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Hurricanes And Their Damage

Each year an average of ten tropical storms develop over the Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico. Many of these remain over the ocean, with approximately six of these storms becoming hurricanes each year. In an average 3-year period, roughly five hurricanes strike the United States coastline, anywhere from Texas to Maine, also affecting the lower eastern coastline of Canada.

Whether you live on the coast, have a condo in the Florida panhandle or are vacationing in the warm tropics of the Caribbean, hurricanes pose an enormous threat to humans and their habitat. The magnitude of these storms can devastate towns, ripping buildings apart and causing disastrous flooding hundreds of miles inland.

What Is A Hurricane?

Tropical cyclones, which are simply low-pressure systems that have developed over tropical or sub-tropical waters, are the starting point for a hurricane. When winds of a tropical storm (39-73 mph) reach a constant speed of 74 mph or greater the storm can then be classified as a hurricane.

Typically, the season for the Atlantic Basin (Atlantic Ocean, Caribbean Sea and the Gulf of Mexico) runs from June 1 to November 30, with hurricanes ranging up to 400 miles in diameter. The term hurricane is adapted to any such storm occurring in the North Atlantic, but be aware that in other parts of the world they are referred to as typhoons and severe tropical cyclones.

The main parts of a hurricane are:

The Eyewall

The eyewall surrounds the eye and is composed of intense thunderstorms, which have the strongest winds in the entire system. Changes in the structure of the eye and eyewall can cause changes in the wind speed, which is an indicator of the storm’s intensity. The eye can grow or shrink in size and double (concentric) eyewalls can form.

The Rainbands On Its Outer Edges

The storm’s outer rainbands are made up of dense bands of thunderstorms which spiral slowly counterclockwise (in the northern hemisphere), ranging in width from a few miles to tens of miles. They can be 50-300 miles long and can extend hundreds of miles from the centre, usually having hurricane or tropical storm-force winds. Sometimes the bands and the eye are obscured by higher-level clouds making it difficult for forecasters to use satellite imagery to monitor the storm.

Understanding Hurricanes And Their Hazards

Hurricanes gain their strength from low surface pressure, evaporation off warm seas; any condensation in the air and clouds that may already be present in the area.hurricane

As a general rule of thumb, the hurricane’s right side (relative to the direction it is traveling) is the most dangerous part of the storm because of the additive effect of the hurricane wind speed and the speed of the larger atmospheric flow (steering winds). The increased winds on the right side increase the storm surge; wreaking havoc on cities located to the top right of a hurricane when it makes landfall.

The extensive damage done to inland homes is due to these terribly strong winds that can tear the roofs off houses, uproot trees and throw debris around with ease. Rocks, tree limbs, and solid objects are picked up, become flying missiles and are hurled into buildings by the wind. Being forceful enough to break windows and doors, these projectiles allow unforgiving winds inside a home. In extremely strong hurricanes, such as Hurricane Andrew, the winds can be strong enough to collapse any weak parts of a house.

Even though hurricane winds are deadly enough on their own, hurricanes also bring with them storm surges, floods and tornadoes that have their own devastating effects. The danger with tornadoes spawned by hurricanes is the lack of warning signs that people associate with them. Usually hail or a lot of lightning accompanies tornadoes, but in this case they come as a surprise. It is therefore best if you remain indoors, in the centre of your house and away from windows.

The risk of flooding depends on a number of factors: the speed of the storm, its interactions with other weather systems, the terrain it encounters, and ground saturation. Flooding is not only caused by storm surges, but also by torrential rains that hurricanes bring, which can reach hundreds of miles inland. A typical hurricane brings at least 6-12 inches of rainfall to the area it crosses. The resulting floods can cause considerable damage and loss of life, especially in mountainous areas where heavy rains produce flash floods and as a consequence result in devastating mudslides.

Although all these factors are dangerous, the most deadly force of all is the storm surge. A storm surge is a large dome of water, 50-100 miles wide, which sweeps across the coastline near where a hurricane makes landfall. Driven by high winds, any hurricane that makes a perpendicular landfall or hits at high tide creates tremendous damage. Nine out of ten hurricane fatalities can be attributed to storm surge or flooding.
The life of a hurricane can last more than two weeks over open waters and can run a path across the entire length of the eastern seaboard.
How Does A Hurricane Form?
Although tropical storms can rapidly intensify, very few of them ever become hurricanes at all. There are certain factors and stages that a storm must go through in order to develop into a threatening tropical cyclone.

The components needed for a hurricane include a pre-existing weather disturbance, warm tropical oceans (at least 80 degrees Fahrenheit to a depth of about 150 feet), moisture, and relatively light winds. If the right conditions persist long enough, they can combine to produce the violent conditions of a hurricane.

