The glossary of surf forecasting terms
- 24 March 2017 | Surfing
What is the definition of swell? What are the parts of a wave? What the most important surf forecasting terms? How do you name the highest part of a wave?
Surf science has its own expressions. That is why we've decided to "translate" some of the most relevant wave terms. Surf forecasting is the art of predicting how the ocean waves will arrive and break at our shores. It's more efficient than a crystal ball because it truly works.
Surf scientists have been fine-tuning the variables involved in oceanography and meteorology using technological tools, computational models, and advanced mathematical calculations to anticipate our surf session.
Data gathered from ocean buoys might not be enough, though. Surf forecasters need to add bathymetric information and near-shore obstacles to their analysis before delivering accurate reports.
However, every surfer should know the basics of surf forecasting. There's no of understanding how our local break work than to learn the fundamentals of swell formation.
Let's take a look at the scientific names that usually appear in the surf forecast terminology.
Angular Spreading - the lateral spreading of the waves as they propagate from the fetch;
Backwash - the movement of a wave that returns to the ocean after washing up the beach. Also known as clapotis;
Bathymetry - the topographic study of the sea bottom;
Beaufort Scale - a wind speed scale based on visual observations of the sea or land;
Berm - a steep bank of sand formed in the shoreline;
Breaker - a wave that is breaking after reaching maximum steepness;
Capillary Wave - the first waves produced by the win in a flat sea;
Centrifugal Force - an imaginary inertial force directed away from the axis of a rotating body;
Chop - small waves featuring short crests that appear following wind interaction;
Cold Front - an imaginary line that separates cold and warm air in a low-pressure system;
Corduroy - swell lines that appear on the horizon;
Coriolis Effect - the tendency for large masses of water to move toward the right in the northern hemisphere and to the left in the Southern Hemisphere, relative to an observer looking toward the equator;
Crest - the highest part of a wave;
Cyclone - a system of winds that rotates around a strong center of low atmospheric pressure taking place in the South Pacific and the Indian Ocean;
Deep Water Wave - a wave with a depth/wavelength ratio greater than one-half;
Diffraction - the behavior of a wave when encounters a barrier or obstacle.
Dispersion - the tendency of longer waves to travel faster than shorter waves due to the proportionality between wave phase speed and wavelength;
Diurnal Tide - an area with one high tide and one low tide per day;
Drag Force - a force acting in a direction opposite to the motion of any object moving in a moving fluid;
Eddy - a swirling movement of air or water;
Fetch - the length of an area over which the wind blows continuously to generate waves;
Fully Developed Sea - the moment the waves reach maximum height before breaking. Also known as Fully Arisen Sea;
Gravity Wave - a wave that has gravity as its restoring force;
Groundswell - a group of waves generated by an offshore weather system which propagates away from the storm center, and travels thousands of miles before reaching the shore;
High Pressure - a region where the atmospheric pressure at the surface is greater than its surrounding area. Also known as anticyclone;
Hurricane - a system of winds that rotates around a strong center of low atmospheric pressure taking place in the Atlantic and Northeast Pacific;
Inertial Force - the force acting on a body that results from the acceleration of water particles away from an accelerating body;
Isobar - a line on a weather map connecting areas having the same atmospheric pressure;
Jet Stream - a vigorous and fast westerly air current found in the mid-latitudes that influence the formation of low-pressure systems;
Knot - a unit of speed equivalent to one nautical mile (1.151 mph, 1.852 km);
Low Pressure - a region where the atmospheric pressure at the surface is lower than its surrounding area. Also known as mid-latitude depression;
Mean Wave Direction - the primary swell direction, or the average of all the individual wave directions in a given period of time;
Neap Tide - a tide after the first or third quarters of the moon when there is the least difference between low and high water. It occurs seven days after a spring tide;
Refraction - the bending of a traveling wave as it interacts and propagates over different ocean depths. It has a high impact on wave height;
Rip Current - a powerful and sometimes unpredictable surface current of short duration flowing seaward from the shore;
Roaring Forties - strong westerly winds that blow around the planet in the southern hemisphere, usually between the latitudes of 40 and 50 degrees;
Rogue Wave - a spontaneous extreme deep water wave that exceeds the significant wave height by more than a factor of two;
Rule of Twelfths - a method used by sailors to estimate the height of the tide at any moment, given only the time and height of low and high water;
Semi-Diurnal Tide - an area with two high and two low tides per day;
Set - a series of waves that is larger than the average for a given day. Also known as wave group;
Shallow Water Wave - a wave with a depth/length ratio of less than 1/20;
Shoaling - the effect and changes in wave height as waves enter shallow waters. It has impacts on wave height, and in the direction of the breaking wave.
Significant Wave Height - the average wave height of the highest one-third of all waves in a time series;
Significant Wave Period - the average wave period of the one-third highest waves;
Spring Tide - a tide just after a new or full moon, when there is the greatest difference between low and high water;
Storm Surge - a sudden and abnormal increase in sea level near the coastline due to onshore winds or groundswells;
Swell - a group of long-period waves generated by distant weather systems that travel thousands of miles before hitting the shores;
Tidal Bore - a wave moving upstream in a river caused by the interaction of the tide with the river flow;
Tidal Range - the vertical difference between the low tide and the succeeding high tide;
Tide - the rise and fall of sea level caused by the interaction of the gravitational force exerted by the moon and the sun and the rotation of the Earth;
Trough - the lowest part of a wave between successive crests;
Typhoon - a system of winds that rotates around a strong center of low atmospheric pressure taking place in Northwest Pacific;
Warm Front - transition zone, generally moving from southwest to northeast, where a warm air mass is replacing a cold air mass;
Wave Decay - the change which occurs in waves when they leave a fetch and travel through a region of lighter winds;
Wave Group - a series of waves propagating together in which the wave direction, wavelength, and wave height vary only slightly. Also known as set waves;
Wave Period - the time between two successive wave crests;
Wave Spectrum - a method of representing the distribution of wave energy on the sea surface;
Wave Steepness - the height of a wave divided by its wavelength;
Wave Train - a series of waves traveling in the same direction. Also known as swell;
Wavelength - the horizontal distance between the crest of one wave to the crest of the next wave;
Whitecaps - small windblown waves that break and disappear;
Windswell - short-period waves created by local winds near the shore;
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