Cyclone in Bangladesh

1. Composed by
H.M.A. Mahzuz
Assistant Professor (PhD Fellow),
Department of Civil and Environmental Engineering,
Shahjalal University of Science & Technology, Sylhet,
Bangladesh.
E-mail: mahzuz_211@ yahoo.com
Cyclone in Bangladesh
View as a Disaster

2. Outline of the Lecture:
1.Geographic position of Bangladesh
2.Why Bangladesh is Vulnerability to Cyclone
3.What is Cyclone? Its type?
4.Periods of Cyclone in Bangladesh
5.Some Historic Cyclone in Bangladesh
6. Impacts of some major Cyclone in Bangladesh
7) Impact of sea level rise/ Climate change

3. 1. Geographic position of Bangladesh

4. Key facts:
• Bangladesh is cyclone prone.
• The cyclones develop over the Bay of Bengal tracking west and
northwards.
• The warm waters of the Bay fuel the growth of the storm.
• The low lying delta lands of Bangladesh provide no protection
from the high winds and storm surges.
• Bangladesh also is affected by major cyclones, on average 16
times a decade.

5. About the Bay of Bengal
• The Bay of Bengal, the largest bay in the world, forms the
northeastern part of the Indian Ocean. Roughly triangular in shape, it
is bordered mostly by India and Sri Lanka to the west, Bangladesh to
the north, and Burma (Myanmar) and the Andaman and Nicobar
Islands to the east.
• The Bay of Bengal occupies an area of 2,172,000 km². A number of
large rivers – the Ganges and its distributaries such
as Padma and Hooghly, the Brahmaputra and its distributaries such
as Jamuna and Meghna, other rivers such as Irrawaddy
River, Godavari, Mahanadi, Krishna and Kaveri flow into the Bay of
Bengal.
• Among the important ports are Chennai, Chittagong, Kolkata,
Mongla, Paradip, Tuticorin, Visakhapatnam and Yangon.

6. Max. length 2,090 km (1,300 mi)
Max. width 1,610 km (1,000 mi)
Surface area 2,172,000 km2
(839,000 sq mi)
Average depth 2,600 m (8,500 ft)
Max. depth 4,694 m (15,400 ft)
Dimension of Bay of Bengal

7. Figure: Relative depth of different sea

8. 2. Why Bangladesh is Vulnerable to Cyclone
The five main latitude regions of the Earth's surface
comprise geographical zones, divided by the major circles of latitude.
The differences between them relate to climate. They are as follows:
1. The North Frigid Zone, north of the Arctic Circle
2. The North Temperate Zone, between the Arctic Circle and the Tropic
of Cancer
3. The Torrid Zone, between the Tropical Circles
4. The South Temperate Zone, between the Tropic of Capricorn and the
Antarctic Circle
5. The South Frigid Zone, south of the Antarctic Circle

9. Torrid Zone: In the Torrid Zone (or tropical Zone or Tropic) the Sun is
directly overhead at least once during the year. Geographically, the torrid zone
is defined by 23.5 degrees north latitude and 23.5 degrees south latitude.
The tropical zone contains the areas those are the hottest places on earth. Most
have a wet season and a dry season as opposed to the more typical cold and hot
seasons of the temperate zones. Most areas within the torrid zone receive plenty
of rainfall to promote lush vegetation growth with the aid of the sun directly
overhead. The temperature stays relatively uniform from day to night. Cloud
cover helps keep the temperature uniform throughout the day and through the
seasons. This very same cloud cover also promotes almost daily rainfall during
the wet season. When warm moist air rises and is coupled with ground heating
by the sun, this causes atmospheric disturbances resulting in thunderstorms.
Prevailing winds in the tropics tend to blow from east to west, often causing
deserts to be located on the western side of major continental masses.
Key fact: As Bangladesh is located in Torrid Zone, cyclone is a very common
feature here. Here it is named as tropical cyclone, which is always very
dangerous. It is known as hurricane in America, typhoon in japan and china.
The cyclones, which are out of Torrid Zone, are known as extra tropical
cyclones.

10. Breeding place
The Bay of Bengal is the breeding sea for tropical
cyclones. Most of the devastative cyclones in human history
formed in this bay.
Presence of the sun over the region during the periods
feeds the required sensible heat, the bay water
maintains the critical ocean temperature of 26-27°C
needed for cyclone generation, sustain and intensify.