In these early stages, the system appears as a relatively unorganized cluster of thunderstorms usually forming in the Caribbean or off the west coast of Africa. They slowly drift westward fueled by the warm waters of the tropics and if the conditions are right, the system can develop into a tropical depression. Heat and energy for the storm are gathered through contact with warm ocean waters.

The winds near the ocean surface spiral into the disturbance’s low-pressure area and warm, moist air moves toward the centre of the storm. At this point, the storm begins to take on the familiar spiral appearance due to the flow of the winds and the rotation of the earth. The warm air then condenses into drops as it spirals upward, producing torrential rains and releasing more heat. This additional heat further powers the storm and brings the tropical depression to tropical storm status.

As the updrafts suck up more water vapour, it triggers a cycle of strengthening that can be stopped only when it has made contact with land or cooler water. Bands of thunderstorms form and the storm’s cloud tops rise higher into the atmosphere. If the wind forces at these high elevations remain relatively small (no wind shear), the storm can remain intact and continue to strengthen. When the winds reach a minimum of 74mph (64 kt) it is classified as a hurricane and its characteristic eye forms
Hurricane Naming System

Although the US National Weather Service started using lists of names to identify hurricanes in 1953, giving names to hurricanes actually began hundreds of years ago.

They used to be named after the particular Saint’s Day on which they occurred. It wasn’t until the late 19th century that an Australian meteorologist started giving female names to the tropical storms.

Then in 1979, male names were added to the list and all names were used except for those starting with Q, U, X, Y and Z (in the Atlantic). There are other regions besides the Atlantic that have different lists with different rules (different letters omitted), depending upon the languages spoken in that region e.g. Eastern Australian Region names, Fiji Region names, Central North Pacific names.

The continued adoption of names can be explained from past experience; the use of short, distinctive names (e.g. Erin, Sam, Victor) is quicker and less subject to error than older methods of latitude-longitude identification.

Hurricane names are chosen from a list selected by the World Meteorological Organization, which uses six lists in rotation and these same lists are reused every six years. The lists appear in alphabetical order and alternate between female and male names. The only time a new name is added is when a hurricane has been so deadly or costly that its name is retired.

The first name ever to be retired was that of Carol who caused 60 deaths and property damage estimated at $1.93 billion (in 2003 dollars). With more than half the damage occurring in North Carolina, it was the most expensive hurricane in US history at that time. Some other examples of those names that have been retired are: Andrew, Carla, Donna, Hazel, and Mitch.

Damage caused by Hurricane Carol
Airplane view looking up at eyewall
Interesting Fact #2

Why do hurricanes hit the East Coast and not the West Coast?

The larger atmospheric flow in which tropical and subtropical cyclones form generally travels in a west-northwest direction (in the northern hemisphere). 

That flow can easily bring hurricanes toward the East Coast, but it generally carries them away from the West Coast. Also, the waters of the Gulf Stream along the East Coast are quite warm (over 80°F) in comparison to those along the West Coast, which rarely get above 75°F. Remember that hurricanes need warm water to both develop and maintain their intensity

Storm surge
Hurricane Watch Centres

Over the past 20 years, improvements in hurricane computer modeling, observational instrumentation and better training for forecasters have greatly increased forecast accuracy.

Despite these advances, the many complex interactions that occur within the atmosphere are not fully understood or adequately modeled, producing errors in forecasts.

The National Weather Service along with other agencies has several tools to monitor hurricanes. While they are still far out in the ocean, indirect measurements of tropical storm and hurricane dimensions as well as their wind speeds using satellites are the main tool, although ships and buoys also provide observations.

Once the storms come closer to land, more direct measurements such as reconnaissance aircraft, radiosondes (upper air measurements), and automated surface observing stations (surface conditions) are also used. Once the system is within about 200 miles of the coast, radar provides important indirect measurements of the storm.

Organizations, like the National Hurricane Centre near Miami, constantly watch the North Atlantic, Caribbean, and the Gulf of Mexico waters for tropical disturbances.

Once these disturbances reach a certain wind speed and are moving in a circular pattern they are immediately reported as tropical storms, which can then grow into hurricanes.

Whether small or big, these tropical systems are tracked while they are still far out to sea. Most weather channels run active weather segments, including tropical updates every hour to keep viewers up to date.

Continuous coverage is provided during an approaching landfall and if you are located in that area, you need to make arrangements incase of an emergency.

On The Horizon
Up until now, NASA has been using satellite imagery that could only determine how big the system was, give us pictures of the clouds and the top of the storm, but we were really only scratching the surface. Thanks to recent technology, predicting a hurricane's intensity may be getting a little easier. Using a satellite equipped with radar, meteorologists have been producing stunning pictures of the internal structures within a hurricane. This imagery has revealed extremely violent thunderstorms called hot towers. Currently there is not enough evidence to prove anything but specialists say they may be giving us a clue that storm is releasing a lot of energy. There is a possibility that there is a link between the intensity and hot towers. If this turns out to be true, meteorologists will be able to predict whether a hurricane will weaken or intensify just before landfall. Emergency officials will be able to evacuate cities when needed and prevent innocent people from being trapped in an unexpected category 4 or 5 hurricane.
A Bright Future

The National Oceanic and Atmospheric Administration (NOAA)

has recently introduced a new way to follow specific tropical storms or hurricanes. The NOAA Storm Tracker contains live links to advisories, tracking maps and satellite images of a particular storm that is project to strike nations in a storm’s path. The live links will update automatically without having to refresh or reload the browser window.

