1. What is the name of the meteorological phenomenon that means the same as all of these?
NASA
Hurricane 1
NASA
NOAA 3
Typhoon
Cyclone 2

2. Tropical Cyclones
21/09/2018
Learning Objectives:
What conditions lead to tropical cyclones?
In what way do they represent a hazard to people?

3. What are tropical cyclones? Where do they form?
What ingredients are required for their formation?

4. What is a tropical cyclone? Where does a tropical cyclone form?
A tropical cyclone is a low pressure system over tropical or sub-tropical waters, with organised convection (i.e. thunderstorm activity) and winds at low levels circulating either anti-clockwise (in the N.hemisphere) or clockwise (S.hemisphere). It has an average diameter of ~500km and height ~15km.
Where does a tropical cyclone form?
In the tropics!

5. What ingredients are required for their formation?
Warm water (>26.5oC)to a depth of at least 50m.
An existing atmospheric disturbance (e.g. a weak low pressure system)
Must be at least 500km (300miles) north or south of the equator so that the Coriolis force is strong enough to aid their development.
Small wind shear (only small change in wind speed throughout the atmosphere) so the developing system does not get ‘torn apart’.

6. What is the difference between a typhoon, hurricane and a cyclone?
The region in which they form

7. NOAA 4
World map showing the track of all known tropical cyclones. Note how none have formed in close proximity to the equator. Add the names of tropical cyclones in each region to your world map.

8. Naming conventions of tropical cyclones for world regions
"hurricane" (the North Atlantic Ocean, the Northeast Pacific Ocean east of the dateline, or the South Pacific Ocean east of 160E)
"typhoon" (the Northwest Pacific Ocean west of the dateline)
"severe tropical cyclone" (the Southwest Pacific Ocean west of 160E or Southeast Indian Ocean east of 90E)
"severe cyclonic storm" (the North Indian Ocean)
"tropical cyclone" (the Southwest Indian Ocean)

9. Severe tropical cyclone Hurricanes Severe cyclonic storm
NOAA 4
Severe tropical cyclone
Hurricanes
Severe cyclonic storm
Tropical cyclone
Typhoons

10. Date of storm formation in the Atlantic.
Worldwide Tropical Cyclone Statistics
14.9 hurricanes per year average
16.9 typhoons per year average
Date of storm formation in the Atlantic.
Named systems – Yellow
Hurricanes – Green
Category 3 or greater - Red 6 5

11. Tropical Cyclone Formation (Tropical Cyclogenesis)
NASA
This satellite image clearly shows the intertropical convergence zone (ITCZ). However it is broken into discrete clusters of thunderstorms. These are known as ‘waves’. Forecasters watch these areas for signs of tropical cyclogenesis. 7
NASA
ITCZ
Wave disturbance

12. Tropical cyclones originate from a humble thunderstorm!
These require converging air at the surface i.e. a low pressure system such as a wave on the ITCZ. These have anticlockwise winds (in the N.hemisphere) and so only form 500km either side of the equator (between 5o and 20o) where the Coriolis ‘force’ is strong enough.
NOAA - 8
Converging air in a low pressure forming thunderstorms

13. If a cold upper-level trough from mid-latitudes moves into the area of thunderstorm development then the air becomes convectively very unstable and the thunderstorms will start to grow very large.
Upper, cold low pressure
Warm, humid air
Warm sea

14. Diverging (moving apart) air aloft
As latent heat is released by the condensing water vapour, the cold air aloft warms and increases in pressure.
Diverging (moving apart) air aloft
High pressure
Low pressure
NWS - 9

15. Latent heat experiment
Bring 50ml of water to the boil. Time how long it takes for all of this water to evaporate.
The total amount of energy supplied to the water can be calculated from:
Energy = Time x 9800J/s
The latent heat of water can be found from:
L=Q/m
Where Q = Energy supplied and m= mass of water used in kg.

16. Latent heat experiment
You should find L=2.3million Joules/kg
This tells you how much heat energy is released when 1kg of water vapour condenses into liquid water in a tropical storm.
On average 1,000,000,000kg of water condense per second in a tropical cyclone.
Calculate how much energy is released per second in a tropical cyclone.

17. Answer: 2.3x1015 J/s
This amount of energy is the equivalent of a 10 megaton nuclear bomb exploding every 20 minutes!
A 10.4 Megaton nuclear bomb test
US Department of Energy - 10

18. The diverging air aloft ‘sucks’ air up from the surface and with continued convection causes the surface low pressure to drop further. Surface winds now increase and begin to spiral inwards. This make the sea rougher which makes the winds turn further to the centre of the developing storm. L
Blue arrows – Pressure gradient force (pgf)
Red arrows - Coriolis force
Black arrows – Direction of wind
As the surface friction increases, the wind slows and so the Coriolis ‘force’ decreases. The pgf remains constant and so the winds spiral into the centre of the surface low.

19. The feedback mechanism:
-Air now reaching centre is warm and moisture laden after travelling over choppy warm seas.
-This adds extra energy in the form of latent heat to the thunderstorms, increasing their rate of growth
The surface pressure drops further
Surface winds increase
Sea becomes more choppy
Extra warmth and moisture transferred to the air
And so on.
When knot wind speed is reached we call it a tropical storm and when it increases to 65 knots we call it a tropical cyclone.

20. Rearrange the statements to show the process of tropical cyclogenesis.
Task:
Rearrange the statements to show the process of tropical cyclogenesis. Or
Rearrange the pictures to show the stages of tropical cyclogenesis. Label them to provide an explanation of the processes involved.