11. Energy Cycle
Cyclones are influenced, greatly, by the underlying ocean
surface over which they form and travel. As long as cyclone
remains over warm water, the energy is limitless. Warm and
highly humid Equatorial and Maritime Tropical air spirals
inward towards the center of the low pressure to replace the
heated and rapidly ascending air. Ascending air releases heat
into the atmosphere cools and are condensed into cloud.
Since tropical cyclones are warm core, air from the core rises
up and cold air sinks down which converts heat energy to
potential energy and, thereafter, potential energy to kinetic
energy. However, prime energy source in the storm field is
the latent heat of condensation.
The Hazards
•heavy rain and associated flooding
•storm surges
•in mountainous areas can result in landslides.

14. Fig: Wind directions

15. Figure: Thermal convective circulation of a rotating earth.

16. Tropical cyclone basin in Torrid Zone
• Traditionally, areas of tropical cyclone formation are divided into
seven basins. An average of 86 tropical cyclones of tropical storm
intensity form annually worldwide, with 47 reaching
hurricane/typhoon strength, and 20 becoming intense tropical
cyclones (at least of Category 3 intensity).
• 1 .North Atlantic Ocean
• 2. Northeast Pacific Ocean
• 3 .Northwestern Pacific Ocean
• 4. North Indian Ocean
• 5 .South-West Indian Ocean
• 6. Australian region
• 7 .South Pacific Ocean

17. 4. North Indian Ocean:
This basin is divided into two areas by India: the Bay of Bengal
and the Arabian Sea, with the Bay of Bengal dominating (5 to 6
times more activity). Still, this basin is the most inactive
worldwide, with only 4 to 6 storms per year. This basin's season
has a double peak: one in April and May, before the onset of the
monsoon, and another in October and November, just after.
Although it is an inactive basin, the deadliest tropical cyclones in
the world have formed here, including the 1970 Bhola cyclone,
which killed 300,000 people. Nations affected include India,
Bangladesh, Sri Lanka, Thailand, Myanmar, and Pakistan. Rarely
do tropical cyclones that form in this basin affect the Arabian
Peninsula or Somalia; however, Cyclone Gonu caused heavy
damage in Oman on the peninsula in 2007.

18. RSMC=Regional Specialized Meteorological Center

19. File:North Indian Ocean cyclone tracks 1980-2005

20. Tracks of major cyclones that crossed the coast of Bangladesh during
the period 1960 2009‐

21. Paths of severe tropical cyclones in
Bangladesh
Wind speed during the
major cyclones in
Bangladesh

22. Flood surge height during the
major cyclones in Bangladesh
Maximum radius of major
cyclones

23. Number of death of people and damages of severe cyclonic storms in
Bangladesh

24. . What is Cyclone? Its type?
Definition of Cyclone
The word cyclone comes from the Greek word Cyclos which means
coil of snake.
A cyclone an atmospheric system characterized by the rapid inward
circulation of air masses about a low-pressure center, usually
accompanied by stormy often destructive weather".
Scientific analysis defines cyclone as a the area arisen from
depression, where excessive wind blows around the center ,
anticlockwise in northern hemisphere & clockwise in southern
hemisphere.
As Bangladesh is located in Torrid Zone, cyclone is a very common
feature here. Here it is named as tropical cyclone, which is always
very dangerous.
It is known as hurricane in America, typhoon in Japan and China.
The cyclones, which are out of Torrid Zone, are known as extra
tropical cyclones.

25. Cyclone is usually
generated in warm ocean
surface (above 26 C). The
start of a cyclone is when
air heated by the sun rises
very swiftly which creates
areas of very low air
pressure. As the warm air
rises it becomes loaded
with moisture which
condenses into huge
thunder clouds.

26. Cool air rushes in to fill
the void that is left, but
because of the consent
turning of the earth axis
the air is bent inwards
then spirals upwards with
great force.

27. The swirling wind
rotate faster and
faster, forming a
huge circle which
can be up to 2,000
km across.

28. At the centre of the storm is
a calm, cloudless area
called the eye where there no
rain and the winds are fairly
light.

29. As the cyclone
build up it
begins to move.
It is sustained by
a steady flow of
moist air.

30. The strongest
winds and heaviest
rains are found
towering around
clouds which
merge into a wall
about 20-30 km
from the storm’s
centre.

