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The tropics' deadly force
Storm surge is considered the most dangerous part of any tropical system
Last Modified: 01 Sep 2011 10:51
A McDonalds lies in ruins due to storm surge from Hurricane Katrina in 2005 [Getty]

When talking about tropical weather, one term that you may hear is "storm surge". Whether it is a hurricane, typhoon or cyclone, this coastal phenomenon will always be part of the tropical equation.

Along coastal communities where tropical systems threaten, storm surge is often the greatest threat to life and property. In 2005 Hurricane Katrina’s storm surge was responsible for 1500 deaths. In the country of Myanmar, Cyclone Nargis ripped through the low lying delta region in 2008 and is said to be blamed for over 135,000 deaths because of the abnormal surge of water rushing into the region.

So, what exactly is storm surge? It's the rise of water generated by a storm, which can cause extreme flooding in coastal areas. When you add on top of that the normal elevation of the water during high tide, then you have what is called "storm tide".

A storm surge is produced by water being pushed toward the shore by the force of the winds moving around the storm. How intense the storm surge will be depends on several factors; intensity, forward speed of the storm, size of the storm and characteristics of the coastline which is being affected.

When talking about the power of a storm surge, it's always better to over estimate its height rather than under estimate. In 2005 scientists learned a great deal about storm surge from Hurricane Katrina. At its strongest point, Katrina was at a maximum intensity of a category five, giving it an estimated storm surge height of over 5.7 metres. Just before landfall, it had weakened to a category four, with an expected surge height of 4 to 5.5 metres, but this is not what the Gulf Coast received. 

Even though Katrina had weakened before landfall, the churning waters hadn't. Add the higher astronomical tide at the time and you have the coastline of Mississippi receiving a storm surge of seven to eight metres, with some spots indicating higher because of debris left in the top of trees.

Another main factor that affects the power of the surge is the continental shelf close to shore. A shallow sloping shelf will potentially produce a greater storm surge, such as the region around the Gulf of Mexico.  While a steep continental shelf that drops off rather quickly will produce a lower storm surge.

Other geographical variables are also important to factor in to the size of the surge. Harbours, bays and estuaries are at higher risks for more intense storm surges because the water becomes confined and converges into a smaller area with no other place to go than onshore.

The power of the tropics and the strength of the storm surge will never be controlled. It is up to the individual and the community to educate themselves about their local hazards and to stay informed when any tropical system threatens.

Source:
Al Jazeera
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