MARINE WEATHER TERMINOLOGY

BEACH EROSION: The carrying and wearing away of beach materials, such as sand or rocks, by wave action, currents, tides, or wind.

CHART DATUM: The tidal datum to which soundings on a chart are referred, usually taken to correspond to low water elevation of the tide.

COASTAL FLOODING: The inundation of land areas along the coastal caused by sea waters over and above normal tidal action that may be originate from the ocean front, back bays, sounds, or other bodies of ocean water.

COASTAL FLOOD WARNING: Issued when tidal flooding or storm induced flooding is occurring, imminent, or highly likely along coastal areas within approximately the next twelve (12) hours.

COASTAL FLOOD WATCH: Issued when conditions are favorable for tidal flooding or storm induced flooding along coastal areas within approximately twelve (12) to thirty six (36) hours but the occurrence is still uncertain.

COASTAL WATERS: The marine area, including bays, harbors, and sounds extending from the coastal to twenty (20) nautical miles offshore.

CONTINENTAL SHELF: The zone bordering a continent and extending to a depth, usually around one hundred (100) fathoms to which there is a deep descent towards greater depth.

CONTINENTAL SLOPE: The area of descent from the edge of the continental shelf to greater depth.

DATUM: For marine interests, a base elevation used as a reference point from which a reckon heights or reckon depths.

DATUM PLANE: The horizontal plane, unique to each tidal station, to which soundings, ground elevations or water surface elevations for that station are referred.

FATHOM: Unit of depth in the ocean equal to six (6) feet.

FETCH: The marine area in which waves are generated by winds consisting of a near constituent direction and speed.

FREEZING SPRAY: An accumulation of freezing water droplets on a vessel caused by a combination of the wind, water, air temperature, and vessel movement.

GALE WARNING: Issued when sustained winds in the range of thirty five (35) knots to forty seven (47) knots are occurring or are imminent. Gale warnings are issued up to twenty four (24) hours before the above conditions are expected and are not associated with tropical systems.

GLOBAL MARINTINE DISTRESS AND SAFETY SYSTEM (GMDSS): An international agreed upon communication system for the distribution of safety information, including but not limited to weather warnings and forecasts to mariners.

GUSTS: A rapid fluctuation of wind speed with variations of ten (10) knots or more between peaks and lulls.

HEAVY SURF: Large waves breaking on or near the shore resulting from swells spawned from a distant storm.

HEAVY SURF ADVISORY: Issued for heavy or high surf, i.e. large waves breaking on shore because of swell from a distant storm. May pose a threat to life and property.

HIGH SEAS: The major oceans of the world including the coastal waters area and offshore waters area. Areas of responsibility for the United States are determined by international agreement.

KNOT: Unit of speed used for navigation interests. A knot is equal to one (1) nautical mile per hour or one point one five (1.15) statue miles (the length of one (1) minute latitude) per hour.

MARINE WEATHER STATEMENT: Issued to provide mariners with details on significant or potentially hazardous conditions not otherwise covered in existing marine warnings or statements.

MEAN HIGHER WATER WATER: A tidal datum which corresponds to the average mean of the higher tide water heights of a mixed tide observed over a specific nineteen (19) year period.

MEAN HIGH WATER: A tidal datum which corresponds to the average mean of high tide water heights observed over a specific nineteen (19) year period.

MEAN LOWER LOW WATER: A tidal datum which corresponds to the average mean of the lower low tide water heights of a mixed tide observed over a specific nineteen (19) year period.

MEAN LOW WATER: A tidal datum which corresponds to the average mean of low tide water heights observed over a specific nineteen (19) year period.

MEAN RANGE OF TIDE: The difference in height between mean high water and mean low water.

MEAN SEA LEVEL: A tide datum which corresponds to the average mean of hourly water elevations observed over a specific nineteen (19) years.

MEAN TIDE LEVEL: A tidal datum midway between mean high water and mean low water.

NAUTICAL MILE: Unit of distance used for marine navigation. A nautical mile is equal to approximately one point one five (1.15) statue miles (the length of one (1) minute latitude).

