions will and may change overtime - The foresters are experienced thus knowing which models perform better and how the biases can be corrected based on past performances - The models may also used to predict path 5 days or beyond forecast)

Question 30

Limitations of Hurricane Prediction

Answer 30

- Hurricane are generally a predictable hazard, because they can be clearly seen and tracked by radar + satellite and warnings can be issued - However, it is not always as straightforward - Prediction is not always successful because tropical storms can suddenly changes path and their speeds may vary - Where hurricanes will make landfall is not known until very near the time it actually happens. - Often times, there are unforeseen factors that may affect intensity - There is, in contrast, no doubt that these predictions have reduced the potential of death especially in HIC

Question 31

Tropical Storm (Hurricane) Prevention Methods

Answer 31

1) Nitrogen blast 2) Chemical firms 3) Deep water pumps 4) Cloud seeding

Question 32

Nitrogen blast in preventing tropical storms

Answer 32

Releasing liquid nitrogen which cools the hurricane

Question 33

Chemical firms in preventing tropical storms

Answer 33

- Dumping chemicals into the ocean surface,reducing evaporation - ↓ latent heat transfer = ↓ energy source for hurricane

Question 34

Deep water pumps in preventing tropical storms

Answer 34

- Cooling the upper ocean - A million water pumps deployed in the path of the hurricane drawing cool water to the surface - ↓ heat from ocean surface = ↓ energy source

Question 35

Cloud Seeding in preventing tropical storms

Answer 35

- Silver iodide was used to seed the storm outside the eye-wall clouds - This would produce rainfall (or crystallized water droplet) releasing latent heat that would expand the hurricane (reduce moisture) - This weakens the whole hurricane by reducing wind speeds by distributing winds over a larger areas - Not effective + expensive