31. Winds around the
eye can reach speeds
of up to 200km/h and
a fully developed
cyclone pumps about
2 million tonnes of
air per second.

32. Full Maturity
If the ocean and atmosphere environment continues to be favorable the
cyclone may continue to intensify as it moves pole-ward (due to inertial
diffrence). The cloud system becomes more circular in shape and
develops a distinct eye. This is the severe cyclone stage where the
cyclone is at its most dangerous. Approximately half of the cyclones that
form progress to full maturity.
Decay
Tropical cyclones normally decay when they move into a less favourable
environment, either over land or the cooler waters in higher latitudes.
The rate of decay varies with the circumstances. A cyclone moving over
land normally dissipates rapidly due to loss of its energy source, namely
the warm ocean surface. However in northern Australia cyclones moving
inland are frequently observed to persist as rain depressions for a number
of days bringing widespread flood rains, and may even redevelop if they
move over the ocean once more.

33. Different Parts of a Cyclone

34. Another look of a cyclone!!!

35. The
picture is
a
simplifie
d model
of a
tropical
cyclone.
It has
been cut
in half to
show the
'eye' and
the
moveme
nt of air.
It also
shows

36. The ideal
wind and
cloud
distribution
in a cyclone
is shown in
the figure.

37. •The graph shows typical variations (differences) in air pressure and
wind speed across a cyclone.
•The dotted lines indicate (air pressure). It starts at 1010 hPa
(hectopascals) and starts dropping as we move towards the eye of the
cyclone.
•It drops down to 950 hPa then increases as we move out of the eye.
both air pressure and wind speed drop in the eye of the cyclone.
•1 hecto-pascal (hPa) = 0.0145 psi

38. Figure: At USA Irene wind (light blue) and barometric pressure (violet)

39. Cyclones in the Bangladesh
CLASSIFICATION OF CYCLONE IN THE BAY OF BENGAL
i. The cyclonic disturbances over the North Indian Ocean as defined in the WMO Tropical Cyclone
Operational Plan for the region (TCP-21) are as follows:
In Bangladesh the
terms well marked low
and deep depression
are also used to
indicate cyclonic
disturbances with wind
speed between 17-21
kt (31-40 kph) and 27-
33 (51-61 kph)
respectively.
Types of Disturbances Corresponding Knots,
Kts
Wind Speed,
Kph
Low < 17 < 31
Depression 17-33 31-61
Cyclonic storm 34-47 62-88
Severe Cyclonic Storm 48-63 89-117
Severe Cyclonic storm
of hurricane intensity
>64 >118
Nomenclature Wind speed ranges
Kts Kph
Low Pressure Area >17 >31
Depression 17-27 31-50
Deep Depression 28-33 51-61
Cyclonic Storm 34-47 62-88
Severe Cyclonic Storm 48-63 89-117
Very Severe Cyclonic Storm 64-119 118-220
Super Cyclonic Storm >120 >221
ii. The Nomenclature of the Tropical
disturbances have been changed in the
26th Session of WMO/ESCAP Panel on
Tropical cyclone meeting held in
Maldives during February, 1999 as
follows:
1 knot - 1.85 km per hour

40. Cyclone Category
Wind Speed in
Km/h
Damage Capacity
01 120-150 Minimal
02 150-180 Moderate
03 180-210 Extensive
04 210-250 Extreme
05 250 and above Catastrophic

