Impacts of Hurricanes

Hurricanes can have several types of impacts on humans and human activities. These impacts can range from enormous waves on the high seas to multiple tornadoes on land.

• Winds
• Storm Surge
• Rainfall
• Tornadoes
• Inland Impacts

The high winds of a tropical cyclone are a hazard for shipping and boating offshore. Near the eye of a hurricane, the wind is going in all directions in a very small area generating high waters that are moving in apparent random directions. This is much more hazardous than the waves formed by a winter storm that are all traveling in the same direction. The power of hurricane winds offshore was apparent in 1989, when Hurricane Gabrielle generated extremely high surf. Even though the eye of Gabrielle was several hundred kilometres away, beaches in Nova Scotia were closed due to the high surf while light winds and clear skies prevailed!

In coastal areas, the strong winds of hurricanes and tropical storms can cause significant damage. When a hurricane makes landfall or approaches a coast, winds, aside from producing storm surge, can destroy houses, buildings, and other structures. In major hurricanes, flying debris can be a hazard.

Storm surge is the rapid rise in sea level that occurs as a storm approaches a coastline. The sea level near the coast rises due to the high onshore winds that "pile up" the water near the coast. Also, when a hurricane passes, water is being pulled upward due to the extremely low pressure found near the centre of the storm. Storm surge is the highest on the front right side of Atlantic Hurricanes where onshore winds are the highest. Storm surge can also occur when a hurricane does not make landfall but moves along the coast. Low lying areas are the most vulnerable to storm surge and rapidly rising land will not be affected.

Storm surge in combination with high tides can have extremely devastating consequences. In 1900, 6,000 people were killed in Galveston, Texas mainly as a result of the storm surge that was associated with a Gulf of Mexico hurricane. In 1869, in New Brunswick and western Nova Scotia, a few days from the lunar perigee, a hurricane known as the Saxby Gale rose the tide up to 2 metres above normal. Many people lost their lives, hundreds of boats were beached due to the storm, and all low-lying areas were flooded.

When a hurricane makes landfall, rainfall can be excessive, particularly if the moist air of the storm is forced over mountain barriers. When a moist pocket of air is forced up into cooler air, the water droplets reach their dew point and rain is formed. Even relatively weak tropical storms can cause extreme rainfall. Heavy rains that exceed 100 millimetres over a 24 hour period can result in flooding. Many cities cannot handle such an increase in runoff because of the gentle topography in many of the coastal areas where hurricanes occur. Hurricane Beth of 1971 brought record rainfall amounts to Nova Scotia. Nearly 250 millimetres of rain fell in Halifax. Damage to crops, mainly due to flooding, was extensive and sections of highways and bridges were washed out. Total damage in Nova Scotia was estimated at $3.5 million.

Runoff can also be devastating in non-gentle landscapes. The steep topography can lead to flash floods and mud slides as occurred during Hurricane Mitch.

Small tornadoes may also develop in hurricanes. They usually develop in the front and right side (in the Northern Hemisphere) of hurricanes as they make landfall and begin to dissipate. The winds at the surface die off quickly and this creates a strong vertical wind shear that allows for the development of tornadoes. The damaging winds of hurricanes and tornadoes can sometimes cover the same path and it can be difficult to separate the damage. Hurricane Bertha of 1969, produced a swarm of over 100 tornadoes on the Texas coast. Tornadoes are generally not associated with tropical cyclones in Canada.

See The Canadian Connection

Although most of the impacts associated with tropical storms and hurricanes occur in the ocean and coastal areas, these storms can impact inland areas. The biggest threat to life and property inland is damage from flash flooding due to excessive rainfall. One of the most remembered Canadian hurricanes was Hurricane Hazel of 1954. Over 200 millimetres of rain fell in less than 24 hours triggering flash floods that killed 81 people in Southern Ontario.

Sometimes tropical cyclones produce relatively light rainfall right after landfall and a torrential downpour a few days later. This occurs when large quantities of tropical atmospheric moisture are released by a passing disturbance or by orographic features such as mountains. This occurred in central Virginia in 1969 when the moist air of Hurricane Camille was lifted by the mountains. In 6 hours almost 760 millimetres (30 inches) of rain fell, burying and drowning 109 individuals in flash floods.