History of Inland Flooding
Although cyclonic swells have been the first cause of death related to hurricanes in the past; during the last 30 years, even more people have perished as a result of inland flooding associated with tropical systems. Inland flooding has been responsible for half of the total deaths associated to tropical cyclones in the United States since the seventies. Flooding caused by hurricanes can take place thousands of miles away from the coastlines, placing at most risk communities that would usually be unaffected by the tremendous force of hurricane winds.
Some of the largest precipitations associated with tropical systems are produced by weak, slow speed Tropical Storms (from 1 to 10 mph) or Tropical Storms that have stationed over an area. Due to the amount of rainfall that a Tropical Storm is able produce, it may cause as much damage as a hurricane category 2.
Facts about Inland Flooding
Freshwater floods have been accountable for more than half (59%) of deaths caused by tropical hurricanes in the United States during the past 30 years. These floods are the reason why 63% of deaths associated to tropical hurricanes in the United States during that period occurred on inland counties.
• In the last 30 years, 78% of children that have perished due to tropical hurricanes have drowned in freshwater floods.
• A cubic yard of water weighs 1700 pounds. An average car weighs 3400 pounds. Many cars float in only two feet of water
• An average person can be dragged in six inches of moving water.
• The average car can be driven off the road in 12 inches of moving water.
• At least 23% of deaths associated to tropical hurricanes in the United States are people who drown inside their cars or while attempting to abandon them.
• Rainfall is typically more intense during slower advancing storms.
Dangers of a Hurricane: Storm Surges
Storm Surges
A storm surge is an abnormal increase in the sea level, sometimes it can be more than several meters in height and many miles in width. A storm surge will reach land up to five hours before the storm and destroy low-lying coastal areas. It is especially dangerous when the storm surge occurs during high tide and, in consequence, it is usually responsible of most hurricane related deaths.
A storm surge is a large water dome, often between 50 to 100 miles wide, that sweeps along the coastline close to the landfall point.
A storm surge range can be from 4 – 6 feet in height in small hurricanes, to more than 20 feet in the case of stronger hurricanes. The size of the storm surge is affected by the intensity of the hurricane and the depth of the coastline: a strong hurricane combined with a shallow coastline will result in a larger surge. The storm surge is the greatest threat to life and material assets along the coastline, even worse than strong winds.
• More than 6000 people perished during the Galveston Hurricane in 1900, most due to the storm surge.
• Hurricane Camille produced a 25 feet storm surge in Mississippi.
• In 1989, Hurricane Hugo generated a 20 feet storm surge in South Carolina.
Dangers of a Hurricane: Tornadoes
Hurricanes may produce tornadoes as well, worsening the destructive power of the hurricane. Usually, a tornado threat is related to the intensity of the hurricane: more intensity leads to greater threat. When a hurricane carries its winds inland, the quick moving air hits the terrain and structures, thus causing a friction convergence that enhances lifting.
Friction convergence is at least a contributing factor to tornado formation during a hurricane. The largest tornado concentration takes place in the right front quadrant of the hurricane.
There are several different theories about tornado origins, but in the case of Hurricane Andrew, small spinning vortexes inflicted serious damage; said vortexes were formed in areas with great wind cutting force in the wall of the eye of the hurricane.
The strong, harmful hurricane winds often cover the smallest tornado paths, making it very difficult to separate their damaging effects.