41. Tropical Cyclone Classifications [23][24]
The
Beaufort
scale
1-minute sustained winds 10-minute sustained winds
NE Pacific
&
N Atlantic
NHC/CPH
C
NW
Pacific
JTWC
NW Pacific
JMA
N Indian Ocean
IMD
SW Indian Ocean
MF
Australia & S
Pacific
BOM/FMS[4]
0–7
<32 knots (37 mph;
59 km/h)
<28 knots (32 mph; 52 km/h)
Tropical
Depression
Tropical
Depressio
n Tropical
Depression
Depression
Zone of Disturbed
Weather Tropical
Disturbance
Tropical
Depression
Tropical Low
7 33 knots (38 mph; 61 km/h)
28–29 knots (32–33 mph; 52–
54 km/h)
Deep Depression
Tropical
Disturbance
8
34–37 knots (39–43 mph;
63–69 km/h)
30–33 knots (35–38 mph; 56–
61 km/h)
Tropical
Storm
Tropical
Storm
Tropical
Depression
9-10
38–54 knots (44–62 mph;
70–100 km/h)
34–47 knots (39–54 mph; 63–
87 km/h)
Tropical Storm Cyclonic Storm
Moderate Tropical
Storm
Category 1
tropical cyclone
11
55–63 knots (63–72 mph;
102–117 km/h)
48–55 knots (55–63 mph; 89–
102 km/h) Severe Tropical
Storm
Severe Cyclonic
Storm
Severe Tropical
Storm
Category 2
tropical cyclone
12+
64–71 knots (74–82 mph;
119–131 km/h)
56–63 knots (64–72 mph; 104–
117 km/h) Category 1
hurricane
Typhoon
72–82 knots (83–94 mph;
133–152 km/h)
64–72 knots (74–83 mph; 119–
133 km/h)
Typhoon
Very Severe
Cyclonic Storm
Tropical Cyclone
Category 3 severe
tropical cyclone
83–95 knots (96–109 mph;
154–176 km/h)
73–83 knots (84–96 mph; 135–
154 km/h)
Category 2
hurricane
96–97 knots (110–
112 mph; 178–180 km/h)
84–85 knots (97–98 mph; 156–
157 km/h) Category 3
Hurricane98–112 knots (113–
129 mph; 181–207 km/h)
86–98 knots (99–113 mph; 159–
181 km/h)
Intense Tropical
Cyclone
Category 4 severe
tropical cyclone113–122 knots (130–
140 mph; 209–226 km/h)
99–107 knots (114–123 mph; 183–
198 km/h)
Category 4
hurricane
123–129 knots (142–
148 mph; 228–239 km/h)
108–113 knots (124–130 mph; 200–
209 km/h)
Category 5 severe
tropical cyclone
130–136 knots (150–
157 mph; 240–252 km/h)
114–119 knots (131–137 mph; 211–
220 km/h) Super
Typhoon
Super Cyclonic
Storm
Very Intense
Tropical Cyclone>137 knots (158 mph;
254 km/h)
>120 knots (140 mph; 220 km/h)
Category 5
hurricane

42. Areas affected in Bangladesh by Cyclone:
Coastal area:
Barisal, Pirojepur, Jhalkathi, Potuakhali,
Bhola, Borguna, Chandpur, Feni,
Noakhali, Chittagong, Cox’s Bazaar.
On average, 13/14 tropical cyclones
develop in the Bay of Bengal region each
year and 4/5 cross the coast.

43. 4) Periods of Cyclone in Bangladesh
Time:
Seasonal
cyclones are
very common
in
Bangladesh:
1) Pre-
monsoon:
April-May
2) Post
monsoon:
October-
November

44. Cyclone
Name
Status Landfall Area Landfall
Date
PYARR Cyclonic Storm THE SYSTEM CROSSED THE ANDHRA PRADESH COAST NEAR KALINGAPATNAM, India 19.09.2005
BAAZ Cyclonic Storm WEAKENED INTO A WELL MARKED LOW PRESSURE AREA OVERSOUTHWEST BAYOF
BENGAL
02.12.2005
FANOOS Cyclonic Storm CROSSING THE COAST NEAR VEDARANYAM. India 10.12.2005
MALA VERY SEVERE CYCLONIC STORM CROSSED ARAKAN COAST ABOUT 100 KMSSOUTH OF SANDOWAY, Myanmar 29.04.2006
OGNI SEVERE CYCLONIC STORM CROSSED THE COAST BETWEEN BAPATIA AND ONGOLE, India 30.10.2006
AKASH Cyclonic Storm Crossed south Bangladesh coast close to south of Cox's Bazar 14.05.2007
SIDR VERY SEVERE CYCLONIC STORM Crossed Bangladesh coast near Baleshwar River 15.11.2007
NARGIS VERY SEVERE CYCLONIC STORM Crossed southwest coast of Myanmar 02.05.2008
RASHMI Cyclonic Storm Crossed Bangladesh coast nearKhepupara 26.10.2008
KHAIMUK Cyclonic Storm Crossed the south Andhra Pradesh coast close to the north of Kavali 15.11.2008
NISHA Cyclonic Storm crossed Tamilnadu coast north of Karaikal 27.11.2008
BIJLI Cyclonic Storm crossed the Bangladesh coast near Chittagong 17.04.2009
AILA Severe Cyclonic Storm Crossed the West Bengal coast close to east of Sagar Island 25.05.2009
WARD Cyclonic Storm crossed north Sri Lanka coast near Trincomalee 14.12.2009
LAILA Severe Cyclonic Storm Crossed Andhra Pradesh coast near Bapatla 20.05.2010
GIRI VERY SEVERE CYCLONIC STORM crossed Myanmar coasteast-southeast of Sittwe 22.10.2010
JAL Severe Cyclonic Storm Crossed north Tamilnadu and south Andhra Pradesh coast 07.11.2010
THANE VERY SEVERE CYCLONIC STORM crossed the Tamil Nadu coast close to south of Cuddalore 30.12.2011
NILAM Cyclonic Storm crossed north Tamilnadu coast near Mahabalipuram, south of Chennai 31.10.2012
MAHASEN Cyclonic Storm Crossed Bangladesh coast between Chittagong and Feni 16.05.2013
PHAILIN VERY SEVERE CYCLONIC STORM Odisha& adjoining north Andhra Pradesh coast near Gopalpur 12.10.2013
Named Cyclone over Bay of Bengal during 2005 – till date

