Though the Tropical Cyclones/Hurricanes are classified on the wind speeds in kilometers per hour, Storm Surge are responsible for 90% of life losses and are truly devastating.
But what is a Storm Surge? The Storm Surge is a dome of sea water that sweeps over the coastline during the landfall of the Tropical Cyclone/Hurricane and the scale of the surge is about 100 to 200 kilometers at the landfall.
Strong onshore winds and low pressure at the center of the Tropical Cyclone/Hurricane are responsible for a Storm Surge. There is a half meter of surge for every 50 millibars of pressure loss in the center of the storm. So as storm intensifies the Storm Surge enhances.
The timing of the Storm Surge is very critical. If the surge occurs at the normal sea high tide, then the height of the surge is increased by the height of the normal sea high tide. Additionally the wind driven waves can range up to 3 feet and increase the penetration of sea water on land substantially.
The impact of the Storm Surge is dependent on the nature of the coastline. If there is a shallow slope of land from ocean to the coastline/community, the surge will penetrate substantially far inland. However if there is a deep sea and a high coast line, then it acts to block to the movement of the ocean water into the community itself.
India had fare share of the Storm Surge events:
Andhra Pradesh Cyclone of 1977 had a 5 meter storm surge and the sea water penetrated up to 12 kilometers in land. However there was low sea tide at the of the landfall of the Super Cyclone and hence the Storm Surge height & penetration inland was not to the full extent.
In Paradeep Super Cyclone of 1999, there was a Storm Surge with a height of about 5 to 6 meters. Coastal roads were filled up with sand dunes of 1 meter height and a half kilometer width. Fishing trawlers were thrown inland up to 2 kilometers.
In Rameshawram 1964 cyclone Danushkodi Island experienced Storm Surge of 5 to 6 meters and killed all the 120 passengers in the train. Also the famous Pamban Bridge was washed out completely by the Storm Surge.