NAVIGATIONAL TELEX - (NAVTEX):A part of the Global Maritime Distress and Safety System (GMDSS) for automatically disseminating safety information, including but not limited to, weather warnings and forecasts to mariners. In text form via medium frequency radio to mariners within approximately two hundred (200) nautical miles of shore.

NEAP TIDE: Occurs the first and third quarters of the moon. Value is usually ten (10) to thirty (30) percent less than the mean tidal range.

OFFSHORE WATERS: The portion of the oceans, gulfs, and seas beyond the coastal waters (usually twenty (20) nautical miles) extending to a specific distance from a coastline (usually one hundred (100) nautical miles), a specific depth, or covering and area defined by a specific latitude and longitude points.

PERIOD: The interval between consecutive, similar stages in a cycle of events that repeats itself.

PREDOMINATE WIND: The wind that generates, or it's expected to generate, the significant sea conditions across the area.

RIP CURRENTS: Narrow channels of water flowing seaward from the beach through areas of breaking waves.

SAFETY NET: A satellite based part of the Global Maritime Distress and Safety System (GMDSS) for automatically disseminating safety information, including but not limited to weather warnings and forecasts to mariners, to mariners almost anywhere on the worlds oceans.

SEAS: Used to describe wind waves alone, combined seas or the wind wave component when swell is given in the forecast.

SEVERE LOCAL STORM WARNING: A severe thunderstorm warning or tornado warning that primarily refers to those warnings affecting adjoining coastal land and water areas.

SIGNIFICANT WAVE HEIGHT: The average wave height (trough to crest) of the one third (1/3) highest waves reported by an experienced observer.

SMALL CRAFT ADVISORY: Issued when sustained winds in the range of twenty five (25) to thirty four (34) knots and/or seas six (6) feet or higher are occurring or are imminent. Also issued to alert small boat operators of any sea condition that may be hazardous Small Craft Advisories are not associated with tropical systems. NOTE: There is no legal definition of the term "small craft".

SPECIAL MARINE WARNING: A severe local storm warning affecting coastal water area, or a warning for potentially hazardous weather conditions usually for two (2) hours of less and producing wind speeds of thirty four (34) knots or greater.

SPRING TIDE: Tides of increased range or tidal currents of increased speed that occur semimonthly as the result of the new moon or the full moon.

SQUALL: An increase in wind speed of sixteen (16) knots or more and sustained at twenty (20) knots or more for at least one (1) minute.

STORM SURGE: The difference between the astronomical tide and the observed tide.

STORM TIDE: The actual water level resulting from the astronomical tide plus the storm surge.

STORM WARNING: Issued when sustained winds of forty eight (48) knots or greater are occurring or are imminent. Storm Warnings are not associated with tropical systems.

SWELL: Wind generated waves that have traveled out of their area of origin. Swells characteristically exhibit smoother, more regular and uniform crests and a longer period than wind waves.

SURF: The waves in the area between the shoreline and the outermost limit of breakers.

TIDAL ANOMALY: Actual water level minus the tide table predictions.

TIDAL CYCLE: The periodic changes in the intensity of tides caused primarily by the varying relations between the Earth, Moon, an Sun.

TIDAL DATUM: A selected reference point that is used to define tide values.

TIDAL PILING: Abnormally high water levels caused by an accumulations of successive incoming tides that are not allowed to completely drain due to opposing strong winds and/or waves.

TIDE: The periodic rise and fall of water resulting from gravitational interactions between the Sun, the Moon, and the Earth. Also the vertical component of a tidal wave.

WATERSPOUT: A rapidly rotating column of air extending from a cumulonimbus cloud with a circulation that reaches the surface of the water, i.e. a tornado over water.

WAVE SPECTRUM: The distribution of wave energy with respect to wave frequency of period, helps to assist in differentiating between wind, waves, and swell.

WIND WAVES: Local, waves of short period generated from the action of wind only on the water surface.

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