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• Tropical cyclones
• Cyclone Nargis• Typhoon Vamei
Dr Adam D. Switzer
Singapore NRF Fellow & Nanyang Assistant Professor - Principal Investigator, Tectonics Group
Earth Observatory of Singapore | NTU N2-01A-04 Tel: (65) 6592-1762 Email: [email protected]
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Coastal hazards II – Lecture objectives
At the end of this lecture you should be able to:
• Describe where tropical cyclones and mid latitude storms occur andwhy?
• Understand the difference between a storm and a cyclone.
• Explain with examples the saffir-simpson scale
• Comprehend the coriolis affect and how it relates to storms and
cyclones• Review Cyclone Nargis and the damage caused
• Understand the genesis of typhoon Vamei and why that storm isscientifically important.
Lakey, Sumbawa
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Areas at Risk
• Northern hemisphere tropical cyclones:
– Rotate counterclockwise, track clockwise• Southern hemisphere tropical cyclones:
– Rotate clockwise, track counterclockwise
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Tropical cyclones
• Tropical cyclones are also called Typhoons or Hurricanes
• Generally they form where water temperatures are above 26degrees in temperature.
• They are driven by the release of large amounts of latent heat which
occurs when moist air is carried upwards and water vapor condenses.
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Hurricanes, Typhoons and Cyclones
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Figure 6.7
• Pressure gradient:
high pressure low
pressure
• Pressure differences exist
due to unequal heating of
Earth’s surface
• Spacing between isobarsindicates intensity of
gradient
• Airflow is perpendicular to
isobars
Air pressure
gradients on
earths surface
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• Large low pressure
cells are cyclones,(high pressure cellsanticyclones)
• Air driven towardsthe centre of acyclone due topressure gradientsgets deflected by
Coriolis to spiralaround the centre.
Cyclones
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Coriolis effect on a rotating platform, as one person throws a ball to another person.
Freely moving objects on the surface of the Earth experience a
Coriolis force, and appear to veer to the right in the northernhemisphere, and to the left in the southern hemisphere.
Coriolis affect
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• A cyclone has convergence near ground but divergence atupper level.
• An Anticyclone has divergence near ground, convergence atupper level.
Converge and divergence
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Formation of Cyclones• Rising air and condensation can
build up into convective ‘chimney’of thunderstorms• Convection may strengthen when
air rises to high elevations withoutstrong winds to shear off anddissipate storms
• Begin to develop over warmseawater (26°C), between 5 and20 degrees latitude
• Vertical wind shear must beminimal
• Becomes cyclone force when windsexceed sustained velocity of 119km/hr
• Highest wind speeds exist alongedge of eye wall
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Formation of Cyclones
• Warm, moist air rises and spreads
at top of chimney• Warm air expands, cools andreleases latent heat
• Eye of cyclone can be as much as20oC warmer than surrounding air
• Rising air pulls more air into
center of cyclone at low elevations• Storm may be from 160 to more
than 800 km in diameter• Forward motion averages 25
km/hr
• Wind speed and pressure dropabruptly in the eye.
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Pressure and winds
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Saffir-Simpson Hurricane Scale
– Based on barometric pressure and average wind speed
– Lower barometric pressure, stronger cyclone – Lower-category storms can do almost as much damage ashigher-category storms
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Storm damage and deaths
• Global Costs related to cylcones have dramatically increased
– Rapidly growing populations along coast – More development in unsuitable locations
– More expensive buildings
• Number of deaths has decreased
– Improved ability to predict landfall locations – Coordinated ability to evacuate populations at risk
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Tropical cyclones
World wide tropical cyclone tracks from 1985 to 2005.
Singapore
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1000
TropicalDepression
9981008
Tropical Storm
1008
998
988978
Tropical cyclone
Pressure and winds
Intensity series
Formation and
anatomy of a
tropical cyclone
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Water piling against the coast
Wind waves
Low pressure dome
Normal tidalrange
What is storm surge?
