How to Predict a Hurricane’s Damage


Wind, rain, and the raging sea can wreak havoc, but their effects vary widely. A hurricane with 135-MPH winds that crossed Texas in 1949, for example, caused two deaths, but it remained in rural areas, destroying crops but not cities. Hurricane Beulah, in 1967, produced winds gusting to more than 100 MPH in Texas, but of the 15 deaths, 10 were due to floods and 5 to the 155 tornadoes the hurricane triggered. Hugo, on the other hand, in 1989, was the most destructive hurricane in U.S. history. With winds gusting to 220 MPH over the Caribbean islands and more than 80 MPH over the United States, accompanied by storm surges and tornadoes, Hugo killed a total of 43 people and caused damage costing $10.5 billion in the United States, as well as destroying almost all the homes on several of the islands it crossed.

These are among the most devastating hurricanes ever recorded. Others produce far less destruction despite generating winds, rain, and waves that may be just as fierce. Clearly, when local communities find themselves in the path of an approaching tropical cyclone they need to know the scale of the destruction they can expect. Emergency services, too, can function much more efficiently if they are given advance warning of the type and extent of the incident with which they will have to deal. This need was recognized long ago and the first U.S. hurricane warning was issued in 1873, when a tropical cyclone was seen approaching the coast between New Jersey and Connecticut.

Hurricane's Damage

Potentially dangerous storms can now be tracked for much longer and in more detail as they form, intensify, and move over the ocean. At the same time their characteristics can be studied and their effects predicted. Much of the needed information is made available and adequate preparation can be made in time at least to minimize the number of casualties. The results have been dramatic. In 1925, hurricanes caused approximately 16 deaths for every million dollars of property damage. That number has been reduced drastically. For Camille, in 1969, there was one U.S. death for every $284 million of damage, and for both Gilbert in 1988 and Hugo in 1989, 1 death for every $2 billion of damage. (All damage costs are corrected for inflation and expressed in 1990 dollars.) Prediction allows time for life-saving preparation.

Although the ratio of deaths to property damage has improved and the actual number of deaths has decreased, the cost of hurricane damage to property in the United States has increased sharply during this century. An average of more than 800 people a year was killed by hurricanes between 1900 and 1910. By the 1990s the average was about 5. The cost of property damage, however, increased from almost nothing in the first years of the century to around $500 million a year in the 1930s and $2.6 billion in the 1990s. Improved precautionary measures account for the reduction in the number of deaths. The increasing risk to property is due to the rising popularity of Florida and the Gulf coast as places to live or vacation.

Measurements of the essential features of a tropical storm begin from the time it forms. At first they amount to an alert among meteorologists at the National Hurricane Center, in Miami, which is part of the National Oceanic and Atmospheric Administration (NOAA). When it appears that the storm is intensifying and heading for land, closer observation begins and the resources devoted to its study increase greatly as it approaches.

The atmospheric pressure in the center is monitored because from this the meteorologists can calculate the wind speed. Cloud formations are observed because this allows the intensity of the rainfall to be estimated. The temperature is also watched closely because it is its warm rather than cool center that distinguishes a hurricane from a tropical storm. It is also important to measure the size of the entire storm system. This determines the width of the area it will affect as it moves inland and also allows scientists to calculate wind speeds at varying distances from the center.

As these measurements and calculations are being made, the track of the storm is being plotted. This plot, together with knowledge of the prevailing winds outside the disturbance and experience of the behavior of past hurricanes, provide a basis for the future track to be predicted. Hurricanes can change course for no apparent reason, so there is an inevitable element of uncertainty in the predicted track. To allow for this, warnings are issued for a belt considerably wider than the hurricane itself.

At this stage the meteorologists know the size and strength of the hurricane and have predicted where it will cross the coast, and from measurements of its speed, when it will arrive. Now other considerations become important. The pressure in the eye tells them by how much the sea will rise, and its time of arrival must be related to the state of the tide to anticipate the total rise in sea level. The size of sea waves can be calculated from knowledge of the wind speeds and must be related to the shape of the coast and slope of the sea bed. Together, the rise in sea level due to pressure, the tide, and the growth in the size of waves as they approach the shore make it possible to predict the size of any storm surges. The elevation of land behind the shore determines the distance the storm surges will penetrate inland, and when account is taken of the effect of the rainfall on natural drainage systems it becomes possible to predict the severity of any flooding.

