Nor’easters usually do most of their damage along the coast, in the form of beach erosion and flooding. The northeast winds come from a low-pressure system offshore. These lows can originate anywhere from the Rocky Mountains to the Bahamas. Most of the strongest nor’easters originate in the Bahamas or over the Florida Peninsula.
The most destructive nor’easters occur when a high-pressure system over northeastern New England or in the northern Atlantic blocks the northward movement of the low. Winds blow clockwise around a high. Winds circulate counterclockwise around a low, so east winds or northeast winds batter the coast as the storm is southeast or east of the East Coast.
When the low stops moving, its winds combine with those of the high to blow in one direction over a long period of time, which creates huge waves. The duration of a nor’easter—the number of high tides through which it persists—can be the most significant measure of its destructiveness.
Hurricanes and Tropical Storms
Like all tropical cyclones, a hurricane needs the warm water of the tropics, which feeds the storm with energy.
In a mature hurricane, wind picks up warmth and moisture from the ocean, circling inward ever faster from outer cloud bands to the inner eyewall, where winds are the strongest and where it finally rises rapidly and is pushed out the top.
Most hurricanes that hit the United States begin either in the Caribbean or the Atlantic. Many of the worst start as seedlings coming off the coast of Africa.
In the beginning, a disturbance forms in the atmosphere, developing into an area of low atmospheric pressure. Winds begin to move into the center of the storm seedling from surrounding areas of higher air pressure. Warm water heats the air, and it rises as it nears the center.
The ocean feeds warmth and moisture into the storm, providing energy that causes the warm air in the center to rise faster. It condenses high in the atmosphere, creating thunderstorms. The tropical depression develops (if conditions are favorable) into a tropical storm, then finally into a hurricane, which is not unlike a giant swirling mass of thunderstorms.
As rising air in the storm's center condenses, it produces heat, forcing it to rise even faster. The air is pushed out the top -- much like smoke out the chimney of a fire -- and more air has to rush in at the surface to take its place. This kicks the ocean up more and, well, you can see that the storm essentially feeds on itself.
While many factors control the number of hurricanes in a given season, forecaster Bill Gray has said the long-term trend is ruled by a conveyor belt of sorts that moves Atlantic ocean water northward from near the Caribbean to an area east of Greenland.
There, the current sinks deep, moves southward and flows into the southern Atlantic Ocean and beyond. It's the warm, northward-moving surface water -- fuel for any hurricane -- that helps produce strongest storms.
Recent measurements (in 1999) show that the water in the conveyor belt contains more salt than normal. This increases the water's density, researchers explain, causing it to sink to greater depths. This in turn increases the flow of deep water southward, which forces an increase in the flow of warm, tropical surface water northward. Thus, the northern Atlantic becomes warmer than normal, providing the heat needed to turn hurricanes into powerful killers.
For a more detail look at hurricanes and tropical storms, see the National Weather Service's Tropical Prediction Center/National Hurricane Center web site.
The Division of Soil and Water Conservation's Shoreline Management Section monitors coastal areas during storms to assess beach erosion, dune damage and flood threats. In coordination with the Delaware Department of Transportation (DelDOT) and Delaware Emergency Management Agency (DEMA), these threats are evaluated to determine areas of probable road flooding and the site of dune breakthroughs. Every attempt is made to project where problem areas will be before damaging flooding or dune breakthroughs occur.
Post storm assessments are made to determine whether significant amounts of sand were lost from the beaches. The Shoreline Management Section provides technical assistance to local governments and property owners to help them recover from storms. Also, development along the Atlantic Ocean and Delaware Bay shorelines is regulated in order to reduce impacts on beaches and to reduce storm damage.