Glossary

This page provides definitions of storm-related terms and acronyms.

Crest

When a river or creek floods, its crest is the highest level reached before the water goes back down.

Sand bags temporarily protect homes from beach erosion in Nags Head, NC.

http://www.daylife.com/photo/0e844u8g7Q6jC

Dune

A mound of sand that forms ridges along a coast. Sand dunes protect inland habitats from rising water and the force of waves. They can be natural or manmade.

Erosion

The process by which sediment, such as sand, is washed away by water or blown away by wind. This can cause beaches to gradually disappear into the ocean (see photo). Severe erosion usually occurs during storms.

Estuary

A semi-enclosed body of water where salt water from the ocean meets freshwater from rivers and streams.

In North Carolina, the Cashie, Chowan, and Roanoke Rivers converge to form the Albemarle Sound. The Neuse, Tar/Pamlico, and Pungo Rivers converge to form the Pamlico Sound. The area covered by the Albemarle, Croatan, Currituck, Pamlico, and Roanoke Sounds form the Albemarle-Pamlico Estuarine System.

This cross-section of a river compares normal water level with flood stage water level.

A hurricane's eye.

NOAA.

FEMA logo This cross-section of a river compares normal water level with flood stage water level.

How river flooding is measured.

Daniel Siepert, RENCI at ECU.

Extratropical

Extratropical storms are powered by the temperature difference between warm and cold air, but Hurricanes are powered by warm ocean water. Hurricanes can become extratropical as they move north, but their winds and rain can stay just as strong.

Eye

The cicle in the center of a hurricane where the winds are calm. The wall of clouds around the eye is usually where the winds are the strongest.

FEMA

Federal Emergency Management Agency. A government agency that coordinates the response to disasters that are too big for state and local governments to handle. The governor of a state must declare a "state of emergency" and officially ask for FEMA's help.

Flood Stage

The level at which a rising river or creek will begin to flood nearby buildings or streets. The amount of flooding is measured by how far the river has risen above its flood stage.

For example, the Tar River's flood stage in Greenville is 13 feet. If the water rises 15 feet, there will be 2 feet of flooding.

Hurricane

A seasonal tropical cyclone that occurs in the North Atlantic Ocean. Weaker storms are called tropical depressions and tropical storms. Hurricanes are measured on the Saffir-Simpson scale which measures wind speed and storm surge. A Category 1 hurricane is the weakest, while a Category 5 hurricane is the strongest.

This animation compares the different levels of destruction caused by different categories of hurricanes.

FoxNews.com

Category Wind (mph) Storm Surge (ft) Notes
Tropical Depression 0–38 0 Does not usually have a spiral shape or an eye.
Tropical Storm 39–73 0–3 Develops a spiral shape and receives a name.
Category 1 74–95 4–5 No damage to building structures; most damage to unanchored mobile homes, trees, and signs. Coastal road flooding and minor pier damage.
Category 2 96–110 6–8 Some damage to roofing materials, doors, and windows. Considerable damage to mobile homes, trees, signs, piers, and small boats. Some coastal evacuation routes flooded.
Category 3 111–130 9–12 Structural damage to some buildings; mobile homes are destroyed. Coastal structures are damaged by floating debris. Substantial regional flooding extends along rivers and sounds.
Category 4 131–155 13–18 Extensive structural damage with some complete roof failures. Major damage to lower floors of structures near the shore. All terrain lower than 10 feet above sea level may be flooded, requiring massive evacuation of residential areas as much as 6 miles inland.
Category 5 155+ 18+ Complete roof failures on many residences and industrial buildings. Some complete building failures. Major damage to all structures located less than 15 feet above sea level. Massive evacuation of all residents within 10 miles of the shoreline required.

Hurricane Warning

A warning that means hurricane conditions (strong wind and waves) are expected within 24 hours. A hurricane warning is more certain than a hurricane watch.

An inlet on Hatteras Island caused by Hurricane Isabel in 2003.

USGS.

NOAA logo

Hurricane Watch

An announcement that means hurricane conditions are possible within 36 hours. A watch is less certain than a warning.

Inlet

An explosed opening in a beach or island where water from the ocean meets water from an inland estuary (see photo). Inlets have strong currents and shifting sandbars beneath the water's surface. This makes them difficult for boats to navigate.

NOAA

National Oceanic and Atmosphereic Administration. A scientific agency charged with monitoring and protecting the Earth's oceans and atmosphere.

Nor'easter

A non-tropical coastal storm generally forming between October and May. Unlike hurricanes, nor'easters have a cold core and are much larger in size. The winds of a nor'easter are not centered around an eye and are not as strong as those of a hurricane.

The Nor'easter of 1993 brought 11.3 feet of storm surge and eleven tornadoes to Flordia, as well as 50 inches of snow to Mt. Mitchell, NC. The "Ash Wednesday Storm" of 1962 was also a nor'easter.

NWS logo

NWS

National Weather Service. A branch of NOAA which provides weather forecasts and warnings. NWS has three offices in North Carolina: Newport, Raleigh, and Wilmington.

Sandbar

A long and narrow body of sand, usually parallel to beaches (see photo). Sandbars also cause waves to break before reaching the shoreline. This helps protect beaches from erosion. Sandbars are also known as shoals.

How storm surge combines with the tide to flood coastal areas.

Modified from the National Hurricane Center.

USGS logo

Storm Surge

Water that is pushed ashore by a storm's winds. This advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the average water level 15 feet or more.

This rise in water level can cause severe flooding in coastal areas, particularly when the storm tide coincides with the normal high tides. Because much of the United States' densely populated Atlantic and Gulf Coast coastlines lie less than 10 feet above mean sea level, the danger from storm tides is tremendous.

USGS

United States Geological Survey. A scientific government agency that studies the United States' landscape, natural resources, and natural hazards.


Sources: National Hurricane Center Glossary; NC COHAZ Glossary; NOAA; NWS;
North Carolina's Hurricane History by Jay Barnes; Wikipedia: The Free Encyclopedia.