What Are Nor'easters? Cyclonic Storms of the Atlantic

A nor’easter, or northeaster or Northeast storm, is a cyclonic storm system that forms in the mid-latitudes of the Northern Hemisphere and strikes the Atlantic coasts of the United States and Canada. Such systems generally involve gale-force winds and typically result in heavy rainfall and snowfall, sometimes as far inland as the Great Lakes. Although nor'easters may occur during any season, they are most common from September through April. Like other cyclonic systems in the Northern Hemisphere, nor'easters revolve counterclockwise and derive their names from the northeasterly winds that strike coastal areas ahead of the storms. Benjamin Franklin (1706-90) is credited with recognizing that nor’easters themselves move in a northeasterly direction.

Nor’easters develop in several ways. A low-pressure system from the eastern slopes of the Rocky Mountains or the Gulf of Mexico may move up the East Coast to form a more intense storm off Georgia or the Mid-Atlantic States before moving farther up the coast. On occasion, the warm water of the Gulf Stream generates a new storm off North Carolina or New Jersey that drains the energy from the original system. Such a storm will then increase in strength as it moves northeastward and picks up moisture from the water, reaching its greatest intensity off New England or the Maritime Provinces of Canada. A nor’easter may also form when a so-called Alberta or Canadian clipper storm system originating in southwestern Canada intensifies when it finally reaches the warmer water off New England.

Although nor’easters are much larger in extent than hurricanes, they usually lack the latter storms’ distinct “eyes.” Their winds are stronger aloft near the Earth’s surface but in general are weaker than those of hurricanes. However, the presence of a high-pressure system behind or ahead of the nor'easter will contribute to the strength of the storm’s winds, as will dropping pressure within the storm itself. In addition, a slowly moving nor'easter will drop more precipitation than a faster one. A classification scale similar to the Saffir-Simpson Hurricane Wind Scale has been developed for nor'easters by Robert E. Davis and Robert Dolan. Like the Saffir-Simpson scale, it employs a 1-to-5 (weak to extreme) measurement but is based primarily on the storm’s duration and wave height and is most useful for evaluating potential coastal damage and erosion. There are usually about twenty to forty nor’easters every year, of which at least two are likely to reach major intensity.

Aside from its cost in death and misery, an individual nor’easter can result in more than a billion dollars’ worth of damage, including serious beach erosion and flooding. The worst North American blizzards on record have been nor’easters, including a severe one in mid-March 1993, which affected much of eastern Canada and at least twenty-six states. This “Storm of the Century,” as it has been dubbed, resulted in snowfall from Alabama through Maine that has been estimated at nearly 13 cubic miles, spawned as many as fifty tornadoes, and led to a number of record low temperatures.

Even greater damage can occur when a nor’easter merges with another storm system. Sebastian Junger’s best-selling account The Perfect Storm and its 2000 film adaptation portray events occurring during the Halloween Nor'easter of late October 1991, when an already powerful nor'easter merged with Hurricane Grace before turning into yet another, albeit smaller, hurricane. The storm generated winds of 78 miles per hour and waves that may have reached 100 feet in height, and resulted in the death of a dozen people, including the entire crew of the fishing ship Andrea Gail. The storm caused damage as far away as Newfoundland in the north and Jamaica in the south, and was regarded as “perfect” because observers felt that it could not have been worse in meteorological terms.

FURTHER READING: Davis, Robert E. and Robert Dolan. 1993. “Nor’easters.” American Scientist 81: 428-39.

Junger, Sebastian. 1997. The Perfect Storm: A True Story of Men against the Sea. New York: Norton.

Kocin, Paul J. and Louis W Uccellini. 1990. Snowstorms along the Northeastern Coast of the United States: 1955 to 1985. Boston: American Meteorological Society.

Zielinski, Gregory A. 2002. “A Classification Scheme for Winter Storms in the Eastern and Central United States with an Emphasis on Nor’easters.” Bulletin of the American Meteorological Society 83 (1): 37-51.