45. 5. Some Historic Cyclone in Bangladesh

46. List of some of the recent major cyclones which made landfall along Bangladesh coast
SCS (H) = Severe cyclonic storm with Hurricane wind, SCS = Severe cyclonic storm, CS = Cyclonic storm
Sl. # Cyclone with date
Maximum
wind speed (kph)
Maximum height of storm
surge (ft)
Coast Death
1.
SCS (H)
November 1, 1876
The Great Backerganj
Cyclone
220 10 Backergonj
1,00,000
died later on
1, 00,000 by
epidemics.
2.
SCS (H)
September 24, 1919
Not available Not available Sunderban Cost 3,500
3.
SCS (H)
October 9-10,1960
129 6 -Noakhali 3,450
4.
SCS (H)
October 31, 1960
208 6.1 5,149
5.
SCS (H)
May 9, 1961
160 5 11,468 3,500
6.
SCS (H)
May 28-29,1963
200 6 North of 11,520
7.
SCS (H)
May 11-12,1965
161 4 Barisal-Noakhali 19,270
8.
SCS (H)
December 14-15,1965
209 3.4-3.7 Cox's Bazar 873
9.
SCS (H)
October 1, 1966
145 6.7 Noakhali-Chittagong 850
10.
SCS (H)
November 12,1970
222 10 3,00,000
11.
SCS (H)
October 31, 1960 SCS
161 3.7 20
12.
SCS (H)
May 24-25, 1985
154 4.3 4,264
13.
SCS (H)
November 29,1988
160 4.9 1,598
14.
SCS (H)
April 29,1991
225 6.1 1,38,000
15.
SCS (H)
April 29,1991
215 3.3 Teknaf-Cox's Bazar 188
16.
SCS (H)
May 19,1997
230 4.5 155
17.
SCS(H)
May 26, 1997
150 3.1 70
18.
CS(H)
Oct 28, 2000
115 2 61

47. Brief Description of Major cyclones in Bangladesh
April 29, 1991 :
•On the Saffer-Simpson hurricane scale this storm
ranked as a strong Category 4 with
•sustained up to 225 km/hr
•with a storm surge of 20 feet
•nearly 1 40,000 people died
•over 10 million became homeless
•The economic losses alone from the cyclone are
estimated at US$ 2.4 billion.