Water accumulates against the coast
Strong winds cause large short period waves
Low pressure at the surface causes a dome of water
Storm surge
Storm surge
Coast
Ocean
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Case study - Cyclone Nargis
United States Department of State
Oth t i th i
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Other events in the region
Tropical cyclone Nargis made
landfall on 2 May 2008,
causing the worst natural
disaster in Myanmar's
recorded history.
Official death toll estimates
exceed 138,000 making it theeighth deadliest cyclone ever
recorded worldwide.
The 1970 Bhola cyclone,
caused up to 500,000
fatalities.
Fritz et al., 2009
Nature Geosciences
C l N i 27 J l 3 M 2008
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Hong Kong
Cyclone
Nargis’ path
Cyclone Nargis – 27 July - 3 May 2008
Tropical cyclone tracks from 1985 to 2005.
Singapore
Ti li t di t
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Timeline to disaster
April 27 - the India
Meteorological Department
(IMD) classified the systemas a tropical depression
IMD upgrade it to cyclonic
storm Nargis.
April 28 - Nargis is nearlystationary and intensifying.
That day the Joint Typhoon
Warning Centre (JTWC)
upgraded the storm tocyclone status.
Ti li t di t
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Timeline to disaster
April 29 - JTWC estimated
Nargis reached winds of 160
km/h. IMD forecast landfallin Bangladesh or
southeastern India. Cyclone
becomes disorganized,
weakened and heads
northeast.
April 30 – cyclone intensifies
and heads to the east before
turning northeast on May 1
Timeline to disaster
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Timeline to disaster
May 1 - Cyclone Nargis beganrapidly intensifying, due to thearrival of a new weather front.
May 2 - JTWC estimates thecyclone reached peak winds of 215 km/h (135 mph) as itapproached the coast of
Myanmar
May 1, 2008, visible image
from NASA's Atmospheric
Infrared Sounder
instrument on NASA's
Aqua spacecraft
H
Changes in intensity
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Changes in intensity
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Landfall and storm surge
May 2 - Cyclone Nargiscrossed the coast of
Myanmar with winds in
excess of 150km/hr, strong
waves and a storm surge
possibly up to 8m.
Researchers from the
University of Maryland
suggest that Cyclone Nargis
flooded about 14,402 km2 in
the Irrawaddy River Delta.
Gulf of
Martaban
Storm surge damage from Cyclone Nargis
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Storm surge damage from Cyclone Nargis
Fritz et al., 2009
Nature Geosciences
Flooding and
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Flooding and
destruction
The United Nations
estimated in its report that1.5 million people were
"severely affected" by this
cyclone.
The storm has killed 77,738
people and left 55,917
others missing and 19,359
injured, according to the
official death toll from the
United Nations.
Flooding and
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This small village waslocated about 27 km south
of Yangon, the country’s
largest city.
After the disaster, the trees
and buildings are
completely gone, replaced
by messy piles of rubble.
The fields are largely
submerged under brown
and green floodwater.
Flooding and
destruction
Flooded fields
Destroyed
villages
Ruined
infrastructure
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Typhoon (tropical storm) Vamei
Singapore
The belt 300 kilometers either
side of the equator has been
considered tropical cyclone-
free… well.. Until Dec 27 2001?
Vamei brought flooding and landslides to
eastern Malaysia, causing US$3.6 million in
damage and five deaths.
December 27 2001 in the South China Sea 1 5 degrees N about 150km north of
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December 27, 2001, in the South China Sea, 1.5 degrees N, about 150km, north ofthe Equator weather forecasters note the appearance of Typhoon Vamei.
Analysis later revealed that a weak, quasi-stagnant disturbance off Borneo interactedwith a strong, cold surge off Asia that set up a background rotation when it hit the
island. When the surge met the local disturbance, spin happened, and a typhoonrapidly emerged causing strong winds in both hemispheres..
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