21. Eye of storm = Calm light winds
>15km L
~500km

22. Eye – Centre of storm. Calm conditions
Eye – Centre of storm. Calm conditions. Surrounded by most violent winds up to ~200mph under the eye wall 11
NASA - 1
Hurricane Katrina
Hurricane Luis eye video satellite image
Picture taken by the NOAA Hurricane hunter aircraft
which monitors hurricanes which are threatening the US coast.

23. What factors stop the tropical growing to the size of the Earth!?

24. This growth will continue until:
Moisture is cut off – i.e. Cyclone moves over land
Heat is cut off – i.e. Cyclone moves too far north or south
Wind shear (wind strength increasing with height) increases – This tears the cyclone apart – Common near Hawaii. Video
Cyclone becomes ‘full’ of thunderstorms so latent heat release is limited.

25. How do tropical cyclones pose a danger to people?
NASA - 2

26. 90% of deaths in tropical cyclones are due to flooding.
1.) Storm surge (up to 5m) due to a) low pressure causing local rises in sea levels and b) wind pushing water along.
90% of deaths in tropical cyclones are due to flooding.
NASA - 12
Video
Relative effects of pressure surge and wind-driven surge.
Wikipedia - 13

27. Video of flying debris 2.) Wind damage 3.) Flying debris
4.) Damage to infrastructure e.g. Roads and electricity supplies.
Video of flying debris
FEMA News Photo - 14
Damage from Hurricane Katrina

28. What are the social, economic and environmental issues associated with tropical cyclones?

29. Disruption to all events e.g. School, work, sport
Social
Deaths & injuries
Disease
Disruption to all events
e.g. School, work, sport
Ensuing or deepened poverty
Economic
Cleanup bill
Damage to buildings & infrastructure
Loss of businesses
Loss of tourism 15
FEMA News Photo - Davie, Florida 2005

30. Destruction of habitats Sewage leaks Chemical leaks
New Orleans, Louisiana 2005
US Coast Guard - 16
Environmental
Destruction of habitats
Sewage leaks
Chemical leaks
US Coast Guard

31. Hurricanes are rated on the Saffir Simpson Scale – Link to official scale
Animation with interactive Saffir-Simpson Scale 17

32. Case Studies Hurricane Andrew: 24th August 1992 Bahamas & Florida
Category 5
Max average 1 min wind
speed = 175mph
Lowest pressure = 922mbar
Storm surge of 5.2m
67 deaths
$41.1 billion (adjusted to 2010 rates)
Over 1.1 million people evacuated and 1500 troops deployed to prevent looting.
Video
NOAA - 18

33. Case Studies Hurricane Mitch: 29th October 1998
Honduras, Nicaragua, Mexico,
Florida(flooding also in Central America)
Category 5
Max average 1 min wind
speed = 180mph
Lowest pressure = 905mbar
Storm surge of 3.7m in Honduras
11,000 deaths mainly in Central America due to flooding and mudslides – Up to 1500mm (5 feet) of rain fell!
$8 billion (adjusted to 2010 rates)
Honduras evacuated 45,00 people and put armed forces on standby. 100,000 later evacuated.
Video
NOAA - 19

34. Case Studies Hurricane Katrina: 29th August 2005
Bahamas, Florida Louisiana
Category 5 (3 at landfall in Louisiana)
Max average 1 min wind
speed = 175mph
Lowest pressure = 902mbar
Storm surge of 4.3m in Louisiana
1836 deaths
$90.1 billion (adjusted to 2010 rates)
State of emergency declared two days in advance. Unprecedented text used in weather statement to convey likely devastation of storm. 1.2 million people ordered to leave homes.
Video
NOAA - 20

35. Case Studies Super Typhoon Saomai: 10th August 2006
Zhejiang Province, China
Category 5 (4 at landfall)
Max average 1 min wind
speed = 160mph
Lowest pressure = 925mbar
Storm surge of 4.0m
458 deaths
$2.7 billion (adjusted to 2010 rates)
50,000 houses destroyed; 380 km2 of farmland flooded.
1.6 million people evacuated. 20,000 soldiers deployed to help in the cleanup and rescue efforts.
Video
NOAA - 21

36. Case Studies Cyclone Larry: 20th March 2006 Queensland, Australia.
NASA
Cyclone Larry:
20th March 2006
Queensland, Australia.
Category 5 (4 at landfall)
Max average 1 min wind
speed = 135mph
Lowest pressure = 940mbar
Storm surge of 2.3m
1 indirect death
$920 million (adjusted to 2010 rates)
Most banana crops destroyed, many houses in the direct path were damaged (including 99% in Silkwood).
Video

37. Meteorological statistics Preparations Impacts
Homework – Due
Research two tropical cyclones in different parts of the world, gathering data on:
Meteorological statistics
Preparations
Impacts
Responses to the cyclone including rebuilding plans and progress.
Extension
-Discuss how future development planning could incorporate tropical storm preparedness designs.
- OR argue whether we should continue building in these areas at all.

38. Role play! A major hurricane is heading towards the southern coast of the US where you live. Act as if you were:
-Meteorologist advising authorities
-Governor of state
-Emergency services on the ground
-Homeowner
-Business owner
-Storm chaser!
Imagine the views you would have as each of these characters and how you would argue your case.

39. Sources:
NOAA -
Image Science and Analysis Laboratory, NASA-Johnson Space Center. "The Gateway to Astronaut Photography of Earth”.
NOAA -
Wikipedia Commons -
NHC NOAA -
NHC NOAA -
NASA -

40. Sources:
NWS -
NWS -
US Department of Energy -
NOAA -
NASA -
Emmanuel.boutet – Wikipedia -

41. Sources:
FEMA News Photo -
FEMA News Photo -
US Coast Guard -
Wikipedia
NOAA-
NOAA -

42. Sources:
NOAA -
NOAA -
NASA -