Cyclone and Storm Surge - Iczmpwb.org

4.12
work station (the Automated Tropical Cyclone Forecasting System, ATCF) is already in operation
at the Joint Typhoon Warning Centre, Guam for the past many years. The Australian Bureau of
Meteorological Research Centre, together with their Bureau of Severe Weather Programme Office has
also developed a work station based model for storm surge forecasting.
Mechanics of the Storm Surge
In the Bay of Bengal area itself 142 moderate to severe storm surge events are on record from 1582 to
1991. These surges, some in excess of eight meters (26 ft.), have killed hundreds of thousands of
people, primarily in Bangladesh (Murty and Flather, 1994). At least five processes can be involved in
altering tide levels during storms. These include the pressure effect, the direct wind effect, the effect of
the earth's rotation, the effect of waves, and the rainfall effect (Harris, 1963). The pressure effects of a
tropical cyclone will cause the water level in the open ocean to rise in regions of low pressure and fall in
regions of high pressure. Wind stresses causes a phenomenon referred to as "wind set-up”, which is the
tendency for water levels to increase at the downwind shore, and to decrease at the upwind shore that is
inversely proportional to depth. Wind set-up on an open coast will be driven into bays in the same way
as the astronomical tide.
Surge and wave heights on-shore are directly governed by the configuration and bathymetry of
the sea-bottom. For narrow shelf (one that drops steeply from the shoreline and subsequently produces
deep water in close proximity to shoreline) tends to produce a lower surge, but a surface wave of higher
magnitude. The situation is continental shelf region along the eastern belt of India is gently sloping and
quite wide compared with the west coast which results in higher surges along east coast compared to
the west coast. In deeper waters, a surge can be dispersed away from the cyclone. Upon entering a
shallow gently sloping shelf, the surge cannot be dispersed away, but is generally driven onshore by the
wind stress associated with the tropical cyclone. In the immediate vicinity of near-shore area, topography
of land surface is another important element in determining the storm surge extent. Areas where the land
areas like less than a few meters above mean sea-level are at particular risk from storm surge
inundation.
4.6. Bottom Characteristics in Bay of Bengal
The Bay of Bengal is the northward extended portion of the Indian Ocean. It is located between latitudes
5°N - 22°N and 80°E - 100°E longitudes. Westward it is bounded by the East coast of Sri Lanka and
India, on north by the deltaic region of the Ganges-Brahmaputra-Meghna river system, and on the east
by the Myanmar peninsula extended upto the Andaman-Nicobar ridges (Figure – 1). The southward
boundary of the Bay is approximately along the line drawn from Dondra Head in south of Sri Lanka to