Storm Terms

Tropical Cyclone – generic term for any organized low-pressure system, which develops over tropical and sometimes subtropical waters. Temperatures in the centre of the system are warmer than those on its periphery. Tropical depressions, tropical storms and hurricanes are all examples of tropical cyclones.

Tropical Wave – a low-pressure trough moving generally westward in the trade winds.

Tropical Disturbance – an organized area of showers and thunderstorms. Typically they maintain their identity for at least 24 hours and are accompanied by heavy rains and gusty winds.

Tropical Depression - an organized system of clouds and thunderstorms with a defined circulation with maximum sustained winds 38 mph or less (33 kt).

Tropical Storm – similar to a tropical disturbance, it is a tropical cyclone with strong thunderstorms and defined circulation with maximum sustained wind   speeds that range from 39-73 mph (34-63 kt).

Hurricane – a warm core tropical cyclone with maximum sustained winds of at least 74 mph (64 kt).

Eye Wall – location within a hurricane where the most damaging winds and intense rainfall are found.

The Demise Of A Hurricane

Similar to the birth of a hurricane, there are many elements contributing to its decay. Wind shear alone can tear the hurricane apart, but other factors such as moving over cooler water or drier areas can lead to the weakening as well.

Another cause of its dispersion is landfall. Once a hurricane moves inland its main moisture source is cut off, and its movement can be reduced by friction with terrain. If, however, the weakening hurricane moves into a more favourable region or interacts with mid-latitude frontal systems, the hurricane or tropical cyclone can re-intensify.

Interesting Fact #1

The sun's radiation reaches its peak in June in the tropical Northern Hemisphere. Why, then, doesn’t the hurricane season peak in June?

Although solar radiation peaks in June, it takes a while for the oceans to absorb that heat and reach their warmest temperatures.  The sun warms the ocean surface first, and these temperatures mix with the cooler water below. The ocean takes time to warm to a great enough depth to support tropical cyclone development.  Remember also that hurricane formation requires a number of elements, not just warm ocean waters and that combination usually comes together in summer and early fall.

Damage Done

It is impossible to overstate the amount of damage these storms can bring when you take into consideration the lives lost and the millions to billions of dollars in property damage.

To name a few:

In 1900, a hurricane demolished Galveston, Texas, racking up to over $809 million dollars in damage and over 8000 lives lost.

In 1938, taking 600 lives, a huge hurricane pounded New England causing $4.1 billion dollars in damage.

Hurricane Andrew gave no mercy when in 1992 it claimed 26 lives and added up to a whopping $26.5 billion in damage.

In 1969, it wasn’t the 24.6-foot storm surge that Hurricane Camille brought that was responsible for the majority of deaths; it was the rains that reached as far inland as West Virginia.

The intensity of the hurricane is an indicator of damage potential, however, impacts are a function of where and when the storm strikes.

In 1955, Hurricane Diane hit the northeastern US and caused 184 deaths. It was only a category 1 hurricane but the 13th deadliest since 1900.

The year 1972 brought Hurricane Agnus, also a category 1 hurricane, ranking 5th deadliest with damages estimated at $6.9 billion.

Our Biggest Problem

Through research and technology we have been able to determine the time of year hurricanes take place, how they are formed and how to evacuate towns and cities when the threat to the coastlines becomes too great. The one piece to the puzzle that we are missing is what causes hurricanes to move the way they do, switch directions and why they suddenly intensify.

A hurricane’s speed and path depend on complex interactions between the storm, with its own internal circulations, and the earth’s atmosphere.

The air in which the hurricane is embedded is constantly moving and changing, containing high and low pressure systems that can greatly alter the speed and path of the hurricane. In turn, it can modify the environment around the storm. Some hurricanes follow a fairly straight course, while others loop and zigzag along the path. These seemingly erratic changes are difficult to forecast.

Computer models used to forecast storm intensity and movement requires a great deal of data about the atmosphere. Lack of observations (especially over the ocean) and errors and inconsistencies in the data are major sources of forecast errors.

Researchers have been working on longer-range predictions of hurricane activity. They have not yet found any relation between storm activity early in the hurricane season and activity in the rest of the period.

We do know that over many years hurricanes have cycles of greater and lesser activity. Current research is showing promise for forecasting annual tropical storm and hurricane activity a year or more in advance but there are no techniques that can make long-range predictions of the specific locations where hurricanes will strike.