Hurricanes and Coastal Storms

Hurricanes are among the most violent storms people suffer in the U.S. Gulf and Atlantic states. They are news before they happen, while they are happening, and sometimes for years after they happen.

Some hurricanes, like Hurricane Andrew, are mostly wind events. Others carry their punch with water. Hurricane Floyd was such a water event—unleashing torrents of muddy, polluted water upon thousands of people in North Carolina, Virginia, and New Jersey.

Born far out in the Atlantic, Floyd generated winds topping 135 knots as it advanced upon the southeast U.S. coast September 13, 1999. After menacing Florida, Georgia, and South Carolina, Floyd made landfall near Cape Fear, North Carolina, on September 16 with sustained winds near 110 mph. The maximum storm surge struck at high tide, contributing to extensive overwash, dune retreat, and damage to homes on barrier islands.

The water dumped by Floyd was devastating. Rainfall totaled a record 15 to 20 inches. Storm surges reached 10 feet in coastal North Carolina. This rain fell on lands still saturated from Hurricane Dennis less than two weeks earlier, and runoff was greater because water could not soak in. A month later, Hurricane Irene dumped another 5-10 inches of new rain on some of the areas hardest by Floyd.

Floyd killed 57 people—the deadliest U.S. hurricane since Agnes in 1972. Most of those killed drowned in North Carolina as rivers unable to handle the deluge swelled beyond known flood plains. Damage estimates topped $3 billion to $6 billion.

Even though hurricanes are a normal late-summer visitor to the Atlantic and Gulf coasts, Floyd taught savage lessons about expecting the unexpected. Beyond the lives lost and the homes and businesses destroyed, Floyd's flood waters killed 100,000 hogs in North Carolina, and washed out many of the huge lagoons where hog wastes were kept. Waters overflowed municipal wastewater systems, chemical storage areas, and farms. Nitrogen, phosphorus, bacteria, viruses, pesticides, heavy metals, ammonia, and fuel oil all poisoned the waters.

These hurricanes also left ugly scars on the east coast. While Hurricane Dennis was not a particularly strong storm, its week-long meandering off the coast, battering the shoreline with huge waves, produced some of the highest wave run-up ever recorded along the Outer Banks of North Carolina, changing the coastal geology of that area. Dunes, the first line of defense against the mighty power of the ocean, were washed away, destroying roads and making homes, businesses, and lives along the fragile, but popular coastline, especially vulnerable.

Hurricanes are worth covering because they hit people where they live. The triple whammy of Dennis-Floyd-Irene damaged roughly 40,000 homes—some 10,000 of them beyond repair.

Background and Context

"Hurricane" is the name given to the tropical cyclones with winds above 74 mph that hit the U.S. Gulf and Atlantic Coasts. Such storms draw their energy from the warm surface layer of tropical seas. As air warmed and moistened by the sea rises, it whirls into a vortex often hundreds of miles across. Perhaps only a third of the hurricanes that form will actually strike land.

Hurricane winds can be violently destructive. Winds are 131-155 mph for storms ranked category 4 on the Saffir-Simpson Scale—which are unusually intense. Winds go even higher for category 5 hurricanes, which are extremely rare. Hurricane winds can whip up waves of 50 feet or higher in the open sea. Convection creates an area of low pressure in the center of the vortex. This low-pressure area, along with high winds, creates a bulge-like rise in local sea level known as a storm surge. Storm surges are greatest on the right front side of the hurricane in the Northern hemisphere as water is pushed ahead of the storm. Severe storm surges can deliver a 20-foot or greater rise in sea level—and when this is combined with a high lunar tide and the pounding of enormous waves, the damage can be devastating.

A key to saving the human lives at risk in hurricanes is accurate, timely warning and evacuation. The Galveston hurricane of 1900 killed some 6,000 people largely because there was no warning system. The U.S. National Weather Service and related NOAA agencies have made enormous strides in measuring, understanding, and predicting hurricanes in recent decades—leading to much more effective warnings.

But even as improved warnings have been reducing deaths in the U.S., hurricane damage to property has been rising. This is not from any worsening of hurricane frequency or intensity but because of burgeoning population growth and building development in vulnerable coastal areas.

A recent study estimated that there are 338,000 buildings within 500 feet of the nation's coastlines. The FEMA study estimates that some 87,000 homes and other structures in that zone—more than a quarter of the total—are threatened by the erosion that severe coastal storms bring. About 60 million people live in coastal areas vulnerable to hurricanes, according to the Insurance Information Institute.

Despite some colossal disasters, climatologists say the past three decades have probably been a period of lower-than-normal hurricane activity (although it has been higher than normal in the last five years). Most current residents moved to coastal areas during this period of low hurricane activity, and NOAA estimates that 80 to 90 percent of them have never experienced a direct strike from a major hurricane. The result may be a false sense of security—not only affecting decisions on where to build and settle, but also affecting decisions on whether and when to evacuate.

The torrential rains that accompany hurricanes can often drop 6-12 inches of water in a very short time on areas far inland. In the last 30 years, inland flooding has been responsible for more than half the deaths associated with tropical cyclones in the United States.

Floods like the ones that came with Floyd illustrate the secondary hazards hurricanes can bring. In North Carolina, Virginia, Maryland, and New Jersey, floods brought additional threats of infection and ecological havoc. Storm surges and the incessant pounding by waves changed the coastline of North Carolina for years. In Honduras, the rains from Hurricane Mitch in 1998 unleashed a series of deadly landslides. Once they reach land, hurricanes may spawn tornadoes even as their maximum sustained winds are dying down.