48. Satellite Image of The cyclone 1991 (Cobb 1993)

49. District No. of Deaths No. of Injured
Chittagong 79,697 2,600
Cox’s Bazar 51,147 133,500
Noakhali 8,878 995
Bhola 221 771
Patuakhali 20 105
Rangamati 12 381
Laxmipur 9 287
Barguna 7 112
Feni 5 -
Jhalakathi 1 12
Pirojpur 1 -
Chandpur 1 -
Bandarban 1 86
Total
140,000
138,849
District Wise Breakdown of Deaths and Injured by the 1991 Cyclone

51. Cyclone Of May 19, 1997:
The Complete Story Of Breeding &Development
•The cyclone was found to grow rapidly & the intensity
was estimated at the image of 17 May
•The image of 18 may showed that the St’ Martins island,
Cox’s Bazar & Teknaf area had already been hit by the
outer periphery of the cyclone
•The image of 19th May showed that the center of the
cyclone had just crossed the coast of Chittagong

58. Cyclone SIDR

59. Cyclone Sidr track and
landfall

60. What is a Storm Surge
Storm Surge Disasters in Bangladesh
Storm surges are oscillations of the water level in a coastal or inland
water body in periods ranging from a few minutes to a few days,
resulting from atmospheric forces in the weather system. A storm
surge is partly caused by pressure differences within a cyclonic
storm and partly by high winds acting directly on the water. This
results in a mass of water, a huge wave, moving at the same speed
as the cyclone. In the northern Bay of Bengal, a unique combination
of high tides, a funnelling coastal configuration, the low flat coastal
terrain, and a high population density have produced some of the
highest mortality figures associated with storm surges.

61. Storm Surge and Flooding
Storm surges are generated by two principal factors: pressure drop and wind
stress. Atmospheric pressure drop below normal raises the water through
"inverted barometer effect" (which is also called "sucking effect") by a nominal
amount, i.e. about 1 cm per 1 Mb drop of pressure. Wind is the main force for
the generation of storm surges. Wind exerts tangential as well as normal
(downward) stresses on the water underneath. Water being almost
incompressible, the normal stress cannot generate any noticeable motion in
water. The tangential stress generates long water waves or storm waves i.e.
storm surges. The amplitude of the wave depends directly on the strength of the
wind. The wind stress is approximately proportional to the square of the wind
speed.
Flooding by storm surge in Bangladesh can be classified as follows:
a) Normal coastal flooding - no damage on crops,
b) Moderate coastal flooding - very limited damage on crops,
c) Moderately high coastal flooding - high damage on crops but relatively low
damage on properties and lives,
d) High coastal flooding - large scale damage on crops, properties and lives,
e) Severe coastal flooding - severe damage on crops, properties and lives.

62. Typical Storm
Surge Inundation
Characteristics
for cyclones of
Varying Strength
in Bangladesh.

63. The reasons for large impact of storm surges on the coast of
Bangladesh are the following.
(1) The phenomenon of recurvature of tropical cyclones in the Bay
of Bengal,
(2) Shallow continental shelf, especially in the eastern part of
Bangladesh,
(3) High tidal range,
(4) Triangular shape at the head of the Bay of Bengal,
(5) Almost sea-level orography of the Bangladesh coastal land,
(6) High density of population and coastal defence system.

64. Coastal region Surge height at the Sea Coast, hT
(m)
T= 50-year T = 100-year
Tekhnaf to Cox’s Bazar 4.5 5.8
Chakaria to Anwara, &Maheshkhali-kutubdia 7.1 8.6
Chittagong to Noakhali 7.9 9.6
Sandwip, Hatiya & all islands in this region 7.9 9.6
Bhola to Barguna 6.2 7.7
Sarankhola To Shyamnagar
5.3 6.4
Table: Design surge heights at the sea coast, hT

65. 7) Impact of sea level rise/ Climate change
Climate change may
result in Temperature
rise. This may
increase the melting of
ace caps resulting in
sea level rise.
Intergovernmental Panel on
Climate Change (IPCC)

66. IPCC estimation

69. Ref: CU Sea Level Research Group, University of Colorado

70. Low elevation of coastal
communities (LECZ)
The average land
elevation is about 7.62
meters (25 ft.) above
mean sea level whereas
for coastal and
offshore island is about
1.5 meters (approx.)
above mean sea level
and as such major
portion of the
waterways are under
tidal influence.

71. Table-2: Sea level rise (SLR) in Bangladesh and its possible impacts

75. • Accelerated sea-level rise certainly will increase the
flooding and property damage triggered by tropical
cyclones.
• A future rise in sea level is far more certain, particularly
along the coastlines most prone to tropical cyclone
disruption. For example, a rise in sea level of 1 meter for
the New York City region would result in the present-day
100-year flood events occurring every 3 to 20 years.

76. FULL PAGE PICTURES OF CYCLONE

78. Thank you for your
kind concentration
78