Hurricanes are graded according to their eye pressure, wind speeds, and height of their storm surges, usually on the Saffir/Simpson scale of 1 to 5 . It is now possible to assign the hurricane to a category and it is its category that determines the precautionary measures that should be taken before it arrives. The Saffir/Simpson category indicates the kind and extent of the damage the storm will cause, but only in general terms. Obviously, a hurricane that moves across a city center will cause far more damage than one passing only across sparsely populated countryside. No monetary values are attached to damage predictions, of course. Those come after the storm has passed and are based on valuations made by insurance companies. Warnings in advance of the storm are of such things as “mobile homes destroyed,” “flooding to 6 miles inland,” or “extensive damage to roofs.” They are meant to suggest degrees of severity without being specific.

Typically, the first “hurricane watch” warning, issued one or two days before the storm is forecast to arrive, affects a belt of coast and its hinterland about six times wider than the diameter of the hurricane. Much of this belt, to either side of the hurricane center, will miss the full force of the storm, although it may still experience strong gales. Because predictions of hurricane behavior are imprecise, it is quite likely that one side or other of the belt will escape entirely. This “over warning” is not like “crying wolf when there is no wolf. There is a hurricane, all right, even if happily it turns out to be somewhere else.

The actual diameter of the tropical cyclone determines the width of the belt that will be most seriously affected. With an allowance to either side for unpredicted deviations, a hurricane warning is issued for this belt. As the hurricane nears the coast this warning is regularly updated, with details of wind, rain, and storm surges as well as the speed and direction of its movement. The warnings must also distinguish the effects to either side of the center. Places near the eye wall and to the right of the track will experience the strongest winds and the heaviest rain will fall close to the eyewall.

If people act on the warnings, preparations for the storm will be completed by the time it arrives. Offshore installations, such as oil rigs, will have been evacuated. Fishing boats will be in harbors, tied up as securely as possible and their decks cleared of anything not fastened down. Larger ships will have moved into the most sheltered positions they can find. Factories in the path of the hurricane will have been closed and their machinery turned off. Offices will have been closed. All employees will have been advised to remain at home. Windows will have been boarded, on homes as well as shops and other business premises. People living on islands and along the coast will have been evacuated. Their numbers may have run into tens of thousands. If one or more cities are affected, the cost of these preparations runs into millions of dollars in materials, evacuation transport and accommodation, and lost production and if uncertainties in the strength or track of the hurricane mean the affected belt -has to be widened the costs increase still more. Because of the high cost, warnings try not to exaggerate the risk.

Hurricane's Damage

Unfortunately, warnings are not always heeded. People are understandably reluctant to make expensive preparations and may hope they are lucky or, by the time they start to appreciate the danger they are in, they may have left it too late. Often, these are people with no previous experience of conditions in the eyewall of a major hurricane (one of Saffir/Simpson category 3 or higher) and it is easy to dismiss the warnings when the sky is blue, the air calm, and the hurricane, if it exists at all, is far away over the sea. Mostly, they are recent arrivals, enjoying the apparently reliable sunshine, warmth, and beaches around their new homes. They will have seen TV news stories about hurricanes, but these cannot describe what it is like to be there, what the hurricane really looks, feels, and sounds like, and the ease with which it can pluck homes from the ground and smash them to firewood.

Such people are unwise. It is not only their own lives they risk, but those of the emergency personnel who may have to rescue them. When a hurricane warning is issued it means a hurricane is approaching. Warnings are not issued lightly and must always be taken seriously and acted on appropriately.

Filed Under: General How To's

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About the Author: Bruno Silva is an entrepreneur from Portugal with over 15 years of experience in Online Marketing. He is also a blogger and writes on variety of topics from online marketing to designs, cars to loans, etc.

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